That post about soap a few weeks back was an oblique way of getting to my main point: that we are the beneficiary of a vast library of knowledge and assumptions that we no longer have to think about. I’d like to explore just how deep those assumptions go.
Let’s start at the beginning, about 4 billion years ago. This is a little bit after plate tectonics started, and a right about the time life started on this planet, or at least so they tell me. What I’m going to present in this series is rapid pass through of the history of life, as best ewe know. We know much less about what happened last Tuesday a thousand, a million or a billion years ago than we do today, but then again, no one was writing anything down then.
So, before I talk bout the history of Life, I need to talk about the history of Earth. Life started in the oceans, presumably, about 4 billion years ago (bya) but didn’t move onto land until 3.5 billion years later. The first fossil we have found is from 3.5 bya, so we had to use other methods to estimate the timing of life’s origins. This is not about that origin, but in all that happened since.
The setting of the oceans and that land affected the setting of life, especially once life became divided between land and sea habitats. The earth settled down in plate tectonics and oceans not long before the origin of life, so as long as life has been moving around on the surface of the Earth, the land has been moving around as well.
The 4-billion year history of plate tectonics is hard to portray, because along with land creation (rifting) comes land burial (subduction). Paleogeologists cannot study rocks dozens of miles under the earth, which limits their scope considerably. Therefore, the first continent we have any idea about came together by 3.6 bya: Vaalbara. The only extant parts of this continent are in Southern Africa and Australia. I have to skim the next couple billion years, though I’d bet they were every bit as action packed yet boring as life is today. Just multiply by 600, the number of short days in a year back then. The Earth’s rotation has been slowing ever since the Theian collision (4.5 bya.
Suffice it to say that Vaalbara broke up by 2.8 bya, by which time Ur (3 bya) had formed, then Kenorland (2.7 bya) formed and broke up (2.5 bya) in the relatively short span of 200 million years (from the early dinosaurs to today). Columbia supercontinent (2.5 bya) formed at about the same time and broke up by 1.9 bya. By 1.1 bya, supercontinent Rodinia had formed. This is the first continent that I could find a passable map of. It broke up by 0.75 bya and Pangaea began to form from the pieces by 0.36 bya (only 390 million years later, or back when the first spiders and scorpions colonized land, before insects had evolved). Pangaea (0.3 bya), which I’m sure a lot of you have heard of was one connected terrestrial mass, which broke up again after only a 100 million years (0.175 bya). By then, there were early forests, insects, amphibians, reptiles, dinosaurs, proto-mammals, and even proto-birds living on the shifting land masses.