One of the scientists I most admire is the famous astronomer Carl Sagan (now deceased). In order to help people understand just how far apart on a time scale events in the Universe are, he popularised the “Cosmic Calendar”.
If you have time you should watch ‘Cosmos: A Space Time Odyssey’ – it is an amazing programme. Check it out on the link below,
If the history of the universe is compressed into one calendar year, with the ‘big bang’ happening on Jan 1st, every month in the cosmic calendar represents about a billion years, the milky way disk appears in May, our solar system appears in September and life follows that.
Wow! Amazing question, but impossible to answer to its fullest in this format :-).
It is currently hypothesised that life on earth started in a primordial soup of chemicals and first was all based on RNA molecules – the so-called RNA world. Life as we know it soon followed.
To learn more about the RNA world check this wikipedia link and enjoy:
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