The Theory of Nothing

What the heck is plate tectonics?

What the heck is plate tectonics?

It's hard to believe that not that long ago geologists didn't understand that the Earth's lithosphere (the crust and upper mantle) is broken up into separate plates that move or float on the visco-elastic solid lower mantle layer (called the asthenosphere) independent of one another. There are seven major plates: African, Antarctic, Eurasian, Indo-Australian, North American, and South American. There are also eight secondary plates and a bunch of Tertiary plates.

The reason they're called tectonic (a Greek word that means building process) plates is because they are associated with the building of the land above the seas. Tectonic plates are also responsible for mountains and ocean trench formation, as well as causing earthquakes and volcanic activity. All of these things are why geologists are so interested in them. Tectonic theory also helps us understand how the Earth developed to what we see today.

The location of the boundary of two plates (where they touch) is important because it's where all the action is. Three different things can happen at these boundaries. In one case two plates may move alongside of each other, literally sliding or grinding as the case may be. In this case the boundary is called a fault line and it's how some earthquakes happen. The rubbing or grinding action causes huge vibrations that radiate out for hundreds of miles. These vibrations can knock over building and destroy property. In some cases the landscape is altered. This is what happened to Nepal in April of 2015. This is the result of India crashing into Asia. Tension builds up over many years and then breaks to cause a devastating earthquake.

The second case is where two plates slide away from each other, often causing a huge trench or rifling effect if it occurs in the seabed. In many cases this causes two continents to separate by a greater margin. This type of tectonic action can cause volcanoes.

The third case is where two plates crash into each other. One plate could slide under the other in what's called a subduction. This action lifts the other plate and forms a new mountain range. The Andes were formed this way. Subduction can also form islands. Japan was formed this way.

The question you might ask is: what the heck causes this tectonic action? This is where we get into the theories of tectonics, and the theories are not necessarily in agreement. The two things we can deduce for certain is that the lithosphere is harder than the underlying asthenosphere and that the heat from the mantel is the cause of this plate movement. But how does it work?

One answer is that there are convection currents in the mantel, but it is not completely understood how this works. One idea is that there is a drag effect caused by friction between the lithosphere and asthenosphere. Another idea is that the plates are sucked down in subduction zones at ocean trenches. It's as if the plates act like slabs and are tilted down by this sucking action, which is blamed on gravity.

Gravity is thought to play a part in tectonics, but some believe that it's enhanced by Earth's rotation. In this case it's thought to be like a tidal force that varies from the Earth's poles to the equator.

Whatever the theory, we are definitely riding on plates that are like giant ships on an ocean of thick gooey mantel stuff. We're not moving that fast, but the motion is inexorable and the inevitable result is that we in the Americas will end up in Africa, more or less where we started out.

Thanks for reading.