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FOSSILS ET AL
Where Did All the Oxygen Come From?
How Early Cyanobacteria Transformed Earth’s Atmosphere and Shaped the Evolution of Life
Take a deep breath in. The air you are breathing is essential to life as we know it. It varies a bit from place to place, but it’s probably about 78% Nitrogen, 21% Oxygen, 0.9% Argon, 0.05% Carbon Dioxide, and a lot of other minor gasses that make up the rest. We humans have specifically evolved to thrive with this combination of elements in the air. Minor variations, like going up in elevation or humid days with lots of water, are okay. But, any large deviation from this ratio and we won’t last long.
However, our planet wasn’t always this way. The early Earth formed as a swirling mass of dust that existed about 4.5 billion years ago. As it slowly condensed into a planet, its atmosphere was mostly methane and ammonia. This combination is also found in our Solar System’s gas giants like Saturn and Jupiter. As you might guess, these gasses are toxic and very dangerous for most life. We would die almost instantly if we breathed in those atmospheres.
As Earth’s crust solidified, the surface gradually began to cool. Water vapor began to rain to the surface as liquid, and here we see Earth’s ocean forming. During this stage, Earth was almost entirely covered by water. The tectonic plates are now beginning to operate and causing extreme volcanism all over the planet. This volcanic activity, along with frequent asteroid collisions, drastically changed the atmosphere of early Earth. Now, the composition looks a little more familiar. Methane and ammonia levels go down, while carbon dioxide and nitrogen become much more common. But where is all the oxygen?
The changes I have mentioned so far all have happened due to massive collisions, planet formation, and our terrestrial volcanic activity. These events bring new elements into play and drastically shape the atmosphere. In…
