This document provides three recipes for producing salt. Recipe #1 describes the geological process of plate tectonics, wherein salt deposits form deep underground over millions of years within shifting continental plates. Recipe #2 involves a chemical reaction but is not described. Recipe #3 depends on water evaporation from seas and salt pans. The document discusses the historical and economic importance of salt and how its production and trade influenced civilizations and politics over centuries.

1. LECTURE 17 An IONIC COMPOUND that CHANGED the
WORLD
Salt (NaCl) comes from dead, dried-up seas or living ones. It
can bubble to the surface as brine or outcroppings in the form of
salt licks and shallow caverns. Below the surface of the earth, it
is deposited in white veins, some of them thousands of feet
deep. It can be evaporated from salt “pans,” boiled down from
brine, or mined from shafts extending half a mile down. Since
Neolithic times, salt from upwelling brine was recovered in an
area on the outskirts of present-day Kraków, Poland, and
excavations began in the 13th century. The crown jewel of the
Wieliczka salt mine is St. Kinga's Chapel (above), which is
sculpted entirely in salt. The mine reaches a depth of almost
1100 feet, and extends via horizontal passages and chambers for
over 178 miles. Over the centuries, among the visitors of the
Wieliczka salt mine were Copernicus, Goethe, Chopin
and Mendeleev.
The “history of the world according to salt” is simple: animals
wore paths to salt licks; men followed; trails became roads, and
settlements grew beside them. When the human menu shifted
from salt-rich game to cereals (see Lecture 1), more salt was
needed to supplement the diet. Since underground deposits were
beyond reach, and the salt sprinkled over the surface was
insufficient, scarcity kept the mineral (Halite) precious. As
civilization spread, salt became one of the world’s principal
trading commodities.
Salt routes crisscrossed the globe. One of the most traveled led
from Morocco south across the Sahara to Timbuktu. Ships
bearing salt from Egypt to Greece traversed the Mediterranean
and the Aegean.

2. Herodotus (484-425 BC), “The Father of History,” a title first
conferred on him by Cicero in the first-century BC, describes a
caravan route that united the salt oases of the Libyan desert.
The passage is in his book The Histories, a detailed record of
his inquiry on the origins of the Greco-Persian Wars.
Venice’s glittering wealth was attributable not so much to
exotic spices as to commonplace salt, which Venetians
exchanged in Constantinople for the spices of Asia. In 1295,
when he first returned from Cathay, Marco Polo delighted the
Doge with tales of the prodigious value of salt coins bearing the
seal of the great Khan.
As early as the 6th century, in the sub-Sahara, Moorish
merchants routinely traded salt for gold, ounce for ounce. In
Abyssinia (Ethiopia), slabs of rock salt, called ‘amôlés, became
coin of the realm. Each one was about ten inches long and two
inches thick. Cakes of salt were also used as money in other
areas of central Africa.
Not only did salt serve to flavor and preserve food, it made a
good antiseptic, which is why the Roman word for these
salubrious crystals (sal) is a first cousin to Salus, the goddess of
health. Of all the roads that led to Rome, one of the busiest was
the Via Salaria, the salt route (in gray on the map below), over
which Roman soldiers marched and merchants drove oxcarts full
of the precious crystals up the Tiber from the salt pans at Ostia.
A soldier’s pay, consisting in part of salt, came to be known as
solarium argentum
(“salt money”), from which we derive the word salary. A
soldier’s salary was cut if he “was notworth his salt,” a phrase
that came into being because the Greeks and Romans often
bought slaves with salt.

3. “With all thine offerings thou shalt offer salt,” says Leviticus
2:13. Because of its use
as a preservative, salt became a token of permanence to the
Jews of the Old
Testament. Its use in Hebrew sacrifices as a meat purifier came
to signify the eternal
covenant between God and Israel. In Genesis 19:1-29, two
angels of the Lord
command Lot, his wife and two daughters to flee the sinful city
of Sodom without
ever looking back. When Lot’s wife cast a fleeting glance
backward, she was
transformed into a pillar of salt.
A Roman religious ritual in which grains of salt were placed on
an eight-
day-old babe’s lips, is a precedent for the Roman Catholic
baptismal ceremony in
which a morsel of salt is placed in the mouth of the child to
ensure its allegorical
purification. In the Christian catechism, salt is still a metaphor
for the grace and
wisdom of Christ. When Matthew says, “Ye are the salt of the
earth” he is

4. addressing the worthy sheep in the flock, not the erring goats.
During the Middle Ages, the ancient sanctity of salt slid toward
superstition. The spilling of salt was considered ominous, a
portent of doom. (In Leonardo da Vinci’s painting The Last
Supper, the scowling Judas is shown with an overturned
saltcellar in front of him.) After spilling salt, the spiller had to
cast a pinch of it over his left shoulder because the left side was
thought to be sinister, a place where evil spirits tended to
congregate.
The social symbolism of salt continued as late as the 18th
century. The rank of guests at a banquet was gauged by where
they sat in relation to a silver saltcellar on the table. The host
and “distinguished” guests sat at the head of the table, “above
the salt.” People who sat below the salt, farthest from the host,
were regarded of little consequence.
Salt taxes either solidified or helped dissolve the power of
governments. For centuries the French people were forced to
buy all their salt from royal depots. The gabelle, or salt tax,
was so high during the reign of Louis XVI that it became a
major grievance and eventually helped ignite the French
Revolution. Lavoisier was a powerful member of a number
of aristocratic councils, and an administrator of the Ferme
générale, one of the most hated organizations of the Ancien
Régime because of the profits it took at the expense of the state,
the secrecy of the terms of its contracts, and the violence of its
armed agents. All of these political and economic activities
enabled Lavoisier to fund his scientific research. At the height
of the French Revolution, he was charged with tax fraud and
selling adulterated tobacco, and was guillotined on the Place de
la Concord, the largest square in Paris. Today, the American
Embassy is on this square. In the Ambassador’s office, there is
a remarkable portrait of Benjamin Franklin (who was in
Lavoisier’s inner circle of friends), which (in my view) captures
the essence of Franklin far more than the one by Duplessis in
the National Portrait Gallery.

5. As late as 1930, in protest against the high British tax on salt in
India, Mahatma Gandhi led a mass pilgrimage of his followers
to the seaside to make their own salt.
If the importance of a food to a society can be measured by the
allusions to it in language and literature, then the significance
of salt is virtually unrivaled. Nearly four pages of the Oxford
English Dictionary are taken up by references to salt, more than
any other food. For example, taking something with a “grain of
salt” is a recipe for skepticism.
In this Lecture, I will give three “recipes” for producing salt.
The first is geological, the second is via chemical reaction, and
the third depends on another “Molecule that Shaped the World,”
water.
RECIPE #1. TECHTONIC APPROACH
Alfred Wegener (1880-1930) was a German meteorologist and
geophysicist. During his lifetime he was known primarily for
his pioneering polar research in Greenland, and for his
achievements in meteorology. Today he is most remembered as
the originator of the theory of Continental Drift. In 1912 he
hypothesized that the continents are slowly drifting around the
Earth (German: Kontinentalverschiebung).
Wegener first thought of this idea by noticing that the different
large landmasses of the Earth almost fit together like a jigsaw
puzzle. The continental shelf of the Americas fits closely to
Africa and Europe. Antarctica, Australia, India and Madagascar
fit next to the tip of Southern Africa.
Wegener drew together evidence from various fields to advance
his theory that there had once been a giant continent, which he
named "Urkontinent" (German for "primal continent",
analogous to the Greek "Pangaea", meaning "All-Lands" or

6. "All-Earth").
In particular, he analyzed both sides of the Atlantic Ocean for
rock type, geologicalstructures and fossils. He noticed that
there was a significant similarity between matching sides of the
continents, especially in fossil plants.
Shown below are the world maps created by Wegener showing
Pangaea and the continents drifting apart. Its spatial and
temporal classification corresponds to his conception at that
time, not to the later proven positions and geological epochs.
Wegener put forward his hypothesis in 1912, the same year that
Rutherford was carrying out his “gold foil” experiments and
developing his “Solar System” model of the atom. Both models
when first reported were controversial and, in fact, Continental
Drift was widely rejected by mainstream geology until the
1950s, when numerous discoveries such as paleomagnetism
provided strong support for Continental Drift, thereby
establishing a basis for today's model of Plate Tectonics.
PlateTectonics (from the ancient
Greek: τεκτονικός, “pertaining to building”) is a scientific
theory describing the large-scale motions, beginning 3.3 - 3.5
billion years ago, of seven or eight large plates (and the
movements of a larger number of smaller plates) in
the outermost shell of the Earth. The outermost shell is called
the lithosphere.The above diagram shows the internal layering
of the Earth, lithosphere above the asthenosphere. The
asthenosphere is the highly viscous, mechanically weak and
ductile region of the upper mantle of the Earth. It lies below the
lithosphere, at depths between approximately 50-125 miles
below the surface of the Earth. The outer core is about 1,400
miles thick, and it's made of an alloy (see Lecture 2)
of iron (Fe) and nickel (Ni), along with small amounts of other

7. dense elements like gold (Au), platinum (Pt), and uranium (U).
Natural background radiation (see Lecture 16) in our everyday
lives comes mainly from the radioisotopes of uranium, thorium
and potassium and their decay products some of which, like
radium and radon are intensely radioactive but occur in low
concentrations. Most of these sources have been decreasing,
via radioactive decaysince the formation of the Earth (there is
no significant amount currently being transported to the Earth
from “outer space”). The present radioactivity activity on Earth
from uranium-238 is only half as much as it originally was
because of its 4.5 billion year half-life. Potassium-40 (half-life
1.25 billion years) is only at about 8% of original activity. But
during the time that humans have existed, the amount of
radiation to which we have been exposed has decreased very
little.
The Earth's lithosphere is composed of seven or eight major
plates (depending on how they are defined) and many minor
plates.Black lines in the following figure denote plate
boundaries.
v
Where the plates meet, their relative motion determines the type
of plate boundary, or fault: convergent, divergent,
or transform. See later text.
The San Andreas Fault is a continental transform fault that
extends roughly 750 miles through California. It forms
the tectonic boundary between the Pacific Plate and the North
American Plate, and its motion is formally described as a
horizontal, right-lateral, strike-slip. In the satellite image
below, arrows show the relative motion of the two plates.
The length of the San Andreas Fault can be compared with two

