Chemistry-Our Changing Planet

Structure of the Earth

The Earth is made of layers called the core, mantle and crust with the atmosphere around the outside

• The Earth's limited resources come from its crust, the oceans and the atmosphere
• Ouside to Inside:
• Atmosphere
• Crust
• Mantle
• Outer core
• Inner core

The crust is a solid, it is a very thin layer that varies in thickness between about 5km and 70km.

The mantle is about 3000km thick. It goes almost halfway to the centre of the Earth. The mantle is almost entirely solid but parts of it can flow very slowly.

The core is about half the diameter of the Earth. It has a liquid outer part anda solid inner part

The atmosphere surrounds the Earth. Most of the air is within 10km of the surface and most of the atmosphere is within 100km of the surface.

The restless Earth

• The Earth's crust and upper mantle is cracked into tectonic plates which are constantly moving
• The tectonic plates move because of convection currents in the mantle that are caused by radioactive decay
• Earthquakes and volcanoes happen where tectonic plates meet, but it is difficult to predict accurately when and where earthquakes will happen
• Wegener's theory of continental drift was not accepted for many years

Scientists believed that the Earth was shrinking as it cooled, in the 1960s scientists found new evidence and the theory of plate tectonics was developed

The Earth's atmosphere in the past

• The Earth's early atmosphere was formed by volcanic activity
• It probably consisted mainly of carbon dioxide. There may also have been water vapour together with traces of methane and ammonia.
• As plants spread ocer the Earth, the levels of oxygen in the atmosphere increased

Scientists think that the Earth was formed about 4.5 billion years ago

As the Earth cooled most of the water vapour condensed to form the oceans

In the next two billion years, bacteria, algea and plants evolved. Algea and plants used carbon dioxide for photosynthesis and this released oxygen

Life on Earth

• There are many theories about how life began on Earth
• One theory states that the compounds needed came for reactions involving hydrocarbons and ammonia with lightning providing energy
• All the theories about how life started on Earth are unproven and so we cannot be sure how life began

The plants that produced the oxygen in the atmosphere probably evolved from simple organisms like plankton and algea in the ancient oceans

In 1952 two scientists, Miller and Urey, did an experiment based on what scientists at the time thought was in the early atmosphere. They used a mixture of water, ammonia, methane and hydrogen and a high voltage sprak to simulate lightning. After a week they found that amino acids, the building blocks for proteins, had been produced

Gases in the atmosphere

• Most of the carbon dioxide in the early atmosphere became locked up in sedimentary rocks
• About four-fifths (almost 80%) of the atmosphere is nitrogen, and about one-fifth (just over 20%) is oxygen
• The main gases in the air can be separated by fractional distillation. These gases are used in industry as raw materials

Nitrogen-78%

Oxygen-21%

Carbon dioxide- 0.04%

Argon-0.9%

Trace amount of other gases

Carbon dioxide in the atmosphere

• Carbon moves into and out of the atmosphere due to plants, animals, the oceans and rocks
• The amount of carbon dioxide in the Earth's atmosphere has risen in the recent past largely due to the amount of fossil fuels we now burn

Carboon dioxide dissolves in water, particularly the oceans, and reactions of inorganic carbonate compounds are also important in mainting a balance