1. Teacher: R. I. Nikolaeva.
Form 11 ‘B’.
The Unit №2.14.
Student's Book ‘Starlight’ 11.
(Authors: Virginia Evans, Ksenia Baranova)
The Theme of the unit:
‘Is ground solid enough to stand on?‘
The aim of the unit:
Curricular cut. Form of work:
Work in groups.
1) Collecting information about Earth's plates
2) Making Projects on the topic.
3) Presentation Projects to the class.
The material used: Internet, technical literature, Student's Book.

2. Inner core
The inner core of the Earth, its innermost part, is a primarily solid ball with a
radius of about 1,220 km (760 mi), according to seismological studies. This
is about 70% of the Moon's radius.) It is believed to consist primarily of an
iron-nickel alloy, and to be approximately the same temperature as the
surface of the Sun: approximately 5430 C.

3. Discovery
The Earth was discovered to have a solid inner core distinct from its liquid
outer core in 1936, by the seismologist Inge Lehmann who deduced its
presence from observations of earthquake-generated seismic waves that
reflect off the boundary of the inner core and can be detected by sensitive
seismographs on the Earth's surface. This boundary is known as the Bullen
discontinuity, or sometimes as the Lehmann discontinuity. A few years
later, in 1940, it was hypothesized that this inner core was made of solid
iron; its rigidity was confirmed in 1971.

4. The outer core was determined to be liquid from observations showing that
compressional waves pass through it, but elastic shear waves do not - or do so
only very weakly. The solidity of the inner core had been difficult to establish
because the elastic shear waves that are expected to pass through a solid mass
are very weak and difficult for seismographs on the Earth's surface to detect,
since they become so attenuated on their way from the inner core to the surface
by their passage through the liquid outer core. Dziewonski and Gilbert
established that measurements of normal modes of vibration of Earth caused by
large earthquakes were consistent with a liquid outer core. Recent claims that
shear waves have been detected passing through the inner core were initially
controversial, but are now gaining acceptance

5. Composition
Based on the relative prevalence of various chemical elements in our solar system,
the theory of planetary formation, and constraints imposed or implied by the
chemistry of the rest of the Earth's volume, the inner core is believed to consist
primarily of a nickel-iron alloy known as NiFei 'Ni' for nickel, and 'Fe* for ferrum
orion. The core also contains enough gold, platinum and other siderophile
elements, which would cover the entire Earth with a coating 0.45 m deep. Core's
temperature is about 5,700 К (5,430 °C; 9,800 °F). The pressure in the Earth's
inner core is slightly higher than it is at the boundary between the outer and inner
cores: it ranges from about 330 to 360 gigapascals.

6. Temperature and pressure
The temperature of the inner core can be
estimated by considering both the
theoretical and the experimentally
demonstrated constraints on the melting
temperature of impure iron at the pressure
which iron is under at the boundary of the
inner core (about 330 GPa). These
considerations suggest that its
temperature is about 5,700 K.

7. The crust
In geology, the crust is the outermost solid shell of a rocky planet or natural
satellite, which is chemically distinct from the underlying mantle. The crusts of
Earth, the Moon, Mercury, Venus, Mars, Io, and other planetary bodies have
been generated largely by igneous processes, and these crusts are richer in
incompatible elements than their respective mantles.

8. Earth's crust and mantle
The crust of the Earth is composed of a great variety of igneous, metamorphic, and
sedimentary rocks. The crust is underlain by the mantle. The upper part of the
mantle is composed mostly of peridotite, a rock denser than rocks common in the
overlying crust.
The crust occupies less than 1% of Earth's volume.[l] The oceanic crust of the
sheet is different from its continental crust. The oceanic crust is 5 km (3 mi) to 10
km (6 mi) thick[2] and is composed primarily of basalt, diabase, and gabbro. The
continental crust is typically from 30 km (20 mi) to 50 km (30 mi) thick and is
mostly composed of slightly less dense rocks than those of the oceanic crust.
Some of these less dense rocks, such as granite, are common in the continental
crust but rare to absent in the oceanic crust. Both the continental and oceanic crust
"float" on the mantle. Because the continental crust is thicker, it extends both
above and below the oceanic crust. The slightly lighter density of felsic continental
rock compared to basaltic ocean rock contributes to the higher relative elevation of
the top of the continental crust. Because the top of the continental crust is above
that of the oceanic, water runs off the continents and collects above the oceanic
crust. The continental crust and the oceanic crust arc sometimes called sial and
sima respectively. Because of the change in velocity of seismic waves it is believed
that on continents at a certain depth sial becomes close in its physical properties to
sima, and the dividing line is called the Conrad discontinuity.

10. Composition
The continental crust has an average composition similar to that of andcsite.
Continental crust is enriched in incompatible elements compared to the basaltic
ocean crust and much enriched compared to the underlying mantle. Although the
continental crust comprises only about 0.6 weight percent of the silicate on
Earth, it contains 20% to 70% of the incompatible elements.

12. Lithosphere is the hard shell of the Earth, which includes the crust and part of
the upper mantle. Lithosphere thickness on land generally varies from 35-40 km
(in the plains) to 70 km (in mountainous areas). There's even more crustal
thickness under the ancient mountains: for example, under the Himalayas its
power reaches 90 km. The earth's crust under the oceans - is also the
lithosphere. Here she is fine - an average of about 7-10 km, and in some areas
of the Pacific Ocean - to 5 km.
The thickness of the crust can be determined by the propagation velocity of
seismic waves. The latter also give some information about the properties of the
mantle beneath the crust and a member of the lithosphere. Lithosphere, as well
as hydrosphere and atmosphere was formed primarily as a result of the release
of substances from the upper mantle of the young Earth. Its formation is still
going on, mainly on the ocean floor.
Most of the lithosphere constitutes crystalline substances, which were formed
during the cooling of magma - molten material in the Earth's depths. Hot
solutions were formed during the cooling of magma too. They were cooled and
recovered substances contained, passing through the cracks in the earth's crust.
Since some of the minerals and the temperature change of pressure decay on
the surface are converted into new compounds.

