Origin of atmosphere

1. Origin of Atmosphere

2. • Earth is believed to have formed about 5
billion years ago.
• In the first 500 million years, a dense
atmosphere emerged from the vapor and
gases that were expelled during degassing of
the planet’s interior.
– During the cooling of the earth, gases and water
vapour were released from the interior solid
earth. This started the evolution of the present
atmosphere. This process is called degassing.

3. • These gases may have consisted of hydrogen
(H2), water vapor, methane (CH4) , and carbon
oxides.
• Prior to 3.5 billion years ago the atmosphere
probably consisted of carbon dioxide (CO2),
carbon monoxide (CO), water (H2O), nitrogen
(N2), and hydrogen.
• The hydrosphere was formed 4 billion years
ago from the condensation of water vapor,
resulting in oceans of water in which
sedimentation occurred.

4. • The most important feature of the ancient
environment was the absence of free oxygen.
• Evidence of such an anaerobic reducing
atmosphere is hidden in early rock formations
that contain many elements, such as iron and
uranium, in their reduced states.
• Elements in this state are not found in the
rocks of mid-Precambrian and younger ages,
less than 3 billion years old.

5. • One billion years ago, early aquatic organisms called
blue-green algae began using energy from the Sun to
split molecules of H2O and CO2 and recombine them
into organic compounds and molecular oxygen (O2).
• This solar energy conversion process is known
as photosynthesis. Some of the photosynthetically
created oxygen combined with organic carbon to
recreate CO2 molecules.
• The remaining oxygen accumulated in the atmosphere,
touching off a massive ecological disaster with respect
to early existing anaerobic organisms.
• As oxygen in the atmosphere increased, CO2
decreased.

6. • High in the atmosphere, some oxygen (O2)
molecules absorbed energy from the Sun’s
ultraviolet (UV) rays and split to form single
oxygen atoms.
• These atoms combining with remaining
oxygen (O2) to form ozone (O3) molecules,
which are very effective at absorbing UV rays.
• The thin layer of ozone that surrounds Earth
acts as a shield, protecting the planet from
irradiation by UV light.

7. • The amount of ozone required to shield Earth
from biologically lethal UV radiation, wavelengths
from 200 to 300 nanometers (nm), is believed to
have been in existence 600 million years ago
• . At this time, the oxygen level was
approximately 10% of its present atmospheric
concentration.
• Prior to this period, life was restricted to the
ocean.
• The presence of ozone enabled organisms to
develop and live on the land.
• Ozone played a significant role in the evolution
of life on Earth and allows life as we presently
know it to exist.

8. 3 Phases of Atmosphere Formation
• Just formed Earth: Like Earth, the hydrogen
(H2) and helium (He) was very warm.
• These molecules of gas moved so fast they
escaped Earth’s gravity and eventually all
drifted off into space.

9. • Earth’s original atmosphere was probably just
hydrogen and helium because these were the main
gases in the dusty, gassy disk around the Sun from
which the planets formed.
• The Earth and its atmosphere were very
hot. Molecules of hydrogen and helium move really
fast, especially when warm.
• Actually, they moved so fast they eventually all
escaped Earth’s gravity and drifted off into space.

11. • Young Earth: Volcanoes released gases H2O
(water) as steam, carbon dioxide (CO2), and
ammonia (NH3).
• Carbon dioxide dissolved in seawater. Simple
bacteria thrived on sunlight and CO2. By-
product is oxygen (O2).

12. • Earth’s “second atmosphere” came from
Earth itself. There were lots of volcanoes,
many more than today because Earth’s crust
was still forming. The volcanoes released
– steam (H2O, with two hydrogen atoms and one
oxygen atom),
– carbon dioxide (CO2, with one carbon atoms and
two oxygen atoms),
– ammonia (NH3, with one nitrogen atom and
three hydrogen atoms).

14. • Current Earth: Plants and animals thrive in
balance.
• Plants take in carbon dioxide (CO2) and give
off oxygen (O2).
• Animals take in oxygen (O2) and give off CO2.
Burning stuff also gives off CO2.

15. • Much of the CO2 dissolved into the oceans.
Eventually, a simple form of bacteria
developed that could live on energy from the Sun
and carbon dioxide in the water, producing
oxygen as a waste product.
• Thus, oxygen began to build up in the
atmosphere, while the carbon dioxide levels
continued to drop.
• Meanwhile, the ammonia molecules in the
atmosphere were broken apart by sunlight,
leaving nitrogen and hydrogen.
• The hydrogen, being the lightest element, rose
to the top of the atmosphere and much of it
eventually drifted off into space.

17. • Now we have Earth’s “third atmosphere,” the
one we all know and love—an atmosphere
containing enough oxygen for animals,
including ourselves, to evolve.

