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Wonder - A Scientific Oratorio

The Earth
The Earth from space.
Credit: NASA

Theme 7 - Earth: The cradle of life

The earliest fossil evidence for life on Earth dates back to about 3.5 billion years ago. As soon as conditions on Earth were suitable for life to exist, we find evidence for life. So far Earth is the only place where we know life can be found, but there are so many stars, so many planets out there, that many scientists feel that life must also exist elsewhere in the Universe.

Studies of the fossil record show that the first very primitive life-forms appeared around 3.5 billion years ago, not long after the end of the Hadean eon. Before then conditions were so extreme on the young Earth that it is hard to imagine how life might have got a foothold. However, it clearly became quickly established when the rate of impacts dropped.

However, it was another 3 billion years before life evolved much beyond simple bacterial forms into more complex organisms, plants and animals, and eventually ourselves. In fact much of the basic complexity of forms of modern life was created in a short 5 million year period, about 570 million years ago, called the Cambrian explosion. The bacteria are of course still a very successful form of life.

The question of how life began is still unknown. We are also still unravelling the story of how it has developed and evolved since then. A major question which remains is whether life might exist on other planets. Searches have begun on Mars but as yet no life has been found there. We now know of more than 300 planets orbiting other stars and we think that most stars will have their own families of planets. In our Milky Way galaxy alone there are around a hundred billion stars. In the observable Universe there are around a hundred billion galaxies. We suspect life is out there somewhere.

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