8. man-made structures: Hadrian’s Wall, a defensive fortification
in Britain begun in 122 AD by the Romans, running a total of 73
miles, and the Great Wall of China, a fortification system built
across the northern borders of China to protect and consolidate
territories of the Chinese empire against nomadic tribes of the
steppe. Begun in the 7th century BC, the wall runs 3889 miles
along an arc that roughly delineates the edge of Mongolian
steppe. Seeing both should be on your “to do” list.
Importantly, mountain building, earthquakes, volcanic
activity, and trench formation occur along plate boundaries.
The relative movement of the plates typically ranges from zero
to ~ 3.9 inches annually.
Tectonic plates are comprised of oceanic and thicker continental
lithospheric crust. Along convergent boundaries, subduction, or
one plate moving under another, carries the lower one down into
the mantle. The material lost is roughly balanced by the
formation of new (oceanic) crust along divergent seams by
seafloor spreading. In this way, the total surface of the
lithosphere remains the same. This aspect of plate tectonics is
referred to as the conveyor belt principle.
Tectonic plates are able to move because the Earth's lithosphere
has greater mechanical strength density than the underlying
asthenosphere asthenosphere. See above. Lateral density
variations in the mantle result in convectionconvection, the
movement caused by the tendency of hotter and therefore less
dense material to rise, and colder, denser material to sink under
the influence of gravity.
Plate movement is thought to be driven by a combination of the
motion of the seafloor away from spreading ridges “ridges” due
to variations topographyand densitychanges in the crust (density
increases as newly formed crust cools and moves away from the
ridge). Tsubduction zoneshe relatively cold, dense oceanic

9. crust is "pulled" down or sinks down into the mantle over the
downward convecting part of the mantle.
What is a volcano?
Earth's volcanoes occur because its crust is broken into rigid
tectonic plates that “float” on a hotter, softer layer in its
mantle.
A volcano is a rupture in the crust of the lithosphere that allows
hot lava, volcanic ash, and gases to escape from a chamber
below the surface of the Earth containing magma, the molten or
semi-molten natural material from which all igneous rocks are
formed (See Lecture 7).
Stratovolcanoes tend to form at subduction zones, or convergent
plate margins, where an oceanic plate slides beneath a
continental plate and contributes to the rise of magma to the
surface. At rift zones, or divergent margins, shield volcanoes
tend to form as two oceanic plates pull slowly apart and magma
effuses upward through the gap. Volcanoes are not generally
found at strike-slip zones, where two plates slide laterally past
each other. “ Hotspot” volcanoes may form where plumes of
lava rise from deep within the mantle to the Earth's crust, far
from any plate margins.
A map showing the divergent plate boundaries (oceanic
spreading ridges) and submerged volcanoes is below.
Large, explosive volcanic eruptions inject water vapor (H2O),
carbon dioxide (CO2), sulfur dioxide (SO2), hydrogen chloride
(HCl), hydrogen fluoride (HF) and ash (pulverized rock
and pumice) into the stratosphere to heights of 10-20 miles
above the Earth's surface. The ash from volcanic eruptions,
plentiful in minerals, enrich the soil after settling to the Earth,

10. resulting in the formation of extensive grasslands in Africa and
North America, and ideal conditions for growing Kona coffee
beans on Hawaii's Kona Coast. A significant consequence of
injections of gases into the atmosphere is the conversion of
sulfur dioxide to sulfuric acid (H2SO4), which condenses
rapidly in the stratosphere to form fine sulfate aerosols. See
later text.
Significant deposits of sulfur around a volcano are common in
the Earth’s crust and upper
mantle. Sulfur, once known as the biblical “brimstone”, is show
below being extracted from the Ljen volcano site in
Indonesia.Sulfur readily comes to the surface because it is a
relatively light element. The reason that it is in gaseous form is
that the melting temperature of S is 115 oC and the vaporization
temperature is 444 oC. So, sulfur is released as a gas by lava
that is typically between 600 and 1200 oC , a temperature
(much) greater than its boiling point.
What is an earthquake?An earthquake (also known as
a quake, tremor or temblor) is the shaking of the surface of the
Earth resulting from a sudden release of energy in
the Earth's lithosphere that creates seismic waves.Earthquakes
can range in size from those that are so weak that they can
hardly be felt to those violent enough to propel objects and
people into the air, and wreak destruction across entire cities.
Seismic activity of an area is a measure of the frequency, type,
and size of earthquakes experienced over a period of time. The
Richter scale is a numerical scale for expressing the magnitude
of an earthquake on the basis of seismograph oscillations. The
more destructive earthquakes typically have magnitudes
between about 5.5 and 8.9. The scale is logarithmic and a
difference of one represents an approximate thirtyfold
difference in magnitude.
At the Earth's surface, earthquakes manifest themselves by
shaking, displacing or disrupting the ground. When

11. the epicenterof a large earthquake is located offshore, the
seabed may be displaced sufficiently to cause a tsunami.
Earthquakes can also trigger landslides and occasionally,
volcanic activity.
A tsunami is a series of waves (see Lecture 13) in a water body
caused by the displacement of a large volume of water,
generally in an ocean or a large lake. Earthquakes, volcanic
eruptions and other underwater explosions above or below water
all have the potential to generate a tsunami.
The Ancient Greek historian Thucydides suggested in his 5th
century BC History of the Peloponnesian Warthat tsunamis were
related to submarine earthquakes. Following from the above, the
energy released by the sudden displacement of two tectonic
plates is imparted to water and the energy is transmitted by
monstrous waves. The Fukushima Daiichi nuclear disaster in
Japan in 2011, mentioned in Lecture 16, was a consequence of
both an “on land” earthquake and a “submarine” earthquake.
How are mountains formed?
Mountain formation refers to geological processes that underlie
the formation of of mountains. These processes are associated
with the large-scale movement of the Earth's crust (tectonic
plates). Folding, faulting, volcanic activity, igneous intrusion
and intrusionandmetamorphismcan all be parts of the process of
mountain building, called orogeny.There are three ways in
which mountains are formed, which correspond to the types of
mountains in question. These are known as volcanic, fold and
block mountains. All of these are the result of plate tectonics,
where compressional forces, isostatic uplift and intrusion of
igneous matter force surface rock upward, creating a landform
higher than the surrounding features.
Over the course of many millions of years, these uplifted
sections are eroded by wind, rain, ice and gravity. These forces
gradually wear down the surface of mountains, causing the

12. surface to be younger than the rocks that form them, and lead to
distinctive formations. Below is The East side of the
Matterhorn in Switzerland, a fold mountain that measures 4,478
meters in height. Worth a trip.
Volcanic mountains are formed when a tectonic plate is pushed
beneath another (or above a mid-ocean ridge or hotspot) and
magma is forced to the surface. When the magma reaches the
surface, it often builds a volcanic mountain, such as a shield
volcano or a stratovolcano. See earlier text. Examples of this
sort of mountains include Mount Fuji in Japan, Mauna Kea in
Hawaii, Nyamuragira in the Democratic Republic of Congo,
Skjaldbreiður in Iceland and Mount Etna in Sicily.At other
times, the rising magma solidifies below the surface and forms
dome mountains, where material is pushed up from the force of
the build-up beneath it. Examples of this formation include
Navajo Mountain in San Juan County, Utah; the Chaitén lava
dome of Chile, Torfajökull in Iceland, and Mount St. Helens in
Washington State.
Fold mountains occur when two tectonic plates collide at a
convergent plate boundary, causing the crust to thicken. This
process forces the less dense crust to float on top of the denser
mantle rocks, with material being forced upwards to form hills,
plateaus or mountains, while a greater volume of material is
forced downward into the mantle.
The Jura Mountains, a series of sub-parallel mountain ridges
located in the Alps, are an example of fold mountains, e.g., the
Zagros mountains, which extend from northern Syria and
southern Turkey to eastern Iran and the Persian Gulf, the
Akwapim-Togo ranges in Ghana and the Appalachians in
eastern United States.
Perhaps most famous is the Himalayan mountain chain, located
between northern India and Nepal. This chain formed as a result
of the collision between the Indian subcontinent and Asia some
25 million years ago, and has given rise to the tallest mountain
in the world, Mt. Everest at 29,029 feet.

13. Satellite image of the Himalayan mountain chain, as imaged by
NASA’s Landsat-7 satellite. Credit: NASA
Block mountains are caused by faults in the crust, a seam where
rocks can move past each other. Also known as rifting, this
process occurs when rocks on one side of a fault rise relative to
the other. The uplifted blocks become block mountains (also
known as horsts) while the intervening dropped blocks are
known as graben (depressed regions).
Examples of this type of terrain can be found in the Upper
Rhine valley, the Vosges mountains in France, the Black Forest
in Germany, and the Vindhya and Satpura horsts in India. The
East African Rift is an active continental rift zone with several
active volcanoes that extends from Eritrea to Mozambique. See
below.
Satellite image of the East African Rift, taken on December
18th, 2002. Credit: NASA/GSFC/METI/Japan Space
Systems/U.S.-Japan ASTER Science TeamAs noted above, the
way in which mountains are shaped over time is by erosion.
This occurs during and after an uplift, where a newly formed
mountainous region is subjected to the effects of wind, water,
ice, and gravity. These forces actively shape the surface of
mountain ranges, wearing down the exposed surfaces,
depositing sediment in alluvial flows, and lead to the formation
of distinctive landforms. Owing to erosion, “younger”
mountain ranges (e.g. the Rockies) are taller than “older”
mountain ranges (e.g., the Appalachians).
Salt in the ocean comes from two sources: runoff from the land
(hills and mountains) and openings in the seafloor.
Rocks on land are the major source of salts dissolved in
seawater. Rainwater that falls on land is slightly acidic, so it
erodes rocks. This releases ions that are carried away to streams
and rivers that eventually feed into the ocean. Many of the

14. dissolved ions are used by organisms in the ocean and are
removed from the water. Others are not removed, so their
concentrations increases over time.
Another source of salts in the ocean is hydrothermal fluids,
which come from vents in the seafloor. Ocean water seeps into
cracks in the seafloor and is heated by magma from the Earth’s
core. The heat causes a series of chemical reactions. The water
tends to lose oxygen, magnesium, and sulfates, and pick up
metals such as iron, zinc, and copper from surrounding rocks.
The heated water is released through vents in the seafloor,
carrying the metals with it. Some ocean salts come from
underwater volcanic eruptions, which directly release minerals
into the ocean.
Two of the most prevalent ions in seawater are sodium (Na+)
and chloride (Cl−). Together, they make up around 85 percent
of all dissolved ions in the ocean. Magnesium ions (Mg+2) and
sulfate ions (SO₄ -2 ) make up another 10 percent of the total.
Other ions are found in very small concentrations.
The concentration of salt in seawater (salinity) varies with
temperature, evaporation, and precipitation. Salinity is
generally low at the equator and at the poles, and high at mid-
latitudes. The average salinity is about 35 parts per thousand.
Stated in another way, about 3.5 percent of the weight of
seawater comes from the dissolved salts.
Are humans made of salt water?
The human body contains many salts, of which NaCl is the
major one, making up around 0.4 per cent of the body's weight
at a concentration pretty much equivalent to that in seawater.
This is not accidental. Life evolved in pools of saline water.
Below is the Grand Prismatic Spring in Yellowstone National
Park in which simple microorganisms thrive and give the Spring
its technicolor.