18. Formation of Hydrosphere
• The hydrosphere formed approximately 4.5
billion years ago around the same time as the
atmosphere.
• When the planet formed, there were high
levels of volcanic activity, which expelled a
huge amount of water vapor into the air.
• Additionally, some minerals within the deeper
layers of earth contained water.

19. • As Earth cooled, the water vapor in the
atmosphere condensed and fell as rain.
• These cooler conditions meant that when water
reached the surface, it would not evaporate
instantly and could accumulate.
• These cooler conditions also meant that water
released by minerals in the crust could
accumulate on the surface as well.
• This marked the formation of the early
hydrosphere.
• Over time, water began to collect in large basins
forming oceans and seas.

20. CONCEPT OF MINERALS AND ROCKS
• Rocks and the minerals are known to be the
building blocks of our active planet.
• They are the reason how the landscapes are
formed and these provide all the necessary
valuable resources needed within our
environment.

21. What are Rocks?
• A Rock is an inorganic, solid and natural
substance without any specific atomic structure
or chemical composition.
• It is simple to remember that rocks are made up
of two or more minerals.
• Examples of rocks involve limestone, granite,
marble, slate and sandstone.
• Each of these rocks consists of different minerals
that can be mixed up with the rock through
different geologic processes.

22. • Let’s consider granite. It mostly consists of
three minerals namely: quartz, mica and
feldspar.
• All these minerals exist in nature but mixed up
with the rock.
• Sometimes you see big chunks of one of these
minerals in granite, but when you take that
stone as a whole, you have to call it rock.

24. What are Minerals?
• A mineral is defined as a natural, inorganic solid
substance which has a crystalline structure with a
particular chemical composition.
• A mineral is said to possess different chemical
composition which defines it crystalline shape
and form.
• Whereas, the rock which is said to be comprised
of several minerals, is generally classified based
upon the process of its formation.

26. Differences between Rocks and
Minerals

27. Types of Rocks
• There are three types of rocks:
• Igneous Rocks
• Sedimentary Rocks
• Metamorphic Rocks

28. Formation of Igneous Rocks
• Molten materials are found below the earth’s
crust and are normally subjected to extreme
pressure and temperatures – up to 1200°
Celsius.
• Because of the high temperatures and
pressure changes, the molten materials
sometimes shoot up to the surface in the form
of volcanic eruption and they cool down to
form volcanic or extrusive igneous rocks.

29. • Alternatively, some of the molten materials
may cool underneath the earth’s surface very
slowly to form plutonic or intrusive igneous
rocks.
• It is because of the extreme heat levels and
changes in pressure that igneous rocks do not
contain organic matter or fossils.
• The molten minerals interlock and crystallize
as the melt cools and forms solid materials.

30. • In the long-run, the melt forms a cool hard
rock made up of crystals with no open spaces
and don’t exhibit any desirable grain
alignment.
• The rocks may be made up entirely of one
mineral or various minerals, and their sizes are
determined by the cooling process.
• Rapid cooling results in smaller crystals while
slow cooling results in large crystals.

31. Types of Igneous Rocks
• Igneous rocks are of two types,
• intrusive (plutonic rocks) and extrusive
(volcanic rocks).

32. 1. Intrusive Igneous Rocks
• Intrusive igneous rocks are formed when the
magma cools off slowly under the earth’s crust
and hardens into rocks.
• Gabbro and granite are examples of intrusive
igneous rocks.
• Intrusive rocks are very hard in nature and are
often coarse-grained.

33. 2. Extrusive Igneous Rocks
• Extrusive igneous rocks are formed when
molten magma spill over to the surface as a
result of a volcanic eruption.
• The magma on the surface (lava) cools faster
on the surface to form igneous rocks that are
fine-grained.
• Examples of such kind of rocks include
pumice, basalt, or obsidian.

34. Examples of Igneous Rocks
• There are more than 700 known types of
igneous rocks and most of them are formed
under the earth’s crust since volcanic events
are not all that frequent.
• On this basis, we are going to look at the
commonly identified types of igneous rocks,
both intrusive and extrusive. They include:

35. 1. Granite
• Granites are the light-colored and coarse-grained
igneous rocks.
• They are intrusive rocks and they contain three
major minerals including feldspar, mica and
quartz.
• They appear pinkish, gray or tan depending on
the grain sizes and concentrations and grain sizes
of the three minerals.
• Granites are often used in construction activities
because of its strength and presence in great
quantities.

36. 2. Gabbro
• Gabbros are the dark-colored and coarse-
grained igneous rocks.
• They are intrusive rocks and they are made up
of mineral elements including pyroxene,
feldspar, and sometimes olivine.
• They appear grey in color with minute dark
spots all over them.

