Question: How did life start on Earth?

Iain Moal answered on 24 Jun 2010:

Wow. This is one of the biggest questions in science, and nobody knows for sure. However, there are some very good clues out there, and a lot of scientist believe the best condender theory for this is called the ‘RNA world hypothesis’.

There are a number of ways of looking at this quesition. Firstly, any contenter for the first living thing must have been able to be formed from non-living material available on the early earth. Seconly, it musy be able to self-replicate, with occasional mutations, so that it could evolve into more complex life. Finally, it must be able to do some life processes.

Now, RNA fill all these criteria. It can form spontaneously from material that was on the earth billions of years ago, and it can act as a template for the replication of itself. Futhermore, it can store genetic information, like DNA, and it can speed up chemical reactions, like proteins. In fact, people have managed to get RNA to evolve in the lab!

There is another good reason as to why I think RNA is likely the first living thing. If we look at all the thousands of molecular machines that living things have, from bacteria to beetroot to buffalo, there is one which is shared by all of them. It is called the ribosome. The ribosome is what turns genetic information into molecular machines. It is the most basic and essential thing for all life. Now, most of the machinery of life is made from protein molecules, but the ribosome is different. The ribosome is made from RNA. We know that proteins are generally better at doing things than RNA, so why would the most essential thing for life be made from RNA? The obvious reason is that it was originally made from RNA before proteins had fully evolved, and by the time proteins were used for things, life couldn’t go back. It was stuck with what it had, and it couldn’t change it because any changes would cause death. This, I believe, is one of the strongest bits of evidence that suggests that the way life started on earth was with a molecule of RNA which could replicate, which spontaneously appeared out of the random rearrangment of atoms.