15. The Midway geyser basin is in the background. A geyser is
a spring characterized by intermittent discharge of water ejected
turbulently and accompanied by steam. The formation of
geysers is due to particular hydrogeological conditions that
exist only in a few places on Earth. Generally all geyser field
sites are located near active volcanic areas, and the geyser
effect is due to the proximity of magma. Surface water works
its way down to an average depth of around 6,600 feet where it
contacts hot rocks. The resultant boiling of the pressurized
water results in the geyser effect of hot water and steam
spraying out of the geyser's surface vent (a hydrothermal
explosion). The most famous geyser in Yellowstone [which has
more geysers (~500) than any place on Earth] is “old Faithful.”
The Yellowstone Caldera is the largest volcanic system in North
America and is only rivalled by the Lake Toba
Caldera on Sumatra. It has been termed a "supervolcano"
because the caldera was formed by exceptionally large
explosive eruptions.
The magma chamber of the volcano that lies under Yellowstone
is estimated to be a single connected chamber, about 37 miles
long, 18 miles wide, and 3 to 7 miles deep. The caldera today
was created by a cataclysmic eruption that occurred ≈
640,000 years ago, which released more than 240 cubic miles of
ash, rock and pyroclastic materials. This eruption was more than
1,000 times larger than Mount St. Helens, an active
stratovolcano located in Skamania County, Washington, in the
Pacific Northwest. Mount St. Helens produced a caldera nearly
5/8 of a mile deep and 45 by 28 miles in area.
The most violent known eruption of Yellowstone, which

16. occurred 2.1 million years ago, ejected 588 cubic miles of
volcanic material. A smaller eruption ejected 67 cubic miles of
material 1.3 million years ago.
Each of the three climactic eruptions released vast amounts of
ash that blanketed much of central North America, falling many
hundreds of miles away. The amount of ash and gases released
into the atmosphere probably caused significant impacts to
world weather patterns and led to the extinction of some
species, primarily in North America.
Geologically then, formation of the mineral Halite took millions
of years of strenuous tectonic activity over which time saltwater
from sea beds was subjected to the combined stresses of
pressure and temperature as layer upon layer were deposited.
RECIPE #2. CLASSICAL EXOTHERMIC REACTION
The “poster child” for exothermic reactions is undoubtedly the
reaction of solid sodium (Na) with gaseous, diatomicchlorine
gas (Cl2). Sodium is a soft metal that must be stored in mineral
oil to prevent reaction with air or water (a). Chlorine is a pale,
yellow-green gas (b). When combined, they form white crystals
of sodium chloride (table salt, c). See below.
The above shows the formation of sodium chloride from sodium
and chloride ions. The reaction is represented with Lewis dot
symbols below.
In the reaction, immense amount of energy in the form of heat

17. and light are given off.
RECIPE #3. WATER CHEMISTRY
Sodium hydroxide, also known as lye and caustic soda, is an
inorganic compound with the formula NaOH. It is a white,
solid, ionic compound consisting of sodium cations Na⁺ and
hydroxide anions OH⁻ .
Hydrochloric acid, also known as muriatic acid, is a
colorless inorganic chemical system with the formula HCl
consisting of an aquous solution of hydrogen cations (H+) and
chlorine anions (Cl−). Hydrochloric acid has a
distinctive pungent smell.
When sodium hydroxide is dissolved in an aqueous solution of
hydrochloric acid, the following reaction takes place:
NaOH + HCl → H2O + NaCl
Or, more precisely,
Na+(aq) + OH –(aq) + H+(aq) + Cl− (aq) →
H2O(l) + NaCl(s)
where aq denotes the aqueous phase, l the liquid phase and s the
solid phase.
An acid–base (or neutralization) reaction is a chemical
reaction that occurs between an acid and a base.
The first scientific concept of acids and bases was provided
by Lavoisier around 1776. Since Lavoisier's knowledge
of strong acids was mainly restricted to oxoacids, such as nitric
acid (HNO3 ) and sulfuric acid (H2SO4), which contain central
atoms in high oxidation states surrounded by oxygen, and since

18. he was not aware of the composition of the acidsHF, HCl, HBr,
and HI, he defined acids in terms of their containing oxygen,
which he named from Greek words meaning "acid-former" (from
the Greek οξυς (oxys) meaning "acid" or "sharp" and γεινομαι
(geinomai) meaning "engender").
The Lavoisier definition held for over 30 years (until 1810)
when Humphry Davy described his experiments on the lack of
oxygen in H2S, H2Te, HF, HCl, HBr, and HI. Davy did not
advance a new theory, however, concluding that "acidity does
not depend upon any particular elementary substance, but upon
peculiar arrangement of various substances".
One notable modification of oxygen theory was provided
by Jöns Berzelius, who stated that acids are oxides of nonmetals
while bases are oxides of metals.
In 1838, Justus von Liebig proposed that an acid is a hydrogen-
containing compound whose hydrogen can be replaced by a
metal. This redefinition was based on his extensive work on the
chemical composition of organic acids, shifting the emphasis
from oxygen-based acids to hydrogen-based acids. Liebig's
definition, while completely empirical, remained in use for
almost 50 years.
The first modern definition of acids and bases in molecular
terms was devised by Svante Arrhenius (1859-1927),
a Swedish chemist. Recall from Lecture 4 that Arrhenius in
1884 proposed that, even in the absence of an electric current,
solutions of salts contained ions. That is, he proposed that solid
crystalline solids, when dissolved in water, dissociated into
pairs of charged particles (ions), and that chemical reactions in
solution involved reactions between ions.
A hydrogen theory of acids followed from his 1884 work
with Friedrich Wilhelm Ostwald in which they established the

19. presence of ions in aqueous solution. The Nobel Prize in
Chemistry was awarded to Svante August Arrhenius in 1903 "in
recognition of the extraordinary services he has rendered to the
advancement of chemistry by his electrolytic theory of
dissociation”, the same year Henri Becquerel, Pierre Curie
and Marie Curie (née Sklodowska) received the Nobel Prize in
Physics.
An Arrhenius acid is a substance that dissociates in water to
form hydrogen ions (H+). That is, an acid increases the
concentration of H ions in aqueous solution.
This causes the protonation of water, or the creation of
the hydroniumion (H3O+) ion, also called the oxonium ion.
Today, the symbol H+ is interpreted as a shorthand for H3O+,
because it is now known that a bare proton does not exist as a
free species in aqueous solution.
An Arrhenius base is a substance that dissociates in water to
form hydroxideions (OH−), that is, a base increases the
concentration of OH− ions in an aqueous solution.
The Arrhenius definitions of acidity and alkalinity are restricted
to aqueous solutions, and refer to the concentration of the
solvent ions. Under this definition, H2SO4 and HCl dissolved in
toluene are not acidic, and molten NaOH and solutions of
calcium amide in liquid ammonia are not alkaline. This led to
the development of the Bronsted-Lowry theory and subsequent
Lewis theory to account for these non-aqueous exceptions. See
text below.
Overall, to qualify as an Arrhenius acid, upon the introduction
to water, the chemical must either cause, directly or otherwise:
an increase in the aqueous hydronium concentration, or a
decrease in the aqueous hydroxide concentration.
Conversely, to qualify as an Arrhenius base, upon the
introduction to water, the chemical must either cause, directly
or otherwise:
a decrease in the aqueous hydronium concentration, or an

20. increase in the aqueous hydroxide concentration.
The reaction of an acid with a base is called
a neutralizationreaction. The products of this reaction are
always a saltand water, regardless of which acid or which base
are involved in the neutralization reaction.
acid + base → salt + water
In this representation, an acid–base neutralization reaction is
characterized as a double-replacement reaction. For example,
the reaction of hydrochloric acid, HCl, with sodium hydroxide,
NaOH, solutions produces a solution of sodium chloride, NaCl,
and some additional water molecules.
HCl (aq) + NaOH (aq) → NaCl (aq) + H2O (l)
Though all three substances, HCl, NaOH and NaCl, are capable
of existing as pure compounds, in aqueous solutions they are
fully dissociated into the aquatedions H+, Cl−, Na+ and OH−,
hence the notation HCl (aq) and NaOH (aq).
Following the discovery of the proton by Rutherford in 1919, a
new, more generalized definition of acids and bases was
proposed in 1923 almost simultaneously by J.M.
Brønsted and T.M. Lowryin order to resolve the various
difficulties in the hydrogen–hydroxide ion definitions of acids
and bases. The Brønsted–Lowry definitionof acids and bases
has had far-reaching consequences in understanding a wide
range of phenomena and in the stimulation of much
experimental work.
The definition is as follows: an acid is a species having a
tendency to lose a proton, and a base is a species having a
tendency to gain a proton. The term proton means the species
H+ (the nucleus of the hydrogen atom) rather than the actual
hydrogen ions that occur in various solutions. The definition is
thus independent of the nature of the particular solvent.

21. The use of the word species rather
than substance or molecule implies that the
terms acid and base are not restricted to uncharged molecules
but can also apply also to positively or negatively charged ions.
This extension, one of the important features of the Brønsted–
Lowry definition, can be summarized by the equation :
A ⇄ B + H+
in which A and B together are a conjugate acid–base pair. In
such a pair A must have one or more positive charges (or, one
or more less negative charges) than B, but there is no other
restriction on the sign or magnitude of the charges.
Several examples of conjugate acid–base pairs are given in the
table.
Examples of conjugate acid-base pairs
acid
base
acetic acid, CH3CO2H
acetate ion, CH3CO2−
bisulfate ion, HSO4−
sulfate ion, SO42−
ammonium ion, NH4+
ammonia, NH3
ammonia, NH3
amide ion, NH2−
water, H2O
hydroxide ion, OH−
hydronium ion, H3O+
water, H2O
A number of points about the Brønsted–Lowry definition need
to be stressed:
1. As mentioned above, this definition is independent of the
solvent. The ions derived from the solvent (H3O+ and OH− in

22. water and NH4+ and NH2− in liquid ammonia) are not accorded
any special status but appear as examples of acids or bases in
terms of the general definition.
2. In addition to the familiar molecular acids, two classes
of ionic acids emerge from the new definition. The
first comprises anions derived from acids containing more than
one acidic hydrogen, e.g., the bisulfate ion (HSO4−) and
primary and secondary phosphate ions derived from phosphoric
acid (H3PO4).
A second and more interesting class consists of positively
charged ions (cations), such as the ammonium ion (NH4+),
which can be derived by the addition of a proton to a molecular
base, in this case ammonia (NH3). The hydronium ion (H3O+),
which is the hydrogen ion in aqueous solution, also belongs to
this class. The charge of these ionic acids must always be
balanced by ions of opposite charges, but these oppositely
charged ions usually are irrelevant to the acid–base properties
of the system.
For example, if sodium bisulfate (Na+HSO4−) or ammonium
chloride (NH4+Cl−) is used as an acid, the sodium ion (Na+)
and the chloride ion (Cl−) contribute nothing to the acidic
properties and could equally well be replaced by other ions,
such as potassium (K+) and perchlorate (ClO4−), respectively.
3. Molecules such as ammonia and organic amines are bases by
virtue of their tendency to accept a proton. With metallic
hydroxides such as sodium hydroxide, on the other hand, the
basic properties are due to the hydroxide ion itself, the sodium
ion serving merely to preserve electrical neutrality. Moreover,
not only the hydroxide ion but also the anions of other weak
acids (for example, the acetate ion) must be classed as bases
because of their tendency to form an acid by accepting a proton.