37. 3. Basalt
• Basalts are the dense dark-grey colored and
fine-grained igneous rocks.
• They are extrusive and are chiefly composed
of plagioclase and pyroxene.
• They are the commonest type of solidified
lava.
• Basalts are also frequently used in building
and construction.

38. 4. Diorite
• Diorites are the coarse-grained igneous rocks
just like the Gabbros and Granite.
• They are intrusive and contain a mixture of
minerals including hornblende, pyroxene,
feldspar and sometimes quartz.
• They appear light-colored with some dark
spots.

39. 5. Andesite
• Andesites are light grey-colored and fine-
grained igneous rocks.
• They are extrusive rocks which are mainly
made up of plagioclase minerals mixed up
with biotite, pyroxene, and hornblende.

40. Formation of Metamorphic rocks
• Metamorphic rocks are the rocks formed from
other rocks.
• They are sedimentary or igneous rocks that have
undergone changes as a result of extreme
pressure and heat.
• The name defines their formation whereby
‘meta’ means change and ‘morph’ means ‘form.’
• Hence, metamorphic rocks are those whose
forms have been changed through a geological
process such as large tectonic movements and
magma intrusions.

41. • Large tectonic movements and magma intrusions
create earth movements and subsequently cause
the pre-existing rocks to move and shift.
• In turn, the movements subject other rocks
buried deep below the earth’s surface to extreme
pressure and heat which contributes to changes
and assemblage of the rocks texture, mineralogy,
and chemical composition.

42. • The changes typically modify the rock’s crystal
type and sizes and may also subject the rocks
to further radical changes.
• Metamorphic processes come about at heats
between 150° and 795° Celsius with the
capability of producing high energy that can
break and reform the chemical compositions
of the rocks.
• Pressure from the overlying rocks also
increases the process of transformation.

43. • The heat from magma and friction along fault
lines is the major contributor of the heat that
brings about the rock changes.
• Even though the rocks do not actually melt,
some mineral groupings redistribute the
elements within the original minerals to form
new compositions of minerals that are more
stable at the new temperatures and pressures.

44. • The intense temperature gradient between
the country rocks and the surrounding molten
magma is the driving factor for the changes in
texture and chemical composition.
• As a result, the original rocks are
transformed into metamorphic rocks.
• Metamorphic rocks formed from direct
magma heating and intrusions are termed as
thermal or contact metamorphic rocks.

45. • Those formed as a result of widely distributed
pressure and temperature changes induced by
tectonic movements are known as regional
metamorphic rocks.

46. Types of Metamorphic Rocks
• There are two main types of metamorphic
rocks.
• These are Foliated metamorphic rocks and
Non-foliated metamorphic rocks.

47. 1. Foliated Metamorphic Rocks
• Foliated metamorphic rocks are formed from
direct exposure to pressure and heat.
• They are the most vital and largest groupings
of metamorphic rocks.
• Foliated metamorphic rocks have four
distinguishable types of aligned textures and
they normally have a banded or layered
appearance.

48. • Examples include slate, gneiss, phyllite, and
schist.
• Non-foliated are formed as a result of
tectonic movements or direct pressure which
makes their formation highly dependent on
their pre-existing conditions.

49. 2. Non-foliated Metamorphic Rocks
• Non-foliated metamorphic rocks do not have a
banded or layered appearance.
• The extensively known example of non-
foliated metamorphic rock is a marble.
• Other examples include quartzite, hornfels,
and novaculite.

50. Examples of Metamorphic Rocks
• 1. Hornfels
• Hornfels is a fine-grained metamorphic rock
formed by the action of heat on clay rocks,
known as contact metamorphism.
• It has a non-foliated metamorphic rock that
has no specific composition.
• Hornfels are heated when near a heat source
such as a sill, dike, or magma chamber.

51. 2. Amphibolite
• Amphibolite is non-foliated metamorphic rock
that is composed chiefly of plagioclase and
amphibole (hornblende), frequently with very
little quartz.
• Amphibolite forms under conditions of
directed pressure and high viscosity through
the process of recrystallization.

52. 3. Gneiss
• Gneiss is a foliated metamorphic rock made
up of granular mineral grains.
• It contains a lot of feldspar minerals and
bands of quartz and sometimes mica.
• It normally has a banded appearance and is
sort of laminated.
• It appears similar to granite.

53. 4. Novaculite
• Novaculite is a hard, fine-grained, dense,
siliceous rock.
• It is non-foliated metamorphic rocks known to
break with a conchoidal fracture.
• It forms in marine environments from
sediment deposits where organisms like
diatoms plentiful in water – the single-celled
algae that secret hard shells made up of
silicon dioxide.

54. 5. Marble
• Marble is among the non-foliated
metamorphic rocks produced from the
metamorphism of dolostone or limestone.
• It takes high polish and is often used for
sculpture and as building material.
• Marble is mainly composed of calcium
carbonate.