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 mid-ocean ridge and draw it here…

Mid-ocean spreading ridgesCopy 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=BvrzM-BavDg

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=1YAOT92wuD8

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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