Well here we are. We've come so far, about 10 billions years actually in just one post, but now we'll start to take it a bit more slow. Earth began to take real shape roughly 4.6 billion years ago, and at its origins was just a literal sea of magma and molten metals which sank to the bottom, a sea of fire if you will. At this point, there was absolutely no oxygen nor an ozone layer to protect us from the Sun's rays. However, that doesn't mean the building blocks for life were not already beginning to form in a very violent manner.
Thousands of meteors and asteroids and comets were crashing into Earth carrying one vital ingredient -- ice. To briefly expand on this, two very important things need to be stated. One, in the early Solar System, there was far more ice and more importantly, more Comets, in the inner Solar System that could potentially have hit Earth and in fact computer simulations show that purely Comets could supply the necessary water on Earth. Secondly, with recent discoveries, we have also found that it could very well have been the case that many Asteroids then and now were/are rich with ice that could also have contributed to the adding of water to Earth's surface.
Nonetheless, it's not like these guys just crashed into Earth and BAM oceans! As we discussed earlier, it was rather heated on Earth's surface. So this ice was turned to Steam and released into the forming Atmosphere, to which it would condense and fall down and be annihilated by meteor storms and the intense heat of this Earth. At the same time, as metals began to sink, a very basic crust began to form -- as thin as paper as the Earth cooled. At the same time, a liquid iron Outer Core took shape and created the electromagnetic field that would help protect us from the Sun's deadly rays. Suddenly, the Earth doesn't look as horrible anymore.
About 3.8 billion years ago, the impacts began to slow and the heat was taken down a notch as water could begin to permanently form on the surface. Now this is the cool part. Early Earth was dominated by Carbon Dioxide, and as such, life began to form. Wait, what about Oxygen? Oxidized Oxygen was not yet formed (well, abundant) in the atmosphere and if it was present? Life would not have been able to form! You see, Oxygen in its molecular form, would prohibit life from forming because of its extremely reactive qualities.
And now, we get the origins of life. Molecules in the next 300,000,000 years would begin to react with each other, and in reactions that were completely abiotic began to form the complex proteins and enzymes needed for life. These chemical reactions continued until roughly 3.5 billion years ago, when the first single celled cyanobacteria formed and rapidly reproduced.
Not nearly as epic as my other pictures, but this is your greatgreatgreatgreatgrandfather -- so be respectful!
Fueled by the Sun, basic photosynthesis began to take place and the origin of our oxidizing Atmosphere. Even though massive amounts of Oxygen were being produced, it does not mean molecular oxygen was still present in our Atmosphere yet. In fact, early Earth's atmosphere was LOSING Oxygen faster than it was gaining it. Why? Not because there was a shortage of Oxygen per se, but because of "oxygen sinks". Especially in our crust, enormous reserves of reduced elements were present (I hope you remember those from your Chemistry Class!), which kept absorbing all of the Oxygen that was being created.
However, as roughly 1.5 billion years passed these reduced elements were fulfilled, and suddenly there was not much else that needed the Oxygen being created by the bacteria and as such -- molecular oxygen began to form. Almost 2 billion years after the first Bacteria formed, actual Oxygen began to fill our atmosphere. At this point, two VERY important things are true:
1) Oxidation of the Atmosphere over this time led the Earth to reach its current levels of a roughly 20% ratio.
2) Massive amounts of O3 (Ozone) began to form and form a primordial Ozone Layer, which would continue to form and increase until it reached the level of which we have today.
Now I know basic math shows that we are at 2 billion years ago at this point, but let's jump back 500 million years and look at the history of tectonics on our Earth. This is the part where I cheat, because this is something I feel needs to be shown rather than visualized.
And this is when I leave you. I know it's a rather short blog, and I probably could have been a bit more dramatic but meh. I want to spend a lot of time on early life specifically, the Cambrian explosion, the different eras, dinosaurs, and all that fun stuff. Once I spend 1-2 more blogs on the history of life up until now, I'll begin to write on more abstract concepts and hopefully write far more in depth blogs on matters such as Dark Matter, Black Holes, different theories for the beginning of the Universe, Intelligent Life in the Universe, so on and so forth.
Also, a cool .gif I found on google. Oh, and as usual, please know this is an extremely condensed version of events and by no means supposed to be an academic paper or anything of the sort. Some numbers may be off, some ideas may be a bit wrong -- I fully realize this and I actively encourage you to come in and tear my post apart to correct me as I adore being corrected. However, keep things constructive please