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Scientists can date the fossils back by one of two methods. The first method is relative dating. This involves corresponding the rocks around the fossil to appropriate dates, it is usually an educated guess. Another method is radioactive dating. This involves carbon 14. They look for the half-life decay rates of radioactive isotopes and can find the year of the fossil from there.
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Scientists found the oldest rock known and dated it back to when the Earth was most likely created.The Earth may be older than we think but until we can find an older rock we will estimate that the earth is about 4.374 billion years old.
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Scientists don't exactly know how and when water appeared on Earth but most believe that the Earth was struck with wet comets and asteroids.
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Alfred Wegener, scientist, believed that the continents had shifted because of fossil and rock evidence. We can tell that oceans used to be in specific areas because of the fossils found there. Example: an ocean dweller's fossil was found on top of a mountain.
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Scientists have found remains and evidence of what the climate was like in the past. Salt deposits and fossils can be found in glaciers which are then dated.
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Scientists can date the fossils and remains of an organism and trace it back to when they were alive. Most of the time when dating it is an educated guess or a range.
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Scientists find two or more organisms that have similar traits. They date the remains to see if their ancestors were from the same time.
