The Origin of Life
Life on Earth seems to have evolved continuously for at least 3,800 million years, punctuated by intervals of mass extinction. The very earliest cells were probably archaea-like, tolerant of hot acidic conditions and an oxygenfree atmosphere. Continual changes in DNA generated novel organisms, which were subject to rigorous selection by the environment. Some survived and became established, altering the chemistry of their surroundings. The environment changed. Photosynthesis opened the door to the evolution of oxygen-using organisms and consumers. Symbiosis fused disparate genomes into new and ever more complex living forms. Single-celled eukaryotes emerged, then multicellular organisms, then animals and plants. Sexual reproduction appeared, food chains were born, the land was colonised. As a result, a huge diversity of species inhabits the world today.
KeywordsHydrothermal Vent Protoplanetary Disc Spontaneous Generation Meteorite Impact Iron Sulphide
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