Earth structure and atmosphere

What you need to know

Reflections and Exam tips

Earth structure and atmosphere

The Earth consists of a core, the mantle and the crust. It is surrounded by the atmosphere.

The Earth’s crust and the upper part of the mantle are cracked into a number of large pieces (tectonic plates).

Diagram

Convection currents in the Earth’s mantle are driven by heat released by natural radioactive processes. The convection currents cause the plates to move at relative speeds of a few centimetres per year.

The movements can be sudden and disastrous. Earthquakes and volcanic eruptions occur at the boundaries between tectonic plates.

Continental drift

Alfred Wegener proposed that 300 million years ago there was only one continent, the ‘super-continent’ he named pangea. The ‘super-continent’ then broke into several pieces that drifted apart over time due to convection currents within the Earth's mantle.

Theory was rejected because:

1. Wegener was not a qualified geologist
2. Wegener's data was often inaccurate
3. Wegener could not provide an adequate explanation for continental drift.

Evidence

1. Identical fossils of plants and animals found on both sides of the Atlantic
2. Coastlines of South America and South Africa fit together like a jigsaw
3. Rocks with matching layers found on different continents
4. Tropical plant fossils found in the Artic. These could have never existed at that place on Earth due to the cold.

Atmosphere

For 200 million years, the proportions of different gases in the atmosphere have been much the same as they are today:

1. 78% nitrogen
2. 21% oxygen
3. 1% small proportions of various other gases, including carbon dioxide, water vapour and noble gases.

There are several theories about how the atmosphere was formed.

One theory suggests that during this period the Earth’s atmosphere was mainly carbon dioxide with little or no oxygen gas (similar to atmospheres of Mars and Venus today). The atmosphere may also have contained water vapour and small proportions of methane and ammonia.

During the first billion years of the Earth’s existence there was intense volcanic activity. The volcanic activity released the gases that formed the early atmosphere and water vapour that condensed to form the oceans.

Life on Earth

There are several theories as to how life was formed billions of years ago. Photosynthesing plants produced the oxygen that is now in the atmosphere.

The methane and ammonia burnt in the oxygen to produce more water, carbon dioxide and nitrogen.

Most of the carbon from the carbon dioxide in the air gradually became locked up in sedimentary rocks as carbonates and fossil fuels.

The oceans also acted as reservoir for carbon dioxide however increased amounts of carbon dioxide absorbed by the oceans has an impact on the marine environment due to an increase in acidity.

Nowadays, the burning of fossil fuels releases carbon dioxide which increases the level of carbon dioxide in the atmosphere.

Gases in air

Air is a mixture of gases with different boiling points. Air can be separated using fractional distillation to provide a source of raw materials used in a variety of industrial processes.

Know the three main parts of the Earth

Describe the impact of heat in the Earth

Explain why earthquakes and volcanoes occur

Compare today’s atmosphere with what it was billions of years ago

Explain what has happened on Earth to contribute to changes in the atmosphere

Describe theories that describe how life began