23. Formally, the anion of any acid might be regarded as a base, but
for the anion of a very strong acid (the chloride ion, for
example) the tendency to accept a proton is so weak that its
basic properties are insignificant and it is inappropriate to
describe it as a base.
Similarly, all hydrogen compounds could formally be defined as
acids, but in many of them (for example, most hydrocarbons,
such as methane (CH4 ) the tendency to lose a proton is so
small that the term acidwould not normally be applied to them.
4. Some species, including molecules as well as ions, possess
both acidic and basic properties. Such materials are said to be
amphoteric . Both water and ammonia are amphoteric, a
situation that can be represented for water by the following
equation:
H2O + H2O ⇌ H3O+ + OH−
This equation is demonstrated in the images below:
Here, one molecule of water acts as an acid, donating an H+ and
forming the conjugate base, OH−, and a second molecule of
water acts as a base, accepting the H+ ion and forming the
conjugate acid, the hydronium or oxonium ion, H3O+. The
amphoteric properties of water are particularly important in
determining its properties as a solvent for acid–base reactions.
Another example is the secondary phosphate ion, HPO42−,
which can either lose or accept a proton, according to the
following equations:
HPO42− ⇄ PO43− + H+ and HPO42− +
H+ ⇄ H2PO4−.
5. The equation A ⇄ B + H+, used in the Brønsted–Lowry
definition, does not represent a reaction that can be observed in
practice, since the free proton, H+, can be observed only in
gaseous systems at low pressures.

24. In solution, the proton always is attached to some other
species, commonly a solvent molecule. Thus in water the ion
H3O+ consists of a proton bound to a water molecule. For this
reason all observable acid–base reactions in solution are
combined in pairs, with the result that they are of the form
A1 + B2 ⇄ B1 + A2.
The fact that the process A ⇄ B + H+ cannot be observed does
not imply any serious inadequacy of the definition. As we shall
see in Lecture 18, a similar situation exists with the definitions
of oxidizingandreducing agents, which are defined respectively
as species having a tendency to gain or lose electrons, even
though one of these reactions never occurs alone and free
electrons are never detected in solution (any more than free
protons are).
The dissociation of acids and bases is characterized by a
defined signature, the pH.In Chemistry, pH is a scale used to
specify how acidic or basic (or alkaline) an aqueous solution is.
Mathematically, is defined as the negative logarithmicvalue
(base 10) of the Hydrogen ion concentration [H+],
pH = − log10 [H+]
Following from this definition, a lower pH indicates a higher
concentration of hydrogen ions. Acidic solutions have a lower
pH, while basic solutions have a higher pH.
At room temperature (25 °C or 77 °F), amphoteric pure water is
neither acidic nor basic and has a pH of 7. At 25 °C, solutions
with a pH less than 7 are acidic, and solutions with a pH greater
than 7 are basic. This neutral value of the pH depends on the
temperature, being lower than 7 if the temperature increases.
The pH of some common substances follows:

25. Given below are some representative examples of acid-base
reactions.
A prime example of acid-base chemistry is stomach acid. The
pH of the stomach juice generally lies within a range of pH 1.0-
2.5. Stomach acid alters the natural folded shapes of protein
molecules, allowing them to be broken down by digestive
enzymes.
Though stomach acid is extremely useful in this manner, it can
also be harmful if unregulated, since it can destroy the protein
molecules in the stomach tissue itself. To prevent this from
happening, the interior of the stomach is coated with a layer of
cells known as gastric mucosa, which insulates the stomach wall
from acidic gastric juices. Cells beneath the gastric mucosa are
activated via stimuli of taste, smell and histamine (a type of
signaling molecule) that results in parietal cells releasing HCl
into the stomach. Conditions such as hyperacidity, where there
is excessive amounts of acid secreted into the stomach, and
peptic ulcers, which are sores resulting from bacterial
infections, can be regulated by medications that block histamine
from signaling the parietal cells. Some common ingredients
used in these medications include cimetidine, famotidine, and
ranitidine.
Another example of acid-base reactions is the effect of pH on
DNA. The formation of DNA occurs readily at a pH of 7.
Altering the pH level of a solution containing the double-helical
DNA can destabilize the DNA double helix. In a solution with
double-helical DNA and a concentrated base (such as OH-), the
DNA will begin to dissociate into its corresponding single
strands when pH approaches 9.0. This is a result of the
hydroxide ions (OH− ) and their interaction with DNA base
pairs, removing specific protons. Similarly, when the pH of this
solution drops too low (below 5.0), the DNA double helix is
destabilized. This is because some of the hydrogen bond
acceptors become protonated and can no longer participate in

26. hydrogen bonding, so the double helix separates. Both examples
show how altering the pH of DNA can disrupt its double-helical
structure.
In the above text I described the weathering and erosion of
mountain landscapes.Weathering is not the same as erosion,
although they are sometimes confused. Weathering processes do
not involve the transport of matter. Weathering is the breaking
up of rock into small pieces. There are two types of weathering
physical ormechanical
chemical
Physical weathering has taken place in limestone landscapes
,such as the Pennines of Yorkshire, England. An example is
“freeze–thaw” where water soaks into small fissures and cracks
and expands when it freezes in the winter, physically breaking
up the limestone. BTW, this is the origin of “potholes” in some
Chicago streets.
Chemical weathering involves the decomposition of rocks due
to chemical reactions between minerals such as calcite with
water and gases in the atmosphere [e.g. carbon dioxide (CO2)
and sulfur dioxide (SO2)]. Chemical weathering is the most
important way that limestones are broken down.
Calcite is a carbonate mineral and the most stable polymorph of
calcium carbonate (CaCO3) The Mohs scale of mineral
hardness, based on scratch hardness comparison, gives the value
3 for "calcite" (Diamond is 10). The solution of soluble
minerals is particularly important in limestone landscapes.
Granite chemically weathers to form china clay.
Chemical weathering can be caused by rain water.
Rain has a major impact on karst scenery through chemical
weathering.
“Ordinary” rain is naturally acidic because it contains dissolved

27. carbon dioxide that forms weak carbonic acid (H2CO3). When
this weak acid (pH ~ 5.5) comes into contact with calcite, the
limestone begins to dissolve. The sequence of events follows:
1. Droplets of rain water (H2O) in the clouds dissolve carbon
dioxide (CO2) in the atmosphere.
2. When combined, these form carbonic acid (H2CO3).
3. The slightly acidic rain then falls onto the ground.
4. The rain soaks into the soil or flows over the exposed
limestone (CaCO3).
It may become even more acidic if it soaks into soil where there
are naturally occurring acids from plant material or minerals
such as pyrite. Also known as fool's gold, pyrite is an iron
sulfide with the chemical formula FeS2.See Lecture 2.
An acid-base reaction takes place when the rain (i.e. carbonic
acid) interacts with limestone (i.e. calcite).
The acid H2CO3 and the CaCO3 combine to form two ions of
HCO3-1 and Ca+2.
The calcite is converted to calcium bicarbonate, Ca(HCO3)2,
which is soluble in water and is washed away by the rain.
Fifteen million years ago, the Earth entered a phase of slow and
continuous cooling. A current theory for the cooling was the
formation of major mountain ranges, like the Himalayas.
According to this theory, when the Indian and Asian tectonic
plates collided, it brought fresh rocks up to the surface. The
new rocks were more vulnerable to weathering via carbonic acid
(H2CO3) as described above. Soluble carbonates were washed
down the mountain side to the sea and sediments began to
accumulate, thus capturing and storing CO2. Carbon dioxide is
a “greenhouse gas,” so its removal from the atmosphere caused
a gradual cooling of the Earth. The long-term change in the
temperature of the Earth was significant. See the panel in the
lower right-hand corner of the figure below:

28. Climate change during the last 65 million years.
Chemical weathering can also be caused by acid rain.
The problem of acid rain began with the Industrial Revolution
(from about 1760 to 1840) and increased in the 20th century.
Pollutants were created which escaped into the atmosphere and
were dissolved in rain water. The main pollutant is sulfur
dioxide (SO2), but nitrogen oxides are also present.
In simple terms, acid rain is a weak sulfuric acid (H2SO4), and
this is the most significant cause of chemical weathering.
Following is the sequence of events:
1. Rain water (H2O) in clouds dissolves some of the SO2, a
pollutant from industrial manufacturing.
2. This makes weak sulfuric acid (H2SO4).
3. The acidic rain then falls on to the ground.
4. The rain soaks into the soil and porous limestone deposits
and wets rocks containing the mineral calcite (CaCO3).
5. An acid-base reaction takes place. Acid rain (H2O, with a %
of H2SO4) and limestone (CaCO3) react, causing the formation
of water (H2O), carbon dioxide (CO2) and soluble calcium
sulfate (CaSO4).
6. The water is added to the rain and is lost when it soaks away
or evaporates, the carbon dioxide is lost to the atmosphere and
calcium sulfate is lost when it dissolves in water and is washed
away.
Chemical weathering in limestone areas causes special
topographical solution features to form, known as karst. Karst
features include limestone pavement, sinkholes (dolines) and
fissures in limestone called clints, and groves in the limestone
called karren.

