Well evolution and life go hand-in-hand, so as soon as life begins so does the start of competition! And it’s competition that causes evolution.
So estimates of when life started are about 3,500 million years ago! But as there aren’t any records of life these estimates have been made based on our knowledge of the environment on earth at the time. We are not even sure what exactly caused life to just start!
And when exactly does something become ‘life’… it’s a surprisingly difficult question to answer :s
As Cassie stated, the first living organisms fossilised ~ 3.5 billion years ago. But this is what formed fossils, things like bacteria and viruses won’t have fossilised (at least noticeably).
The first ever fossils are of Stromatolites, which are dated at 3.5 billion years. These are layers of sediment built up by layers of a type of bacteria. They can still be seen today in Western Australia. I plan to visit one day.
But the first ever piece of RNA??? Or first ever sugar?? Who knows, maybe we can find out through some clever means one day.
I wish we could answer to that 🙂 unfortunately our records are limited from the things that leave a trace, like fossils (but only certain things fossilize and only in very specific conditions!), sediments (through elements decay)…all the rest are just estimations, from how long we think it would have taken! The current estimations are exactly what Tommy and Cassie, and from that point on, as soon as natural selection started taking place and only the fittest would survive…so most likely evolution would start straight away!