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Public question ask date: 2017-05-29 15:36:47
2019-04-26: No, it did not. It started somewhere in our universe.
Life is old. The dinosaurs are perhaps the most famous extinct creatures, and they had their beginnings 250 million years ago. But life dates back much further. The oldest known fossils are around 3.5 billion years old, 14 times the age of the oldest dinosaurs. But the fossil record may stretch back still further. For instance, in August 2016 researchers found what appear to be fossilised microbes dating back 3.7 billion years. The Earth itself is not much older, having formed 4.5 billion years ago. If we assume that life formed on Earth – which seems reasonable, given that we have not yet found it anywhere else – then it must have done so in the billion years between Earth coming into being and the preservation of the oldest known fossils. As well as narrowing down when life began, we can make an educated guess at what it was. Since the 19th Century, biologists have known that all living things are made of 'cells': tiny bags of living matter that come in different shapes and sizes. Cells were first discovered in the 17th Century, when the first modern microscopes were invented, but it took well over a century for anyone to realise that they were the basis of all life. You might not think you look much like a catfish or a Tyrannosaurus rex, but a microscope will reveal that you are all made of pretty similar kinds of cells. So are plants and fungi. But by far the most numerous forms of life are microorganisms, each of which is made up of just one cell. Bacteria are the most famous group, and they are found everywhere on Earth. In April 2016, scientists presented an updated version of the 'tree of life': a kind of family tree for every living species. Almost all of the branches are bacteria. What's more, the shape of the tree suggests that a bacterium was the common ancestor of all life. In other words, every living thing – including you – is ultimately descended from a bacterium. This means we can define the problem of the origin of life more precisely. Using only the materials and conditions found on the Earth over 3.5 billion years ago, we have to make a cell.
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