The Origin of Life


First organisms
4-3.5 billion years ago

Nobody knows exactly when life began. The oldest confirmed fossils, of single-celled microorganisms, are 3.5 billion years old. Life may have begun a bit earlier than that, but probably not while huge rocks were still raining down on Earth. Life may have begun in warm alkaline vents on the seabed, or in open water, or on land. We don’t know, and we don’t know what the first organisms were like.

See other: History of Life

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One thought on “The Origin of Life

  1. The earliest life forms would likely not have left fossils and they originated in a nitrogen-rich atmosphere that would kill us today. The oxygen we breathe was created in the most surprising way – each tiny, single-celled creature, dying and decomposing, emitted the most miniscule amount of oxygen in the decomposition process. Over time – LOTS of time obviously, that oxygen released gradually polluted the nitrogen atmosphere (yes, polluted – a rose in an onion patch, however beautiful we might find it, is a weed), until many nitrogen-breathing organisms that didn’t evolve to adapt to the new oxygen atmosphere, died off, but a few evolved, adapted and survived.

    Despite the ancient age of the earth, and the fact that life appeared 3.5 billion years ago, it was only 600 million years ago that single cells found there to be an advantage in combining with other cells, and multi-cellular life began. At first, they combined to perform a particular function, then parted and went their separate ways – only later did they begin forming permanent clumps of cells with individual functions.

    As life as we know it didn’t begin until 600 million years ago, for slightly less than 3 billion years, single-celled life was all there was.

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