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Earth was formed around 4.5 billion years ago, and it would be around 500 million years until life began to evolve. The Earth was formed by accretion from the solar nebula.
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Life was first discovered around 3.8 billion years ago, a little before oxygen entered the atmosphere. The first organisms that were found were prokaryotic, which do not need oxygen to survive, as they can use aerobic cellular respiration.
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Approximately 3.5 billion years ago, oxygen was thought to have enter the atmosphere. The first organisms on the Earth that were supported by oxygen were blue and green prokaryotic algae organisms, which converted sunlight to oxygen using photosynthesis.
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2.7 billion years ago, eukaryotes were formed. This was after prokaryotes were formed and because of this, eukaryotic cells had oxygen and food to live, and they soon developed from 2 celled organisms to more complex organisms.
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Around 600 million years ago, multicellular organisms were first discovered. Before that, there had only been prokaryotic cells, which did not need oxygen to survive. The prokaryotes helped the eukaryotes live because they used the Endosymbiont Theory to survive off the prokaryotes.
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During this mass extinction around 430 million years ago, 86% of life on Earth at that time was wiped out because of falling sea levels and glaciation. Scientists believe that the cause of this was that there were too many plants that were using up carbon dioxide and not enough animals that were using oxygen.
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This mass extinction caused around 75% of species to become extinct. Two proposed causes of this extinction were that there were many volcanoes, which released their ash and lowered the Earth's temperatures and that there were a lot of large plants which used up too much of the Earth's nutrients. If this extinction had not happened, humans would most likely not be alive.
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Pangaea was formed around 270 million years ago, which is was closer to the current day than to the creation of the Earth. At this time most of the dry land on Earth was joined into one huge landmass that covered nearly a third of the planet's surface. It broke apart around 70 million years later
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The Permian-Triassic extinction is considered the worst ever extinction because it killed 96% of the organisms and species on the Earth. This was because of a great volcanic eruption and new bacterial organisms produced too much methane and carbon dioxide. Although this killed many entire species, more complex marine species such as crabs and snails were formed.
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Around 200 million years ago, Pangaea broke up after being together for 70 million years. Because Pangaea broke up, the area split into continents such as North and South America, Europe, and Africa.
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This approximately 15 million year extinction had several species loss. Asteroid impact, climate change, and flood basalt eruptions were blamed for the extinction. During the beginning of this era, mammals outnumbered dinosaurs. By the end, dinosaurs outnumbered all other animals on the earth’s surface.
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This extinction happened around 65 million years ago, and although it was not the longest or biggest extinction, it is the most well known because it characterized the killing of dinosaurs. A combination of volcanic activity, asteroid impact, and climate change ended 76% of life on Earth. This extinction period allowed for the evolution of land mammals.
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Around 2.5 million years ago, humans first began to develop on the Earth. They began as undeveloped apes and became more developed and eventually progressed to where they are now.
