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 The obvious reason is that it was originally made from RNA before proteins had fully evolved, and by the time proteins were used for things, life couldn’t go back.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.
Leo Garcia answered on 24 Jun 2010:
A simple question, but one which has puzzled scientists (well…. everyone really!) since we were first able to consider it. Scientists know a great deal about the kind of conditions under which life may have formed. The process is given the name ‘abiogenesis’, which means that life arose from inanimate matter.
The ‘building blocks’ of life are amino acids – and we know that these chemical compounds can form through natural chemical reactions. In life, these amino acids are organized into proteins which are constructed from ‘nucleic acid’ (sound familiar?). It is from these simple chemical reactions that the first self-replicating organisms first arose. After all, ‘life’ only entails replication and some form of metabolism – and given this plus time plus evolution… and you’ve got yourself a planet covered with life!
The first living things are thought to have been single celled lifeforms which formed perhaps around a billion years after the formation of the earth. We are amazingly lucky, because we actually have fossil evidence of this kind of simple life form:
So, scientists have a good idea of what kind of things would have happened for life to begin on earth – but the precise mechanisms that lead to the first nucleic acids is not yet known – although there are several hypotheses.
If you are interested in studying this fascinating (and very important) question, you could find yourself working at one of these places: