1. Amino acid make up all the proteins of life. Protein build all parts of all living things. Most amino acids contain the elements: Carbon, Hydrogen, Nitrogen and Oxygen. One way forward it to try to re-create the early earth conditions.

2. Miller – Urey used a mixture of water, ammonia, methane and hydrogen to model the early atmosphere. Under normal conditions these gases do not react together.

3. Miler and Urey used a high voltage to produce a spark to provide the energy for a reaction – simulation a lightening storm within this mixture. The experiment was run for a week.

4. After 1 week they looked at the mixture. It looked like a brown soup, in it they found 11 different amino acids.

5. This experiment provided evidence that it was possible to make the molecules of life from gases that may have been in our early atmosphere. Miler and Urey published their findings in 1953. They froze some of their experiments and stored it.

6. There are opponents of the theory that biological material can be made from non-biological material. They argue that the Miller-Urey experiment only works in the absence of oxygen.

7. Another theory is based on analysis of meteors that crash to Earth from space. In 1969 a meteorite fell from the sky above Australia, known as the Murchison meteorite, its mass was over 100kg. They found a range of organic molecules on it.

8. The latest studies of fragments of the meteorite have identified about 70 different amino acids. This shows that the molecules are capable of starting life on Earth might have originated from outer space.

9. Another source of biological molecules could have been deep under the oceans. Near to volcanic vents on the seabed we get both the conditions and chemicals needed.

10. The organic molecules, from whatever source could have formed a ‘primordial soup’. All the molecules needed to start life could have been in the sea. Then they would have had to react together to somehow make the first primitive cells. Protein molecules capable of replicating themselves might have been involved in this stage.

11. Others think that simple living organisms could have arrived on Earth in meteorites or comets. Their evolution had started elsewhere. This ‘extraterrestrial seeding’ from outer space supports the theory of life in other parts of the universe.

12. They believe that oxygen would have been present before the generally accepted time for its appearance. This would make any conclusions based on Miller-Urey of similar experimental results invalid.