Question: How much has the earth changed since the big bang?

Susan Cartwright answered on 19 Jun 2015:

Well, for the first 9 billion years after the big bang, the Earth did not exist at all, so that’s a fairly large change.

The first generation of stars formed after the Big Bang are no longer around today – they were very massive, and they all exploded long ago. The oldest stars we know of probably formed a few hundred million years after the Big Bang, but our Sun formed much later. This is a good thing, since all the elements from carbon onwards are only produced in stars, and therefore several generations of stars had to live and die in order to make the elements of which the Earth – and ourselves – is mostly made up. A star from the first generation after the Big Bang probably wouldn’t have had planets at all.

The main change in the Earth since it solidified from its original formation is in its atmosphere. It started with an atmosphere mainly of carbon dioxide (as Venus still has). The CO2 mostly dissolved in the oceans to form carbonate rocks, leaving us with an atmosphere of nitrogen (like Saturn’s moon Titan). Finally, photosynthesis evolved and released oxygen into the atmosphere, so about 2 billion years ago the atmosphere finally eveoled to the nitrogen/oxygen mix it is today.