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You hear a lot about people who believe the world is flat these days. It is hard to think of anyone who seriously thinks that the world is not a world. But, in researching a new work about life and history, I found a whole new meaning for a “flat earth,” or a “spread earth,” that has a chance of being true. To understand what I’m talking about, we need to go back to a geological sequence: plate tectonics.
Plate tectonics
The lithosphere is the scientific name for the outer layer of the planet. It goes down a few hundred kilometers and includes both the bottom and the top. The important thing about the lithosphere is that it is hard, unlike the deepest part, which, over time, flows like taffy (or, as one researcher says, it like asphalt on a hot day). The movement of the deep mantle involves large eddies called convection. On Earth, unlike other rocky planets such as Venus or Mars, the lithosphere is broken into a bundle of plates. These plates seem to float on top of the lower mantle, moving along with the movement of the mantle. Sometimes these movements lead to the plates moving away from each other. But in other places, the plates collide, and one plate sinks into the deep mantle (a process called subduction) while the other plate pushes up. As the plates move, so do the continents, which are made of marble (unlike those of the iltitai which are made of basalt).
All of this sliding, subduction, and collision is the reason why the Earth’s map has been continuously rewritten over hundreds of millions of years. Supercontinents such as Gondwana and Panagia have converged and broken up, closing entire oceans and opening new ones. All these transcontinental migrations had a profound effect on life. The tribes that lived together found themselves a few million years later as horizons opened up and the land was divided.
Equally important, collisions between tectonic plates are what drove the world’s great mountains such as the present-day Himalayas. Mountains affect life and its growth in many ways. Most obviously, they can act as natural barriers to the movement of untapped species. It is unclear, but perhaps more important, that these high mountains are prone to extreme weather conditions, which are gradually eroded by wind and rain. All those minerals from the eroded mountains eventually find their way to the ocean where they can serve as nutrients for life to use for its various molecular needs.
This introduction of mountain weather to the biosphere is something I’ve been interested in for an astrobiology project I’m working on. In the process of researching that research I discovered something interesting: The earth did not always have plate tectonics, especially the kind that exists today..
As I wrote above, other terrestrial planets do not have plate tectonics at all. Instead, their lithospheres consist of a “single cover.” On Mars, for example, there are no plates and there is no plate movement. In the beginning, about 4 billion years ago, the earth may have had a single lid that was only slowly breaking apart. Equally important: Although there were separate plates two billion years ago, they did not move as they do today. In particular, the whole defeat and collision thing could have been dumber. According to the research papers I’ve read, the kind of active plate tectonics we see in the modern world is probably a recent phenomenon – only a billion years or less. (Yes, I know, it’s weird to think of a billion years as “news,” but it’s geology, after all).
An exciting World
So why is that important? Mountains…big mountains. Without the modern process of plate tectonics, there would be no great mountains like the Himalayas. While there may have been twists and turns, small climbs – the kind of long, high ridges we think of as the most dangerous and spectacular places on Earth – it is not possible.
It’s amazing to know that the earth, for the first three or so billion years, was not flat – but rather it was flat.