29. Limestone pavement, Malham Cove, North Yorkshire, England.
The clints, in the foreground, are formed by the solvent action
of rainwater on joints in the limestone.
© NERC P005457
A stream flows into a sinkhole in the limestone in Cumbria,
England. Limestone rocks dissolve when attacked by rainfall or
groundwater that is acidic.
© NERC P005101
Karren grooves on clint surfaces between joint controlled
grikes; near Orton, Penrith.
© NERC P005458
Weathering and erosion cause the disfigurement of statues
exposed to the elements. The statues on Easter Island,
are eroding, principally due to weathering.
Statues outdoors, subject to the combined effects of weathering
and chemical erosion, deteriorate significantly.
When I first visited Venice, Italy in the 1960s, this deterioration
was already very striking, caused by pollutants (CO2, SO2)

30. released into the atmosphere from nearby coal-powered plants.
Chemical and
Biological weapons
Can they be eliminated or controlled?
T
he Syrian government’s use of nerve gas on rebel-
controlled Damascus neighborhoods this summer
focused renewed attention on the threat posed by
chemical and biological weapons. The attacks, which
killed up to about 1,400, led President Obama to threaten
military
retaliation. Syrian President Bashar al-Assad responded by
agreeing
to destroy his chemical arsenal. Chemical weapons have been
out-
lawed since 1928, after the world saw the horrors of their effect
in world war I. After Iraq used chemical weapons to kill tens of

31. thousands of Iranians and Iraqi Kurds in the 1980s, a 1993
interna-
tional accord strengthened enforcement of the ban. The Syrian
gas
attacks have spurred debate over whether chemical weapons are
worse than conventional arms. meanwhile, biological weapons
also
are outlawed, but some experts fear they could be used by
terrorists.
A student practices handling simulated waste at the
Chemical Demilitarization Training Facility at the
Army’s Aberdeen Proving Ground in Maryland. Most
of the world’s chemical weapons have been destroyed
under a 1993 treaty. However, several non-
participants in the treaty, including North Korea,
maintain chemical weapons stockpiles.
CQ Researcher • Dec. 13, 2013 • www.cqresearcher.com
Volume 23, Number 44 • Pages 1053-1076
RECIPIENT Of SOCIETY Of PROfESSIONAL JOURNALISTS
AwARD fOR
EXCELLENCE � AmERICAN BAR ASSOCIATION SILvER
GAvEL AwARD
I
N

32. S
I
D
E
THE ISSUES ..................1055
BACKGROUND ..............1062
CHRONOLOGY ..............1063
CURRENT SITUATION ......1068
AT ISSUE......................1069
OUTLOOK ....................1071
BIBLIOGRAPHY ..............1074
THE NEXT STEP ............1075
THISREPORT
Published by CQ Press, an Imprint of SAGE Publications, Inc.
www.cqresearcher.com
1054 CQ Researcher
THE ISSUES

33. 1055 • Are chemical weaponsworse than other weapons of
war?
• Are biological weapons a
serious threat to the United
States?
• Can the world rid itself of
chemical and biological
weapons?
BACKGROUND
1062 Primitive AttemptsChemical and biological
weapons were used in
ancient times.
1065 World War ILethal gas attacks led to a
postwar ban on chemical
weapons.
1065 World War IIThe Geneva Protocol aimed
to ban chemical weapons.
CURRENT SITUATION
1068 Syria DisarmsPresident Assad agreed to
destroy his chemical
weapons.
1068 Other EffortsSeveral other nations have
agreed to destroy their
chemical weapons.
1070 Bioweapons ThreatThe United States has several
programs to protect against
biological attacks.

34. OUTLOOK
1071 Complacency?Historical amnesia could lead
to new threats, some experts
warn.
SIDEBARS AND GRAPHICS
1056 Most Chemical WeaponsHave Been Destroyed
Russia and the U.S. have the
largest remaining stockpiles.
1057 North Korea Said to HaveLarge Stockpile
China, Iran and Israel also
may have chemical weapons.
1058 From Anthrax to MustardGas
Chemical and biological
weapons have various
characteristics.
1060 World War I Saw DeadliestChemical Attacks
Iraqi gas attacks killed or
wounded up to 60,000 people
in the 1980s.
1063 ChronologyKey events since 1915.
1064 Biological Weapons vs.Natural Occurrences
Sometimes it’s difficult to tell
the difference.
1067 And the Nobel PeacePrize Goes to. . . .
The Organisation for the Pro-
hibition of Chemical weapons
won the 2013 award.

35. 1069 At Issue:Does chemical weapons use
warrant military intervention?
FOR FURTHER RESEARCH
1073 For More InformationOrganizations to contact.
1074 BibliographySelected sources used.
1075 The Next StepAdditional articles.
1075 Citing CQ ResearcherSample bibliography formats.
CHEmICAL AND BIOLOGICAL wEAPONS
Cover: U.S. Army Chemical Materials Activity
MANAGING EDITOR: Thomas J. Billitteri
[email protected]
ASSISTANT MANAGING EDITOR: Kathy Koch,
[email protected]
SENIOR CONTRIBUTING EDITOR:
Thomas J. Colin
[email protected]
CONTRIBUTING WRITERS: marcia Clemmitt,
Sarah Glazer, Kenneth Jost, Peter Katel,
Reed Karaim, Barbara mantel, Tom Price,
Jennifer weeks
SENIOR PROJECT EDITOR: Olu B. Davis
FACT CHECKERS: michelle Harris,
Nancie majkowski

36. An Imprint of SAGE Publications, Inc.
VICE PRESIDENT AND EDITORIAL DIRECTOR,
HIGHER EDUCATION GROUP:
michele Sordi
EXECUTIVE DIRECTOR, ONLINE LIBRARY AND
REFERENCE PUBLISHING:
Todd Baldwin
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Volume 23, Number 44
Dec. 13, 2013 1055www.cqresearcher.com
Chemical and Biological weapons

38. THE ISSUES
A s soon as the firstrockets explodedaround 2:45 a.m. on
Aug. 21 in the Damascus sub-
urb of Ghouta, in Syria, res-
idents began experiencing
horrific suffering: frothing at
the mouth, fluid coming out
of the eyes, convulsions and
suffocation. 1
Two hours later another
round of rockets landed in
the nearby neighborhood of
moadamiya. “we were pray-
ing in the mosque near the
Turbi area, 400 meters away,”
an eyewitness later told the
international advocacy group
Human Rights watch. “we
heard the strike and went to
the site to help the wound-
ed . . . when we got there
someone was screaming,
‘Chemical! Chemical!’ People
covered their faces with shirts
dunked in water. we didn’t
smell anything, but . . . if
anyone entered the building
where the rocket fell, they
would faint.” 2
Human Rights watch and
United Nations inspectors later said the
rockets carried sarin nerve gas. One
drop of sarin fluid can make a per-
son ill. 3 Estimates of the number of

39. Syrians who died in the attacks range
from the U.S. government’s figure of
more than 1,400 — including 426 chil-
dren and other civilians — to 355, re-
ported by médicins Sans frontièrs (Doc-
tors without Borders), the international
humanitarian organization. 4
Global outrage over the attacks
sparked a renewed debate about how
the world community should respond
to chemical and biological weapons,
and whether they are really any worse
— morally or in their lethal effect —
than conventional wartime arms. Both
types of weapons kill people, some
observers say, so making a distinction
is meaningless. But others say chem-
ical weapons are unique, in that they
target defenseless civilians.
The rockets fired on Damascus had
almost certainly been fired by the gov-
ernment of President Bashar al-Assad
against rebel forces in Syria’s ongoing
civil war, according to Human Rights
watch and the U.S. and french gov-
ernments. Although chemical weapons
such as sarin long have been prohibit-
ed by international treaty, at the time
of the attacks Syria was one of five
nations that hadn’t signed the 1993
Convention on the Prohibi-
tion of Chemical weapons,

40. known simply as the Chem-
ical weapons Convention
(CwC), which went into ef-
fect in 1997.
Although some evidence
indicated that Syria had used
chemicals weapons on a small-
er scale earlier in the war, the
Ghouta attack represented
the first time a nation had
launched a significant chem-
ical weapons attack since
Iraqi leader Saddam Hussein
used them against Iran and
Iraqi Kurds in the 1980s.
The United States and much
of the global community quick-
ly condemned Syria’s action.
“This attack is an assault on
human dignity,” said President
Obama, adding that he would
ask Congress to support a
limited military strike against
Syrian forces in response.
“Here’s my question for every
member of Congress and
every member of the global
community: what message
will we send if a dictator can
gas hundreds of children to
death in plain sight and pay
no price?” 5
Obama’s comments were intended

41. to reinforce a “red line” he had drawn
earlier insisting that chemical weapons
were outside of the acceptable inter-
national norms of behavior, even in
war. But some critics of Obama’s com-
ment questioned the wisdom of taking
a position that could require a military
response.
“The lesson learned is: Never an-
chor yourself by drawing red lines
because then you take away other op-
tions,” says Gary Guertner, a profes-
sor at the University of Arizona in Tuc-
son and former chairman of the Policy
and Strategy Department at the U.S.
Army war College.
BY REED KARAIM
A
P
P
ho
to
/S
ha
am
N
ew
s

42. N
et
w
or
k
Civilians lie in a makeshift mortuary after being killed in a
sarin gas attack on Damascus, Syria, on Aug. 21, 2013.
Syrian forces under President Bashar al-Assad launched
the attack against rebel forces in the city, according to
Human Rights Watch and the U.S. and French
governments. More than 1,400 people were killed,
including hundreds of women and children,
according to the U.S. government.
1056 CQ Researcher
Others observers, however, sug-
gested Obama should have acted even
more forcefully. “when it comes to
saying this is horrible, we need to con-
tain it. we need to draw the line,” says
michael Rubin, a resident scholar at
the conservative American Enterprise
Institute and a former Pentagon offi-
cial. “The president could have acted
symbolically by immediately targeting
the units that used the weapons.”
Obama asked Congress to approve

43. limited strikes on Syria in retaliation,
but lawmakers from both parties indi-
cated that Congress might not approve
more military action in the middle East.
Nevertheless, facing even the possibil-
ity of a U.S. military strike, Syria agreed
to sign the 1993 convention and open
its chemical weapons arsenal for im-
mediate inspection and dismantling.
(See “Current Situation,” p. 1068.)
Although the deal, largely brokered
by Syria’s key ally, Russia, meant the
U.S. Congress never had to vote on
whether to authorize the use of force,
the debate over the threat represent-
ed by chemical and biological weapons
— and how the world should respond
to their use — has continued.
Chemical weapons have been con-
sidered unacceptable by the global
community since the widespread use
of poison gases in world war I killed
or wounded thousands of soldiers.
(See “Background,” p. 1065.) The
Geneva Protocol banned them in 1928,
and although scattered exceptions have
occurred, the convention and the
even stronger 1993 accord have large-
ly kept chemical weapons off the
world’s battlefields.
“It’s a real robust taboo that has de-
veloped over time,” says Richard Price,
a professor of political science at the

44. University of British Columbia in van-
couver and the author of The Chem-
ical Weapons Taboo. “what you saw
in Syria, it’s the first time they’ve been
used in 25 years. That’s a remarkable
record for a weapon of warfare.”
Biological weapons, which use dis-
ease microbes or toxins to attack their
victims, have received less attention but
also are outlawed by an international
treaty, the 1972 Biological weapons Con-
vention, which went into force in 1975.
Although biological agents rarely have
been used in warfare, some analysts
consider them a greater potential threat,
especially as a terrorist weapon.
Chemical and biological weapons
often are discussed together, but
weapons experts point out they re-
quire different resources to build and
pose different challenges to find and
neutralize. Building a chemical weapons
arsenal requires a significant industrial
capacity, the ability not only to manu-
facture large amounts of the chemical
agents but also to load them in rock-
ets or shells that can be fired at the
enemy. The large-scale industrial plants,
resources and personnel required mean
CHEmICAL AND BIOLOGICAL wEAPONS
Most Chemical Weapons Have Been Destroyed

