The atmosphere is made up of the following gases, Nitrogen 78%, Oxygen 21%, Argon 1%, Carbon dioxide 0.03%, water - variable
C6.08 The composition of the atmosphere
The atmosphere is made up of the following gases, Nitrogen
78%, Oxygen 21%, Argon 1%, Carbon dioxide 0.03%, water - variable
C6.09 Earth's early atmosphere and volcanoes
The primary atmosphere of the Earth was hydrogen and helium.
These light gases were slowly lost. They were replaced by a secondary atmosphere produced by
the action of volcanoes.
C6.10 Composition of the Earth's early atmosphere
The Earth's secondary atmosphere was made up of some left over hydrogen, carbon dioxide,
water vapour, nitrogen, carbon
monoxide,
sulphur dioxide ammonia and methane.
Task C6.10 Match these formulae to secondary
atmosphere gases: CH4, SO2, CO2, H2,
NH3, CO, N2, H2O.
C6.11 Origin of the oceans
As the Earth cooled to below 100oC oceans were
formed when water vapour condensed and formed liquid water. Oceans are
reservoirs for carbon dioxide because they can store the gas when it dissolves
in them. The new oceans dissolved a great deal of the carbon dioxide
in the atmosphere. The oceans still play a part in keeping carbon dioxide
levels constant. If there is a lot of carbon dioxide in the air then
more can dissolve. If there is less carbon dioxide in the air then
some comes out of solution back into the air.
C6 12 The release of oxygen into the atmosphere
As the temperature of the Earth cooled simple green plants
evolved in the oceans to use the carbon dioxide in the environment.
These green plants steadily removed carbon dioxide and produced oxygen
by photosynthesis. Oxygen levels in the atmosphere slowly increased.
.jpg)
C6.13 The carbon cycle
The carbon cycle helps to keep the atmospheric composition
constant by
adding carbon dioxide to the atmosphere and also taking carbon dioxide
away from the atmosphere. Carbon dioxide is taken away from the atmosphere
or out of the cycle by photosynthesis, dissolving in water and by chemical
reactions, for example with rock. It is brought
into the atmosphere or into the cycle by respiration, combustion, volcanic
activity and decay.
C6.14 Formation of igneous rocks
Igneous rocks are formed when magma pushes up into the crust
and cools. It is made up of crystals It does not contain any
fossils. Any living thing falling into the molten rock, from which it is made
would be burnt and leave no trace. Igneous rock forms as magma cools slowly under the surface e.g.
Granite. Magma reaching the surface through a volcano cools quickly
e.g. basalt. See some igneous rock
C6.15 Crystal size and igneous rock
Igneous rocks which cool slowly have large crystals
e.g. granite but rock
forming quickly has smaller crystals e.g. balsalt.
C6.16 The formation of sedimentary rock
This rock is formed in shallow seas. After long periods of time sediment layers pile up and the
lower ones come under great pressure. This pressure pushes the water out
of the layers or sediments and salt crystallizes and sticks the particles
together to form sedimentary rocks. This process is called lithification.
Living things falling into the
sediments leave an impression as the rock forms (a fossil). Fossils show
that a rock was made from sediments.
C6.17 Dating sedimentary rock
Sedimentary rock forms in layers. New sediments
are layered on top of old ones so the age of sedimentary rock increases
with depth. Species become extinct and new species take their place so
fossils of different species are of known age can be used to date the rock.
C6.18 Formation of metamorphic rock
Metamorphic rocks are formed by the action of heat and pressure
over long periods of time on rocks that are already formed. Earth movements push all types of rock underground,
here they are compressed and heated and the mineral structure and texture
may change. For example marble is formed from limestone. Rock cycle presentation (needs
Powerpoint)
C6.19 The composition of metamorphic rock
Metamorphic rock has the same chemicals in it as the rock that it was made
from. Limestone is made of calcium carbonate. Marble is a
metamorphic rock made from limestone. It is also made of calcium
carbonate. Mudstone in a sedimentary rock which turns into the metamorphic
rock called slate. Both mudstone and slate contain the same clay like
minerals. See some metamorphic rocks