The earth itself might not be a living breathing entity but it sure does house a lot of them. Have you ever stopped and wondered what life might be like if we never had the 5 major mass extinctions? Or how creatures on this planet would have evolved differently if our atmosphere wasn’t 78% nitrogen and 21% oxygen? What role did our atmosphere play in evolution anyway? I’m glad you asked…
The earth is approximately 4.5 billion years old and Homo sapiens (humans) have only been around for the last 200,000 years (that’s a mere 0.004% of the earth’s history)1. In that time, humans have managed to do a lot; create and destroy civilizations, habitats, animals, climate, technology etc. And we aren’t finished yet. Modern day humans are remarkable in that we are able to create a “false” environment for ourselves to live (think air conditioning or pumping in water to normally dry environments). But life hasn’t always been that easy on Earth. Earth was void of any oxygen until about 2.8 billion years ago and there wasn’t enough of it in the atmosphere to support larger life forms (multi cellular) until around 2.45 billion years ago2. Since there were no plants or trees around to create our oxygen based atmosphere, how did the oxygen get there? The work was done by tiny single celled eukaryotes called cyanobacteria (formerly referred to as blue green algae). These guys worked really hard to produce enough oxygen from the sun, through photosynthesis, to support any type of life. In fact it took another billion years for oxygen levels in the atmosphere to support the evolution of animals. This time has been dubbed the “boring billion” by scientists2.
We know approximately when oxygen first reached our atmosphere by monitoring reactions with other elemental compounds found on earth (oxygen is a great “reactor” meaning it creates a chemical reaction with just about every element found in the periodic table). Prior to that, the Earth’s atmosphere was mainly sulfur and was only capable of supporting single celled bacteria and archaea. This was around 3.8 billion years ago1. No one is quite sure how the atmosphere managed to balance itself out at 21% oxygen. Why didn’t our atmosphere stop at 15% or keep going all the way up to 50% oxygen? You have to admit, 21 is a pretty random number. But I can assure you that somewhere out there, someone is trying to answer that question.
After Earth’s atmosphere contained a little oxygen then the ball got rolling on larger multicellular life forms. Beginning with microorganisms, then arthropods, fish and eventually land plants. This of course was influenced by tectonics and climate. But that’s way beyond my expertise. If you are interested in learning more about Earth’s history, you can find an awesome website here (http://www.bbc.co.uk/nature/history_of_the_earth).
All of the living, breathing entities on this planet have evolved into what they are today because of our unique atmosphere, and proximity to the sun, which in turn created our climate. No other planet in our galaxy has yet to show signs of life similar to ours, although microbes are likely to persist. However, scientists have recently found seven potential earth like planets, three of which may contain the biomarkers for life. You can check out an article on the TRAPPIST-1 system here. If we do find life on other planets, it may help us answer some of the questions posed at the beginning of this post. https://www.washingtonpost.com/news/speaking-of-science/wp/2017/02/22/scientists-discover-seven-earthlike-planets-orbiting-a-nearby-star/?utm_term=.b86a1c88ce17
- Ecology book
- Biology book
- Google defintions