45. Nearly 82 percent of the world’s declared chemical weapons
have
been destroyed since the Chemical Weapons Convention went
into
effect in 1997. Russia has the world’s largest remaining
stockpile of
chemical weapons, about three times more than the United
States. At
least six countries are thought to have had or to still have
undeclared
chemical weapons.
Note: Japan left 350,000 chemical munitions on Chinese soil
during World War II.
It is working with China to dispose of those weapons.
* When Iraq joined the Chemical Weapons Convention in 2009,
it said an unknown
quantity of chemical agents remained in bunkers that were
bombed in 2003.
** A metric ton is 2,204.6 pounds.
Sources: Organisation for the Prohibition of Chemical Weapons;
“Chemical and
Biological Weapons Status at a Glance,” Arms Control
Association, October 2013,
www.armscontrol.org/factsheets/cbwprolif, and telephone
conversations with Arms
Control Association personnel
Amount of Chemical Weapons Declared,
Destroyed and Remaining, by Country
(as of October, 2013)

46. Metric Tons** Percent Metric Tons**
Country Declared Destroyed (as of) Remaining
Albania 16 100% (2007) 0
South Korea undisclosed 100% (2008) 0
India 1,000+ 100% (2009) 0
United States 31,500 90% (intends by 3,150
2023)
Russia 40,000 76% (pledged by 9,600
2015-20)
Libya 26.3 85% (planning by 3.95
end of 2016)
Iraq unknown* 0% NA
Syria 1,300 In process NA
(first half of 2014)
Dec. 13, 2013 1057www.cqresearcher.com
chemical weapons are harder to hide
than biological weapons.
The 1993 Chemical weapons Con-
vention established an inspection pro-
cedure for chemical weapons sites and
timetables for destruction of chemical
arsenals. Nearly all nations with sig-
nificant stockpiles of such weapons,

47. including the United States and Rus-
sia, have been proceeding with their
destruction. (See chart, p. 1056.) The
Organisation for the Prohibition of
Chemical weapons, a Hague-based
agency that oversees implementation
of the convention, says 81.7 percent
of the world’s declared chemical
weapons have been destroyed. 6
Biological weapons, such as anthrax
or smallpox, can be grown in a lab, so
they have a smaller “footprint” than chem-
ical weapons, making them easier to
hide. But many of the deadliest pathogens
exist only in a limited number of re-
search laboratories around the world.
Thus, they are less available than the
basic materials of chemical weapons.
The United States and other nations
have boosted efforts to secure sup-
plies of dangerous pathogens in re-
cent years. The 1972 Biological
weapons Convention, however, does
not have the same strong inspection
mechanisms as the Chemical weapons
Convention, leading to greater con-
cerns that these deadly agents could
be secretly grown and weaponized.
As the world weighs options for
dealing with chemical and biological
weapons, here are some of the ques-
tions under discussion:

48. Are chemical weapons worse than
other weapons of war?
Chemical weapons are one of the
few categories of weapons specifically
banned through international treaty. 7
But even during world war I, when
they were used widely by both sides,
they accounted for a relatively small
percentage of overall casualties.
Up to 100,000 soldiers were killed
by gas attacks in world war I — less
than 1 percent of the war’s fatalities, and
more than 1 million were wounded by
gas, or about 2 percent of the total;
many were blinded. 8 In the Syrian con-
flict, 70 to 100 times as many people
have died from conventional weapons
— 105,000 to 150,000 deaths — as died
in the gas attacks. 9
Such disparities lead some analysts
to question whether chemical weapons
should be considered worse than other
weapons. “There’s a sense people have
that somehow chemical weapons are
worse — more horrifying. But if you
look at it coolly and rationally, it’s not
obvious that they are worse than shelling
or guns, which have killed many more
people,” says Dominic Tierney, a po-
litical science professor at Swarthmore

49. College in Pennsylvania.
Regardless of the casualty count,
other analysts believe chemical
weapons have characteristics that make
them especially brutal.
Sources: Organisation for the Prohibition of Chemical Weapons;
“Chemical and
Biological Weapons Status at a Glance,” Arms Control
Association, October 2013,
www.armscontrol.org/factsheets/cbwprolif, and telephone
conversations with Arms
Control Association personnel
North Korea Said to Have Large Stockpile
At least six countries are thought to have had or to still have
unde-
clared chemical weapons, including North Korea, which is
believed
to have a large stockpile developed during a long-standing
program.
Countries Suspected of Having Chemical Weapons
China — The United States alleged in 2003 that China had an
“advanced chemical weapons research and development
program,”
but a 2010 State Department report said there was insufficient
evidence to confirm China’s previous or current activities.
Egypt — Allegedly stockpiled chemical weapons and used
them against Yemen in 1963-67; has never signed the Chemical
Weapons Convention (CWC).

50. Iran — Denounces possession of chemical weapons; recent
State Department assessments said Iran is “capable of
weaponiz-
ing” chemical agents in a variety of delivery systems.
Israel — Believed to have had an offensive chemical weapons
program in the past, but there is no conclusive evidence of an
ongoing program; has not ratified the CWC.
North Korea — Has a “long-standing CW program” and a
large stockpile of weapons, according to a 2012 U.S.
intelligence
assessment.
Sudan — Unconfirmed reports say that Sudan developed and
used chemical weapons in the past; United States bombed what
was alleged to be a chemical weapons factory in 1998. A 2005
State Department report questions whether Sudan was ever
involved in chemical weapons manufacture.
1058 CQ Researcher
“There is something unique about
chemical weapons” because of “who
they most effectively destroy: babies
sleeping in their cribs and innocent
civilians,” says Greg Thielmann, a se-
nior fellow at the washington-based
Arms Control Association, which sup-
ports effective arm control policies.
“And the people they’re least likely
to destroy are prepared soldiers be-
cause soldiers can protect themselves

51. against chemical weapons much more
easily than they can against high ex-
plosives.”
Rubin, the American Enterprise In-
stitute scholar, notes that chemical
weapons are less accurate than con-
ventional weapons. “Conventional mu-
nitions have become more precise over
time — more lethal while also more
precise,” he says. “The problem with
chemical weapons is that they’re no-
toriously imprecise — they’re at the
mercy of the wind, for example.” That
means they can only be counted on
to sow terror or kill indiscriminately,
he adds.
CHEmICAL AND BIOLOGICAL wEAPONS
A wide range of chemical and biological weapons have
beendeveloped in the past century, although only a
limitednumber have been used on the battlefield. The earliest
poison gases deployed in world war I were easily countered
by simple gas masks, but before the war’s end scientists had
developed mustard gas, a blistering agent effective enough that
it remained in chemical arsenals into the 21st century.
Chemical and biological weapons are outlawed today under
international treaties. much of the world’s chemical arsenal has
already been destroyed, and biological weapons are considered
unlikely to be used by nations because of their unpredictable
nature. Still, some countries, including the United States and
Russia, are still in the process of destroying their chemical ar-
senals, and it is possible other hidden stockpiles exist. Both

52. chemical and biological weapons are also considered attractive
to terrorist groups because of the weapons’ ability to cause
widespread destruction and panic.
Here are some of the main chemical and biological agents
that have been or could be used in weapons: 1
• Mustard gas — Nearly odorless and hard to detect, sul-
fur mustard gas damages the skin and mucous membranes on
contact. It is an organic chemical compound that derives its
name from a faint smell of the mustard plant that sometimes
accompanies it. Exposure can come through the skin, eyes,
lungs or by drinking contaminated water. Death often occurs
when the lungs fill up with fluid after their linings are de-
stroyed. No antidote exists for mustard gas.
• Sarin — One of the first “nerve agent” chemical weapons,
sarin is an oily liquid that evaporates quickly into a vaporous
gas. It can cause convulsions, constriction of the chest and suf-
focation. It interrupts the operation of an enzyme that works
as an “off switch” for muscles and glands, which then become
constantly stimulated. Exposure by inhalation or touch can be
deadly. Even a drop of sarin on the skin can cause serious in-
jury. Antidotes exist, but must be administered quickly.
• VX — The most potent of all nerve agents, vX acts upon
the body much like sarin does but more quickly. A miniscule
drop can be fatal. An oily liquid that evaporates slowly, it
lingers
on surfaces for days and can kill within minutes. Early symp-
toms include blurred vision, chest tightness, drooling and ex-
cessive sweating, nausea and small, pinpoint pupils.
• Anthrax — An infectious disease caused by a bacteria
found in soil, anthrax infects both domestic and wild animals

53. around the world, often fatally, but rarely humans naturally.
Anthrax is not contagious, but exposure to the miniscule spores,
less than a thousandth of an inch in size, can lead to serious
sickness or death. A person can become exposed by breath-
ing in anthrax, ingesting contaminated food or liquids or
through
an open wound. Anthrax can be treated with antibiotics, if di-
agnosed quickly enough.
• Smallpox — A contagious and sometimes fatal disease that
has killed tens of millions of civilians throughout history. Some
historians believe the British used smallpox-contaminated
blankets
as a weapon against Native Americans in colonial America.
Small-
pox was eradicated in the 20th century through a worldwide
vac-
cination program. But the smallpox virus still exists in
laboratory
samples and is considered a potential bioterrorism weapon
today.
Infection can come through face-to-face contact or by handling
contaminated objects such as clothing, or breathing contaminat-
ed air in closed spaces. The United States maintains a large sup-
ply of smallpox vaccine in the event of an outbreak.
• Pneumonic Plague — A relative of the bubonic plague
(“Black Death”) that wiped out a third to a half of Europe’s
population in the middle Ages, the pneumonic plague can be
transmitted from person to person. Symptoms of the poten-
tially fatal disease usually include fever, weakness and rapidly
developing pneumonia. The United States has antibiotics that
could be used to treat pneumonic plague. Like smallpox and
other disease agents, it is considered most likely to be used
as a weapon by terrorists or individuals rather than by a mili-
tary force.

