Supercontinents or how we are all going to the Arctic
When Earth was born…
Around 4.5 billion years ago, Earth was born from a turbulent accretion disk of celestial gases and clouds of dust with help from gravity, the glue to hold everything together.
Soon after that, Earth was bathed in some serious celestial showers made of asteroids, meteorites and comets (The Late Heavy Bombardment). Our neighbor rocky planets like Mars and Venus had the same fate too. In one occasion, an astray asteroid called Theia collided with Earth, and here came our Moon.
At first, the only thing going on Earth was just a vast ocean of magma and maybe several tremendous tides. These tides were much more enormous than today because Earth was much closer to the Moon.
Then there were some tectonics activities as well. As a result, some crusts were formed and some maybe were submerged into the magma ocean. The tectonics was busy but stagnant in terms of creating stable crusts because of the super hot magma ocean then(drip tectonics).
Then it started to moving around…
Little by little, some crusts were finally formed as Earth was cooling. Oceans were shaped too. Then continental drift kicked in as plate tectonics.
Basically, there are 3 types of relative movement between plates:
- Divergence: plates move away from each other. As a result, the crust at the plate boundary is stretched out and become thinner. Then the crust pressure against the underlying upper mantle(Asthenosphere) slowly declines. Hence the solid but plastic mantle rock below becomes molten partially to create a magma chamber due to decompression melting. In the end, the crust pressure is unable to balance against the pressure of the rising magma. Consequently, magma rises up to or near the surface and can lead to volcanic activities.
- Convergence: plates collide into each other. 2 things can happen. If both plates are continental crusts, they will mostly crush into each other and stack up into mountains. If one of the plates is an oceanic crust, the denser and heavier one (mostly the oceanic crust) will sink down into the other one and create a subduction zone. As a result, some water from the oceanic crust is mixed and burned up with the underlying mantle rock due to flux-induced melting. A magma chamber is formed, which gives rise to volcanic activities.
- Transformation: plates can slide past each other. When this happens, rocks at the boundary is pulverized into pieces and create a linear ridge(fault zone). Earthquakes are common during this period.
Tectonics is thought to be caused by multiple forces. The biggest one probably is from the mantle due to the unceasingly moving up and down of the super hot mantle rock because of heat convection. The second biggest one may be the force created by the slab pull from the subduction zone.
Then came the Supercontinents…
For some times in the past, all those plates gather into a giant continent — a super-continent.
Sometimes, that super-continent clumped around the Equator. Other times, it began to break into smaller chunks and then drifted away again in order to gather again some time in the future. This activity of drifting away and clumping into each other has been making many changes to the topology of Earth.
There was many super-continents in the past. One was formed around 2.1 billion years ago called Columbia. Then it broke up and formed again the super-continent Rodinia around 1.2 billion years ago. And then it broke up again to create another Pangaea around 250 million years ago.
Some scientists suggest that there is actually a Super-continent cycle that happens every few hundreds of million years. But what will happen in the next few million years is anyone’s guess.
How do we know?
There are many evidence that prove tectonic plates are a real thing.
- Continental boundaries of South America and Africa can fit together just like a jigsaw puzzle. It may not be a coincidence.
- There are some similar species of flora and fauna that lived at the same time in very different locations, which means their locations must have been next to each other sometime in the past.
- The mid-ocean ridges are the result of the sea floor spreading, which means some plates are moving away from each other.
So where are we going?
Scientists really do not know exactly how the face of Earth ages.
The tectonic plates can either keep drifting away as they’re doing now. And then we would have ended up clumping into one giant mass the other way around(extroversion). Hence there would be only the mighty Atlantic surrounding us. The Pacific Ocean may have been gone completely then.
Or all the plates can turn around sometime in the future and start to rush into each other(introversion). The Atlantic Ocean would be closed and the Pacific Ocean would embrace all of us then.
Some strange ideas are also put forward that we may all go north and get together to set bonfires through harsh winters of the Arctic(orthoversion).