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The Earth has undergone numerous changes in both its land features and atmosphere over its history. The planet is probably about 4.5 billion years old. The first crustal land masses on the surface formed about 4 billion years ago. Some natural processes that have affected the surface crust include plate tectonics, volcanic activity, asteroid impacts, and glaciation. Plate tectonics are the motion of the crustal plates in the lithosphere. Where plates converge and subduct (one plate passes under another plate), mountain ranges form. Where plates diverge, oceanic trenches form. Volcanic activity has formed new land masses over time like the Hawaiian Islands. Asteroid impacts have left impact craters on the surface and brought unusual elements like iridium to the surface of the Earth. An asteroid impact is also the likely cause for certain mass extinctions in the planet's history, including the dinosaurs. Finally, Earth has gone through a handful of ice ages where a considerable portion of the planet was frozen over. Large ice masses called glaciers moved from higher mountain elevations to lower elevations over millions of years, thus carving deep channels into the surface and breaking up and depositing rocky masses along the way.
The atmosphere of the Earth has changed dramatically over time. The initial atmosphere during the formation of the planet would have been composed of the most abundant elements in the universe, hydrogen and helium. Over time, these light gasses would have been expunged and a process called outgassing from the cooling of the Earth would have replaced them with heavier gasses like water vapor, methane, nitrogen, and hydrogen sulfide. These gasses are greenhouse gasses and would have kept heat trapped on the surface of the planet, thus forming the first real atmosphere. Once early life (plants, bacteria) evolved on Earth, oxygen began to be introduced into the atmosphere in large quantities, thus introducing not only oxygen but also oxygenated gasses like carbon dioxide.
This is all accompanied by current phenomena like erosion that constantly alter the surface features of the planet.
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