54. — Reed Karaim
1 most of the information in this sidebar on chemical and
biological agents
comes from the Centers for Disease Control and Prevention
website. for more
complete lists and further details, see “Chemical weapons
Information,”
www.cdc.gov/nceh/demil/chemical_agent.htm, and “General
fact Sheets on
Specific Bioterrorism Agents,”
http://emergency.cdc.gov/bioterrorism/fact
sheets.asp.
from Anthrax to mustard Gas
Chemical and biological weapons have a variety of
characteristics.
Dec. 13, 2013 1059www.cqresearcher.com
But other analysts say the relative
military ineffectiveness of chemical
weapons argues against the idea they
are worse than other weapons. “Be-
cause they are hard to use in most
battlefield situations, chemical weapons
are usually less lethal than non-taboo
weapons like high explosives,” wrote
Stephen m. walt, a professor of inter-
national affairs at Harvard University
in Cambridge, mass. 10
And in a civil war such as the Syr-

55. ian conflict, where President Assad has
regularly targeted civilian neighbor-
hoods held by the opposition, walt
asked, “Does it really matter whether
Assad is killing his opponents using
500-pound bombs, mortar shells, clus-
ter munitions, machine guns, icepicks
or sarin gas? Dead is dead, no matter
how it is done.” 11
Rubin counters that chemical
weapons can cause particularly brutal
injuries, and that victims can suffer
permanently scarred lungs, nerve
damage and other lingering disabili-
ties. “The more relevant issue is not
how painful the death is, but what
happens to the walking wounded. You
have a much greater chance of re-
covering from a bullet or shrapnel
wound than you do recovering from
mustard gas or sarin,” Rubin says. “Once
the hostilities end, you can really suffer
the effects of this much more acutely
than the effects of a bullet wound,
often for the rest of your life.”
But Tierney believes drawing a line
around chemical weapons can have an
unintended negative consequence. “If you
say chemical weapons are unacceptable
in Syria, you’re implicitly saying that con-
ventional weapons are acceptable,” he
says. “You have to be careful about draw-
ing these lines because there’s a way in
which you legitimize war on the other

56. side of the line.”
making the kind of weapon used
the determining factor in one’s response
to a conflict, he says, misses a larger
point. “what I’d like to see is less focus
on the means by which leaders kill
and more on the ends: How many peo-
ple killed? focus more on the amount
of human suffering and the overall sit-
uation and less on the specific means.”
The University of British Columbia’s
Price, however, says ruling chemical
weapons out of bounds has limited
the potential for mass destruction in
war. when chemical weapons first came
on the scene, they were seen as po-
tential weapons of mass destruction,
he says. “People thought, ‘Oh my God,
you’re going to wipe out whole cities.’
And that’s why there were efforts to
curtail them. Chemical weapons have
never lived up to that, . . . in part be-
cause of the restraints we’ve imposed.”
Anything that gets the world to say
someone has gone too far when it
comes to making war should be con-
sidered a positive, he adds. “we ought
to be grateful that we have some of
these thresholds, at least, that galva-
nize humanitarian attention and re-
sponse around the world,” he says.

57. But for others, lumping chemical
and biological weapons together with
nuclear arms as “weapons of mass de-
struction,” as some U.S. policymakers
have done, overstates their capacity for
destruction. “I’ve always had trouble
with that trilogy,” says the University of
Arizona’s Guertner. “Nuclear weapons
are in a category all by themselves.
Neither chemical nor biological weapons
are going to cause mass casualties in
the sense that nuclear weapons are.”
Although chemical weapons are not
as destructive as nuclear weapons,
Rubin says that doesn’t mean they’re
not unusually cruel weapons.
“The real question is, do we say
chemical weapons should become nor-
mal in war? Ultimately, I would say
no. You risk opening a Pandora’s box
if you do,” he says. “You’re erasing a
line that was drawn almost 100 years
ago, and then you have to debate
about where you draw the new line.”
Are biological weapons a serious
threat to the United States?
A week after the Sept. 11, 2001, ter-
rorist attacks on the United States, letters

58. Photographs of Iraqi Kurds gassed by Iraqi President Saddam
Hussein are
displayed at a memorial in the Kurdish town of Halabja, in
northern Iraq.
By some estimates 50,000-60,000 Iranians and Kurds were
killed or wounded
in Iraqi gas attacks during the Iran-Iraq War in the 1980s, which
led in part
to the 1993 Chemical Weapons Convention.
A
F
P
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es
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li
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aa
di

59. 1060 CQ Researcher
containing anthrax spores were mailed
to offices of two …
LECTURES 19 & 20 BACK to the FUTURE
In the “history of the world according to salt ” (Lecture 17),
animals wore paths to salt licks; men followed; trails became
roads, and settlements grew beside them. When the human menu
shifted from salt-rich game to cereals (see Lecture 1), more salt
was needed to supplement the diet. Since underground deposits
were beyond reach, and the salt sprinkled over the surface was
insufficient, scarcity kept the mineral (Halite) precious. As
civilization spread, salt became one of the world’s principal
trading commodities. In these final lectures we will follow the
transition in hunter-gatherer societies about ~ 10,000 BC to
residential settlements in which Agriculture provided
sustenance. The chemical, biochemical and geochemical
processes that advanced this evolution will be brought out
resulting, eventually, in the GreenRevolution of the 20th
century in which water management, fertilizers, and pesticides
succeeded in alleviating the starvation of millions. The
“downsides” of this revolution will be discussed, e.g., nitrogen
loading and pollution. Historians also note that the introduction
of Agriculture led to the concepts of “labor” and “property”
which resulted, in turn, in the stratification of human societies
(serfdom, slavery) and warfare.
When did it all start?
James Ussher (1581 – 1656) was, in the Church of Ireland,
the Archbishop of Armagh between 1625 and 1656. He was a

60. prolific scholar and church leader, most famous for his
identification of the letters of Saint Ignatius of Antioch, and
for an amazing piece of scholarship in which he used the Julian
calendar to “back track” the chronology in the Bible to establish
the time and date of creation in Genesis as "the entrance of the
night preceding the 23rd day of October... the year before Christ
4004," that is, ~ 6 pm on October 22, 4004 BC.
Today the theory known as the Big Bang is a cosmological
model of the observable universe from the earliest known
periods through its subsequent large-scale evolution. The model
describes how the universe expanded from an initial state of
very high density and temperature, and offers a comprehensive
explanation for a broad range of observed phenomena, including
the abundance of light elements, cosmic microwave
backgroundradiation, the large-scale structure of the Universe,
and Hubble's law (the farther away galaxies are, the faster they
are moving away from Earth).
If the observed conditions are extrapolated backwards in time
using the known laws of physics, the prediction is that just
before a period of very high density there was a singularity.
See Lecture 13. Based on measurements of the expansion
using Type Ia supernovae and measurements of temperature
fluctuations in the cosmic microwave background radiation, the
time that has passed since that event, known as the "age of the
universe, " is 13.799 ± 0.021 billion years.As noted in Lecture
13, current knowledge is insufficient to determine if anything
existed prior to the singularity, the modern version of the
hypothetical question posed by Saint Augustine (354-430 AD)
in his Confessions, “ What was God doing before he created the
Universe? ”
Stellar nucleosynthesis, the process by which elements are
created within stars by combining

61. protons and neutrons together from the nuclei of lighter
elements, was discussed in Lecture 16. All of the atoms in the
universe began as hydrogen. Fusion inside stars transforms
hydrogen into helium, heat, and radiation. Heavier elements are
created in different types of stars as they die or explode.
The fusion limit is iron (Fe), atomic number 26. Synthesizing
heavier elements requires energy. The first pathway involves
neutron stars resulting from the collapsed “leftovers” of stars
with mass > 8 times the mass of the Sun. In a supernova
explosion, the collapsed core of a neutron star creates pressures
so great that electrons and protons are forced to merge creating
neutrons. In this way, elements up to and including lead (Pb,
atomic number 82) are synthesized. That still leaves
unexplained elements with atomic number > 82.
Last year, the collision of two neutron stars was observed,
something called a kilonovaexplosion, a rare event occurring
only once every 10,000 to 100,000 years.
Black holes of stellar mass are expected to form when very
massive neutron stars collapse at the end of their life cycle. The
explosion creates a gravitational wave, predicted in 1916 by
Einstein in his General Theory of Relativity (see Lecture 16),
and confirmed experimentally on September 14, 2015, when
LIGO (LIGO stands for “Laser Interferometer Gravitational-
wave Observatory’) sensed the predicted undulations in space-
time caused by gravitational waves generated by two black
holes colliding 1.3 billion light-years away.
In a kilonova explosion, neutrons are scattered in all directions,
and existing nuclei absorb neutrons. Neutrons in bombarded
nuclei spit out electrons creating protons. More protons means
higher atomic numbers and, voilà, we have the whole Periodic
Table of Elements and hence all of Chemistry !

62. What happened after the Big Bang?
According to our current understanding of cosmology, the
Universe was featureless and dark for a long stretch of its early
history. The first stars did not appear until perhaps 100 million
years after the Big Bang, and nearly a billion years passed
before galaxies proliferated across the cosmos. How did this
dramatic transition from darkness to light come about?
Cosmologists have devised models that show how the density
fluctuations left over from the Big Bang could have evolved
into the first stars.
The models indicate that the first stars were most likely quite
massive and luminous and that their formation was an epochal
event that fundamentally changed the Universe and its
subsequent evolution. These stars altered the dynamics of the
cosmos by heating and ionizing the surrounding gases. The
earliest stars also produced and dispersed the first heavy
elements, paving the way for the eventual formation of solar
systems like our own. And, the collapse of some of the first
stars may have seeded the growth of supermassive black holes
that formed in the hearts of galaxies and became the spectacular
power sources of quasars.Deductions about the early Universe
are based on analyzing the cosmic microwave background
radiation which was emitted about 400,000 years after the Big
Bang. The uniformity of this radiation indicates that matter was
distributed very smoothly at that time. Because there were no
large luminous objects to disturb the primordial soup, it must
have remained smooth and featureless for millions of years
afterward. As the cosmos expanded, the background radiation
redshifted to longer wavelengths and the universe grew
increasingly cold and dark. Astronomers have no observations

63. of this dark era. But, by a billion years after the Big Bang,
some bright galaxies and quasars had already appeared, so the
first stars must have formed sometime before.
Although the early universe was remarkably smooth, the
background radiation shows evidence of small-scale density
fluctuations, clumps in the primordial soup. The cosmological
models predict that these clumps would gradually evolve into
gravitationally bound structures. Smaller systems would form
first and then merge into larger agglomerations. The denser
regions would take the form of a network of filaments, and the
first star-forming systems, small protogalaxies, would coalesce
at the nodes of this network.
Similarly, the cosmological models predict that protogalaxies
would then merge to form galaxies, and the galaxies would
congregate into galaxy clusters. Although galaxy formation is
now mostly complete, galaxies are still assembling into clusters,
which are in turn are aggregating into a vast filamentary
network that stretches across the universe.
According to the cosmological models, the first small systems
capable of forming stars should have appeared between 100
million and 250 million years after the Big Bang. These
protogalaxies would have been 100,000 to one million times
more massive than the Sun and would have measured about 30
to 100 light-years across. These properties are somewhat similar
to those of the molecular gas clouds in which stars are currently
being formed in the Milky Way.
The first protogalaxies differed from molecular clouds in
fundamental ways. First, they would have consisted mostly
of dark matter, elementary particles that are believed to make
up about 90 % of the Universe’s mass. In present-day large
galaxies, dark matter is segregated from ordinary matter. Over
time, ordinary matter concentrates in the galaxy’s inner region,
whereas the dark matter remains scattered throughout an
enormous outer halo. In protogalaxies, the ordinary matter
would still have been mixed with the dark matter.

