What Was It Like When Life Began On Earth?

The planet has had life on it, in some form or another, for nearly as long as Earth has existed.

If you came to our Solar System right after it formed, you would have seen a completely foreign-looking sight. Our Sun would have been about the same mass it is today, but only about 80% as luminous, as stars heat up as they age. The four inner, rocky worlds would still be there, but three of them would look extremely similar. Venus, Earth, and Mars all had thin atmospheres, liquid water on their surface, and the organic ingredients that could give rise to life.

While we still don’t know whether life ever took hold on Venus or Mars, we know that by the time Earth was only 100 million years old, there were organisms living on its surface. After billions of years of cosmic evolution gave rise to the elements, molecules, and conditions from which life could exist, our planet became the one where it not only did, but where it thrived. To the best of our scientific knowledge, here’s what those first steps were like.

Life as we know it has a few properties that everyone agrees on. While life on Earth involves carbon-based chemistry (requiring carbon, oxygen, nitrogen, hydrogen, and many other elements like phosphorous, copper, iron, sulfur, and so on) and relies on liquid water, other combinations of elements and molecules may be possible. The four general properties that all life shares, however, are as follows:

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