Origin of oxygen
The origin of oxygen in Earth's atmosphere derive from life. Ancient microbes first produced oxygen through photosynthesis. Initially, scientists believed that the origin of oxygen on Earth began with photosynthesis microbes called cyanobacteria .
picture of cyanobacteria
However, a new study showed that photosynthesis originated a billion years earlier than previously thought which means oxygen was available for living organism close to the origin of life on Earth. Researchers studied the molecular machines responsible for photosynthesis and find that photosynthesis may have occured more than 3.4 billion years ago.
picture of photosynthesis
This is long before oxygen or cyanobacteria were thought to have enlisted on Earth. This means there must have been predecessors, such as ancient bacteria that have evolved to carry out photosynthesis and produce oxygen. Even though tiny microbes were producing the gas as a byproduct of photosynthesis. Earth's early atmosphere and oceans were devoid of free oxygen. Free oxygen doesnot combine with other elements such as carbon or nitrogen. Much of the oxygen produced reacted with iron, sulfer and other chemicals in the oceans an in the rocks on Earth's surface. As a result, Oxygen entered into seafloor sediments and eventually into earth's interior.
picture of old earth and new earth
About 2.4 billion years ago oxygen in the atmosphere suddenly increased by about 10,000 times in just 200 million years. This period is known as the Great Oxidation event which changed chemical reactions on the surface of the Earth completely. At the same time when free oxygen started to accumulate in the oceans, changes occured in the composition of Earth's crust. Before oxygenation, rocks on earth contained a mineral called Olivine .
picture of olivine
Research shows that when olivine comes into contact with water it initiates chemical reactions that consume oxygen and lack it up. However, as the continental crust evolved to a composition more like today's. Olivine virtually disappeared from earth's crust. Without that mineral to react with water and consume oxygen the gas was finally allowed to accumulate oceans eventually became saturated and oxygen crossed into the atmosphere.
picture of oxygen
This is how the oxygen is originated on Earth.
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