64. The second important difference is that the protogalaxies would
have contained no significant amounts of any elements besides
hydrogen and helium. The Big Bang produced hydrogen and
helium, but heavier elements were created later via stellar
nucleosynthesis, as described above.The formation and
evolution of the Solar System began ~ 4.5 billion years ago with
the gravitational collapse of a small part of a giant molecular
cloud. Most of the collapsing mass collected in the center,
forming the Sun, while the rest flattened into a protoplanetary
disk out of which the planets, moons, asteroids, and other small
bodies formed.
How do we know that the Earth formed ~ 4.5 billion years ago?
Whereas the above scenario is based on cosmological models
and important assumptions (in particular, the existence of dark
matter which, thus far, has not been confirmed experimentally),
on this question a more definite answer can be given.
In 1830, the Scottish geologist Charles Lyell, developing ideas
put forward by the Scottish natural philosopher James Hutton,
popularized the concept that the features of Earth were in
perpetual change, eroding and reforming continuously, and the
rate of this change was roughly constant.
In 1862, the physicist William Thomson (who later became Lord
Kelvin) at the University of Glasgow published calculations that
fixed the age of Earth at between 20 million and 400 million
years. He assumed that Earth had formed as a completely
molten object, and determined the amount of time it would take
for the near-surface to cool to its present temperature. His
calculations did not account for heat produced via radioactive
decay (a process then unknown to science) or convection inside

65. the Earth, which allows more heat to escape from the interior to
warm rocks near the surface.
Geologists had trouble accepting such a short age for Earth.
Biologists could accept that Earth might have a finite age, but
even 400 million years seemed much too short to be plausible.
Charles Darwin, who had studied Lyell's work, proposed his
theory ofevolution of organisms by natural selection, a process
whose combination of random heritable variation and
cumulative selection implies great expanses of time.
Geneticists have subsequently measured the rateofgenetic
divergence of species, and dated the last, universal ancestor of
all living organisms to have lived ~3.5-3.8 billion years ago.
Ernest Rutherford and Frederick Soddy, in their work on
radioactive materials at McGill University, concluded that
radioactivity was due to a spontaneous transmutation of atomic
elements. See Lecture 16. In radioactive decay, an element
breaks down into another, lighter element, releasing alpha, beta,
or gamma radiation in the process. They also determined that a
particular isotope of a radioactive element decays into another
element at a distinctive rate. This rate is given in terms of a
"half life", or the amount of time it takes for half the mass of
that radioactive material to break down into its "decay product".
Some radioactive materials have short half-lives; some have
long half-lives. Uranium and thorium have long half-lives, and
so persist in Earth's crust, but radioactive elements with short
half-lives have generally disappeared. This suggested to
Rutherford that it might be possible to measure the age of Earth
by determining the relative proportions of radioactive materials
in geological samples.
A radioactive element does not always decay into one
nonradioactive ("stable") element directly, but instead can
decay into other radioactive elements that have their own half-
lives (and so on) until they reach a stable element. Such
"decay series" (e.g., the uranium-radium and thorium series)
were known within a few years of the discovery of

66. radioactivity, and provided a basis for constructing techniques
of radiometric dating.
Typical radioactive end products are argon from potassium-40
and lead from uranium and thorium decay. If the rock becomes
molten, as happens in Earth's mantle, such nonradioactive end
products typically escape or are redistributed. Thus the age of
the oldest terrestrial rock gives a minimum for the age of Earth
assuming that a rock cannot have been in existence for longer
than Earth itself. According to radiometric dating and other
evidence, Earth formed ~4.5 billion years ago.
What has happened over the past 4.5 billion years?
As developed in Lectures 17 and 18, tectonic activity over
billions of years, coupled to physical and chemical weathering
and chemical erosion led to the landforms we see today.
Earth is the third planet from the Sun and the only astronomical
object known to harbor life. According to radiometric dating,
Earth formed over 4.5 billion years ago, and studies in genetics
have established that the last universal ancestor of all living
organisms could be dated 3.5-3.8 billion years ago. Subtraction
shows that less thana billion years separated the solidification
of the Earth’s crust from the evolution of life on Earth !
The chemistry of the inorganic compounds making up the
Earth’s crust was the subject of Lectures 1-4. The chemistry of
Carbon and the biochemistry of life was the subject of Lectures
5-8.
The history of agriculture is the story of humankind's
development and cultivation of processes for producing food,
feed, fiber, fuel, and other goods by the systematic raising
of plants and animals. Prior to the development of plant
cultivation, human beings were hunters and gatherers. The
knowledge and skill of learning to care for the soil and growth
of plants advanced the development of human society, allowing
clans and tribes to stay in one location generation after

67. generation. Archaeological evidence indicates that such
developments occurred ~10,000 or more years ago.
Because of agriculture, cities as well as trade relations between
different regions and groups of people developed, further
enabling the advancement of human societies and cultures.
Agriculture has been an important aspect of economics
throughout the centuries prior to and after the Industrial
Revolution. Sustainable development of world food supplies
impact the long-term survival of the species, so care must be
taken to ensure that agricultural methods remain in harmony
with the environment.
Agriculture is believed to have been developed at multiple times
in multiple locations, the earliest of which seems to have been
in Southwest Asia in an area referred to as the FertileCrescent.
Pinpointing the absolute beginnings of agriculture is
problematic because the transition away from hunter-gatherer
societies in some areas began many thousands of years before
the invention of writing. Nonetheless, archaeobotanists and
paleoethnobotanists have traced the selection and cultivation of
specific food plant characteristics, such as a semi-tough rachis
and larger seeds, to just after ~ 9,500 BC in the
early Holocene period in the Levant region of the Fertile
Crescent.
There is evidence for the earlier use of wild cereals.
Anthropological and archaeological evidence from sites across
Southwest Asia and North Africa indicate use of
wild grain (from the ~ 20,000 BC site of Ohalo II in Israel,
many Natufian sites in the Levant and from sites along
the Nile in the 10th millennium BC.).

68. There is even early evidence for planned cultivation and trait
selection: grains of rye with domestic traits have been recovered
from ~ 10,000 BC sites at Abu Hureyra in Syria, but this
appears to be a localized phenomenon resulting from cultivation
of stands of wild rye, rather than a definitive step towards
domestication. It isn't until after ~ 9,500 BC that the eight so-
called foundation crops of agriculture appear: first emmer and
einkorn wheat (see Lecture 1), then hulled barley, peas, lentils,
bitter vetch, chick peas, and flax. These eight crops occur more
or less simultaneously on Pre-Pottery Neolithic sites in the
Levant, although the consensus is that wheat was the first to be
sown and harvested on a significant scale.
By ~ 7000 BC, sowing and harvesting reached the Levant and
there, in the super fertile soil just north of the Persian
Gulf, Sumerian ingenuity systematized and scaled it up. By
~6000 BC, farming was entrenched on the banks of the Nile
River.
About this time, agriculture was developed independently in the
Far East, probably in China, with rice rather than wheat as the
primary crop. Maize was first domesticated, probably from
native teosinte, in the Americas around 3000-2700 BC, though
there is some archaeological evidence of a much earlier
development. The potato, the tomato, the pepper, squash,
several varieties of bean, and several other plants were also
developed in the New World, as was quite extensive terracing of
steep hillsides in much of AndeanSouth America.
Agriculture was also independently developed on the island
of New Guinea.
The reasons for the development of farming may have included
climate change, but possibly there were also social reasons
(such as accumulation of food surplus for competitive gift-
giving (as in the Pacific Northwest potlatch culture). Most

69. certainly, there was a gradual transition from hunter-gatherer to
agricultural economies after a lengthy period during which some
crops were deliberately planted and other foods were gathered
in the wild. Although localized climate change is the favored
explanation for the origins of agriculture in the Levant, the fact
that farming was “invented” at least three times elsewhere, and
possibly more, suggests that social reasons may have been
instrumental.
Full dependency on domestic crops and animals did not occur
until the Bronze Age (3000–1200 BC ) by which time wild
resources contributed a nutritionally insignificant component to
the usual diet. If the operative definition of agriculture
includes large scale intensive cultivation of land, mono-
cropping, organized irrigation, and use of a specialized labor
force, the title "inventors of agriculture" would fall to
the Sumerians, starting around ~ 5,500 BC.
Intensive farming allows a much greater population density than
can be supported by hunting and gathering, and allows for the
accumulation of excess product for off-season use, or to sell or
barter. The ability of farmers to feed large numbers of people
whose activities have nothing to do with material production
was the crucial factor in the rise of division oflabor, the sense
of property and standing armies.
Agriculture of the Sumerians supported a substantial territorial
expansion, together with much internecine conflict between
cities, making them the first empire builders. Not long after, the
Egyptians, powered by farming in the fertile Nile valley,
achieved a population density from which enough warriors
could be drawn for a territorial expansion, more than tripling
the Sumerian empire in area.
ANCIENT AGRICULTURE

70. SUMERIEN AGRICULTURE
In Sumer (the area that later became Babylonia and is now
southern Iraq, from around Baghdad to the Persian
Gulf), barley was the main crop, but wheat, flax, dates, apples,
plums, and grapes were grown as well. While Mesopotamia was
blessed with flooding from the Tigris and Euphrates rivers that
helped cultivate plant life, salt deposits under the soil, made it
hard to farm. The earliest known sheep and goats were
domesticated in Sumer and were in a much larger quantity than
cattle. Sheep were kept mainly for meat and milk, and butter
and cheese were made from the latter. Ur, a large town that
covered about 50 acres, had 10,000 animals kept in sheepfolds
and stables and 3,000 slaughtered every year. The city's
population of 6,000 included a labor force of 2,500 cultivating
3,000 acres of land. The labor force contained storehouse
recorders, work foremen, overseers, and harvest supervisors to
supplement laborers. Agricultural produce was given to the
Gala, priests of the Sumerian goddess Inanna, important people
in the community. Shown below is a Sumerian harvester’s
sickle made of baked clay, ~ 3000 BC, in the Field Museum.
The land was plowed by teams of oxen pulling light plows w/o
wheels and grain was harvested with sickles. Wagons had solid
wheels covered by leather tires kept in position by copper nails
and were drawn by oxen and the Syrian onager (now extinct).
Animals were harnessed by collars, yokes, and head stalls. They
were controlled by reins, and a ring through the nose or upper
lip and a strap under the jaw. As many as four animals could
pull a wagon at one time. Though some hypothesize that
domestication of the horse occurred as early as ~ 4000 BC in
the Ukraine, the horse was definitely in use by the Sumerians