Download Changes in the Earth and its Atmosphere

Changes in the Earth
Continental drift and processes at
plate boundaries
What do I need to know?
• Recall the composition of the Earth and
movement of tectonic plates
• Describe how Wegener’s theory of continental
drift was not generally accepted for many
years
• Explain how movement of the plates can give
rise to earthquakes and volcanoes.
The structure of the Earth
• Label the following diagram
The structure of the Earth
• The Earth consists of a core, mantle and crust
and is surrounded by the atmosphere
• The Earth’s crust and the upper part of the
mantle are cracked into a number of large
pieces we call TECTONIC PLATES
Tectonic plates
Evidence for tectonic plate movement.
Copy and complete
• We call movement of the tectonic plates __________ drift.
• A scientist called __________ proposed this theory.
• Convection currents within the Earth’s ______ driven by heat
released by natural radioactive processes cause the plates to
_______.
• The plates move at relative speeds of a few __________ a
year.
[WEGENER, MANTLE, MOVE, CONTINENTAL, CENTIMETRES]
Wegener’s theory of continental drift
Write a short paragraph to explain why Wegener’s
theory of continental drift was not generally accepted
for many years:
------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
Considering the evidence
• Strong evidence for continental drift is found
by comparing rocks and fossils from different
continents and comparing these with animals
alive today.
• We can even test DNA to find out whether
certain species are related.
Earthquakes and volcanoes
Movements of the plates can be sudden and disastrous.
Earthquakes and volcanic eruptions occur at the boundaries
between tectonic plates when plates move and collide.
Predicting earthquakes and eruptions
Making predictions could save 1000’s of lives.
However, this is hard to do because scientists do
not know (with any certainty):
• what happens under the crust
• where the forces / pressure are building up
• the size of the forces
• when the forces reach their limit
Mid-ocean spreading ridge
• Using the internet find a diagram of a midocean ridge and draw it here…
Mid-ocean spreading ridges
Copy and complete
• These occur when two plates are moving _______.
• New ______ _______is created at the ridge because
as the plates move apart _______ rises to fill the gap.
• This _______ forming new rock.
• There is more ________ on rock further away from the
ridge because it is _______.
[MAGMA, COOLS, SEDIMENT, OCEAN FLOOR, APART,
OLDER]
Supporting life on Earth
The relationship between life and the
atmosphere
What do I need to know?
• Recall the current composition of gases in the
Earth’s atmosphere
• Describe how the atmosphere has evolved
and its relationship with the start of life on
Earth
• Explain some of the theories on the origins of
life.
The atmosphere today
• For 200 million years, the proportion of
different gases in the atmosphere have been
much the same as they are today.
Current proportions of gases
Oxygen 21 %
Nitrogen 78 %
Carbon dioxide 0.03 %
Other 0.9 %
Origins of the atmosphere
During the first billion years of the Earth’s
existence there was intense volcanic activity
This activity released the gas that formed the
early atmosphere and water vapour that
condensed to form the oceans.
http://www.youtube.com/watch?v=BvrzMBavDg
The nature of the atmosphere
• The atmosphere and the ocean are similar in
many ways. Their origins were in the same
volcanic eruptions that created the oceans
and they have many fluid features in
common.
• http://www.youtube.com/watch?v=1YAOT92
wuD8
The evolution of the atmosphere
• There are many theories about how the
atmosphere was formed.
• One of these suggests that during the first billion
years the atmosphere was mainly CO2 with little
or no O2 (like Mars and Venus). There was
probably also methane and ammonia.
• What process could have created the oxygen?
How did life begin?
There are many theories as to how life was
formed about 3.5 billion years ago. These
include:
• the interaction between hydrocarbons,
ammonia and lightning
• life arriving during meteor impacts; or
• formation of proteins in ice
• formation of carbon rich compounds at deep
sea vents.
Miller – Urey experiment
• This experiment carried out in the 1950s
demonstrated the potential to create the
building blocks of life in the laboratory.
• This is a contentious theory and just one of
many possibilities including deep sea vents,
meteors, comets and glaciers.
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