13. Lithosphere is exposed to air and water layers of the Earth (atmosphere and
hydrosphere), resulting in weathering processes. Physical weathering is a
mechanical process, in which rock is crushed to a smaller particle size, without
changing the chemical composition. Chemical weathering results in the formation of
new substances. Biosphere, as well as land topography and climate, affects the rate
of weathering, water composition and other factors.
Unconsolidated continental
deposits, the power of which is
ranging from 10-20 cm on the
steep slopes of up to tens of
meters on the plains and
hundreds of meters in the valleys,
were formed by weathering. Soils
, which play an important role in
the interaction of living organisms
with the crust, were formed on
these deposits.

14. An atmosphere is a layer of gases
surrounding a planet that is held in
place by the gravity. An atmosphere
is more likely to be retained if the
gravity is high and the atmosphere's
temperature is low. Earth's
atmosphere, which contains oxygen
used by most organisms for
respiration and carbon dioxide used
by plants, and bacteria for
photosynthesis, also protects living
organisms from genetic damage by
solar ultraviolet radiation. Its current
composition is the product of billions
of years of biochemical modification
of the paleoatmosphere by living
organisms.

16. The atmosphere of the Earth may be divided into several distinct layers. The
troposphere is where all weather takes place; it is the region of rising and falling
packets of air. Above the troposphere is the stratosphere, where air flow is
mostly horizontal. The thin ozone layer in the upper stratosphere has a high
concentration of ozone, a particularly reactive form of oxygen. This layer is
primarily responsible for absorbing the ultraviolet radiation from the Sun.
Above the stratosphere is the mesosphere and above that is the ionosphere (or
thermosphere), where many atoms are ionized (they have gained or lost
electrons so they have a net electrical charge). The ionosphere is very thin, but
it is where aurora take place, and is also responsible for absorbing the most
energetic photons from the Sun, and for reflecting radio waves, thereby making
long-distance radio communication possible.
The Earth's atmosphere is about 480 km thick, but most of the atmosphere
(about 80%) is within 16 km of the surface of the Earth. There is no exact place
where the atmosphere ends; it just gets thinner and thinner, until it merges with
outer space.

18. The hydrosphere - the water
cover of Earth including oceans,
the seas, the rivers, lakes,
underground waters and
glaciers, a snow cover, and also
water vapor in the atmosphere.
Earth hydrosphere for 94% is
presented by salty waters of
oceans and the seas, more than
75% of all fresh water are
preserved in polar caps of the
Arctic and Antarctica.

19. Water on Earth is present at all three aggregate states, however its greatest
volume is the share of a liquid phase which is very significant for formation of
other features of a planet. All natural water complex functions as a unit, being
in a condition of continuous movement, development and updating. The
surface of the World Ocean occupying about 71% for a terrestrial surface, is
located between the atmosphere and a lithosphere. Earth diameter, i.e. its
equatorial diameter, makes 12 760 km, and the average depth of the ocean in
its modern bed - 3,7 km. Therefore, thickness of a sheet of water in a liquid
state averages only 0,03% of terrestrial diameter. In effect, it is the thinnest
water film on Earth surface, but, as the ozone protective layer, playing an
extremely important role in biospheric svstem.

20. Without water there couldn't be a person, an animal and flora as the majority of
plants and animals consists generally of water. Besides, temperatures are
necessary for life in the range from 0 to 100 °C that corresponds to temperature
limits of a liquid phase of water. For many living beings water serves as habitat.
Thus, the main feature of the hydrosphere is abundance of life in it.

21. The hydrosphere role in maintenance of rather invariable climate on a planet as
she, on the one hand, acts as heat accumulator is great, providing constancy of
average planetary temperature of the atmosphere, and with another -at the
expense of a phytoplankton produces nearly a half of all oxygen of the
atmosphere.
The water environment is used for fishing of fish and other seafood, collecting
plants, production of underwater deposits of ore (manganese, nickel, cobalt) and
oil, transportation of goods and passengers. In production and economic activity
of people applies water to cleaning, washing, cooling of the equipment and
materials, watering of plants, hydrotransportation, ensuring specific processes,
for example electric power developments, etc.

22. The important circumstance inherent
in the water environment, that
infectious diseases (about 80% of all
diseases) are generally transmitted
through it is. Simplicity of process of
flooding in comparison with other
types of burial, inaccessibility of
depths to the person and seeming
isolation of water led to that the
mankind actively uses the water
environment for dumping of production
wastes and consumption. Intensive
anthropogenous pollution of the
hydrosphere conducts to serious
changes of its geophysical
parameters, ruins water ecosystems
and it potentially danserous to the
person.

23. Ecological threat to the
hydrosphere set the task of
acceptance of urgent measures of
rescue of habitat of mankind for the
international community. Their
feature is that any state separately
even by means of strict measures
isn't capable to cope with
ecological threat. Therefore the
international cooperation in this
area, acceptance of the optimum
ecological strategy including the
concept and the program of joint
actions of all countries is
necessary.