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Earth began as a ball of dust, rock, ice, and stars in space 4.5 billion years ago. Gravity pulled this mass together. As Earth grew bigger gravity strengthened.
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4 billion years ago, as Earths surface cooled, water vapor began to condense to form rain gradually, rain began to accumulate, and form oceans.
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The oldest rock known,represents the chunks of earths crust, formed by molten lava that has erupted from earths cracks. The layers of the rock are formed by both new and ancient rock.
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Prokaryotic cells began to form 3.5 billion years ago. Prokaryotic cells are simple cellular organisms without a nucleus.
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Eukaryotic cells started to form 2 billion years ago. Eukaryotic cells are cells that have a nucleus. These are complex-cell organisms.
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Arthropods are invertebrates, with exoskeletons. These creatures developed 570 million years ago.