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 • Basic Overview
The First Forms of Life
The first life was single-celled. By 3.5 billion years ago, tiny single-celled organisms called prokaryotes were living in Earth’s oceans. We find fossil evidence of these organisms in some of the oldest rocks on Earth’s surface. These ancient rocks, found in Australia and Greenland, range from 3.8 billion to 3.5 billion years old.
There is much we don’t understand about how these living cells first formed from organic compounds. But we do know that life had begun. Cells were using energy, growing, reproducing, and dying: this is life.
 For around one billion years, prokaryotes were the only life on Earth.
Though prokaryotes share the planet with many other life forms today, they are the most ancient form of life—and the most common. Prokaryotes far outnumber all other life forms, thriving everywhere from the ocean’s depths to our own intestines. Eventually, these tiny bacteria changed the world.
To view more images of these organisms, take a look at the Early Organisms Image Gallery.
Or, continue to Light and Early Life. >>
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