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Physical evolution. Late Proterozoic Era 600ma. Early Cambrian Period 550 ma. Late Cambrian 500 ma. Early Ordivician 485 ma. Late Ordovician 440 ma. Silurian 430 ma. Early Devonian 410 ma. Late Devonian 360 ma. Early Carboniferous 340 ma. Late Carboniferous 290ma. Late Permian 270 ma.
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3 Billion Years ago • More than 3 billion years ago, an amazing thing happened on Earth. Certain types of bacteria developed the ability to make their own food. These bacteria made food by using a process called photosynthesis. Using energy from the sun, the bacteria combined carbon dioxide and water to make food and oxygen.
The result • The oxygen that was given off had a big effect on Earth’s • atmosphere.
The iron sands • At first, the oxygen was taken up by iron that was in the ocean water. This caused the iron and oxygen, or iron oxides, to fall to the ocean bottom and form deposits of iron-rich sedimentary rock. • Eventually most of the iron in the oceans had combined with oxygen and fallen to the ocean floor.
Connection to you • Most of the iron that is used today to make cars and buildings comes from these deposits
Oxygen in the air • Now, oxygen that was produced by microbes was free to enter the atmosphere. As a result, the oxygen level in Earth’s atmosphere began to increase significantly about 2.5 billion years ago. Slowly, over hundreds of millions of years, the oxygen level increased to the present-day level of about 20 percent.
The buildup of oxygen in Earth’s atmosphere allowed the emergence of organisms that cannot exist without oxygen. Animals, for example, take in oxygen, combine it with the food they eat, and produce a waste product: carbon dioxide. • Plants then use the carbon dioxide as their food and produce a waste product that we need: oxygen
Continental MovementOver Time USGS Maps
Where are the himalaylas? • The greatest challenge for mountain climbers is Mt. Everest, whose peak rises 8,872 meters above sea level. This is the highest mountain in the world, though many mountains around it are almost as high. Mt. Everest is in the Himalayas, a series of massive ranges that extends 2,500 kilometers across South Asia north of India. The Himalayas cover all or part of the countries of Tibet, Nepal, and Bhutan.
Evolution of the himalaylas • A climber on the high slopes of Mt. Everest would probably be surprised to learn that the region was relatively flat about 40 million years ago. It was then that two continental plates collided. The plate carrying India had been moving northward for millions of years. The oceanic crust in front of it was slowly subducted under the Eurasian plate. But when the two continents collided, subduction stopped because India could not sink into the mantle. Instead, it pushed crust upward and downward.
Results of the impact • The Himalayas were one result. Thus, the Himalayas are actually pieces of plates broken and lifted up because of the collision. Another result of this collision was the movement of China eastward, as the movement of India northward pushed the Eurasian plate in front of it. The collision is still occurring today. In fact, the Himalayas are growing in elevation at a rate of about 1 centimeter per year.
