- 3619 - EARTH’s - oxygen through the Ages? Animal life has at least 4 things it needs: food, drink, reproduction, and breaths. All but the breathing can be put off for days, weeks, years, but you better breath in seconds. Nothing kills an animal quicker than lack of oxygen.
--------------------- 3619 - EARTH’s - oxygen through the Ages?
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- The Earth did not have oxygen in its atmosphere between the time of its birth 4,500 million years ago and 2,200 million years ago. Without oxygen there is not much chance for life on Earth.
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- Even 2,200 million years ago when oxygen first appeared in the atmosphere there was not enough to support animal life. It was the plant life, algae, in the oceans that slowly built up the Earth’s oxygen levels over millions of years. It was not until 600 million years ago that there was plenty of oxygen for animals.
- The oxygen levels varied significantly over the millions of years. Today it is at the 21% level. Much of the evolution of life can be correlated with the level of oxygen in the atmosphere:
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-------------------- zero million years ago ------------ 21%
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-------------------- 100 million years ago ------------ 18%
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-------------------- 200 million years ago ------------ 15%
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-------------------- 300 million years ago ------------ 30%
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-------------------- 400 million years ago ------------ 13%
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-------------------- 500 million years ago ------------ 17%
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- Plants and algae put the oxygen into the atmosphere but oxygen is a highly reactive element and it leaves the atmosphere combining with the other elements. Oxygen quickly attaches itself to iron, sulfur and carbon. Reduced iron becomes iron oxide and turns to rust.
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- Oxygen gets back into the atmosphere by the reduction of these oxidized compounds. Photosynthesis turns carbon dioxide back into carbon and oxygen. And, there is the circle in nature. Photosynthesis is the breathing process for plants. We breath and burn carbon to reverse the process. It is the balance between these two processes that determine the amount of oxygen in the atmosphere.
- Between 400 and 500 million years ago the oxygen levels increased from 14% to 24%. 500 million years ago the first land plants appeared. And 425 million years ago animals first came out of the oceans and began to inhabit the land. They were small scorpion like animals that had been living in the oceans for over 100 million years.
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- Today there are some 100 lineages of fish that show some adaptation to terrestrial life. Animals were 75 million years behind the plants most likely because they had to wait for the oxygen levels to rise enough to allow lungs to function.
- Oxygen levels fell back to 13% at the 400 million year mark. This resulted in a mass extinction of life and many animals returning back into the seas. Between 300 and 400 million years ago oxygen levels again rose from 13% to 30%.
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- Land animals became common again 345 million years ago. Between 200 and 300 million years ago oxygen levels again fell to 12%. Reptiles were the dominant animals at the time. They first appeared about 300 million years ago.
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- The first dinosaur lungs were small, rigid and sac-like that adapted well to 30% oxygen levels but did not work well in thin air . Even today’s lizards do not thrive at higher elevations and are rarely found above 2,500 feet elevation.
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- Mass extinctions occurred with the 12% oxygen levels and better lungs soon evolved. 230 million years ago lungs evolved to have supplementary air sacs that were much more efficient. These new lungs were invented by the dinosaurs.
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- We see these lungs today in birds that can fly over the tallest mountains at elevations that would kill us humans. When a bird breaths air it enters the air sacs and is stored briefly before the lungs exhale. The result is more efficient gas exchange between air and blood. Birds are 33% more efficient the mammals at sea level and 200% more efficient at 3,000 feet elevation.
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- From 200 million years ago till today oxygen levels have steadily increased from the 12% to 21% levels. When oxygen levels increase we owe it to the plants. When oxygen levels decreased it was most likely caused by the tectonic forces that cause mountains to rise bringing new reduced compounds to the surface were they would absorb oxygen out of the atmosphere. The opposite can occur if a tectonic plate dives beneath another. That what happened when vast forests became buried in coal swamps.
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- How do we know these oxygen levels throughout prehistoric times? There are two ways:
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- First, by drilling ice cores in the Antarctic. Scientists have drilled down over 3 kilometers taking samples over 740,000 years. They plan to drill further and sample air bubbles in the ice that is over 900,000 years old.
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- The second method is measuring the about of oxidation in rocks, particularly iron, that is buried at various levels of time. No oxidation can be found at all in rock that is over 2,300 million years old.
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- There is no question that oxygen has played a significant role in the evolution of life on Earth. We are just now beginning to line up its history with the evolution of prehistoric animals.
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July 4, 2022 EARTH’s - oxygen through the Ages? 808 3619
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