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Aristotle first compiled and expanded the work of prior natural philosophers and the various ancient explanations of the origin of life leading to the the theory of Spontaneous Generation. This theory swayed for as long as two millennia
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During the 17th Century, all over the world, mankind was formulating recipes to "create" organic life from inorganic matter. e.g Take sweaty rags, wrap them around wheat, and set them in an open jar. In 21 days, you'll "create" mice.
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Francesco Redi, an Italian scientist, opposed the idea of spontoneous generation and thus designed a scientific experiment to test the idea that maggots were generated from rotting meat. He placed meat in three flasks, one open, one sealed and one with a filter. Maggots appeared in the open flask, but didn't appear in the sealed flask or the flask covered by gauze. He believed this disproved spontaneous generation. However it didn't, it only proved that flies don't come from meat.
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In the 1700s the microscope finally became widely used within scientists to prove expiriments and to observe small living things (microbes) within liquids like broth.