Comment by Waterluvian | Hacker News Reader

Comment by Waterluvian | Hacker News Reader

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It’s a fantastic question this stuff isn’t intuitive.

http://mapdesign.icaci.org/wp-content/uploads/2012/04/atlant...

Consider this model: the Earth is like a puzzle. Its crust is made up of a bunch of pieces that all fit together. But those pieces aren’t unchanging. They all sit on top of a huge soft sludgey core called the mantle. And they want to slowly (slooooooowly) slide around.

At each boundary between pieces one of three things can happen:

- they slide against each other

- they diverge from each other

- they press into each other, often one going under the other, sometimes one pushing the other.

A continent can move, oh so slowly, over millions of years through a combination of shifting along with other plates, or having one side of its plate grow (move away and have the new gap filled with the molten plasticy goo underneath), while the other side pushes away a plate or disappears underneath the other plate.

The map I linked shows a massive stretch mark of the Earth in the Atlantic Ocean. This is one striking piece of evidence that the above effects have been happening over a long long time. It’s basically the boundary between a few plates. And it shows all this brand new ocean floor that came flowing up from under the crust (then cooled and got hard) when a gap was created because they separated apart.

Another thing to keep in mind: these tectonic plates are heavy. Like unimaginably heavy. They can be thousands of miles wide and tens of miles thick and are as dense as rock. They exert huge pressure on that soft sludgey core, which is incidentally being heated by a low-level nuclear furnace in the center of the Earth. So the plates are more like a lid on a boiling pot that is foaming over. They're all getting jostled by insanely powerful pressure from underneath. Every once in a while a pimple appears and goes kaboom.

Looking at New Zealand 35 million and 20 million years ago on that globe (search for one of our cities like Auckland or Christchurch) is really illuminating when compared to its current shape, most of the South Island is to the west of the North Island, as the plate boundary between the Indian and Pacific plate runs through the South Island, and the eastern side has been moving south-west for millennia to form the current shape of the land, and our Southern Alps.

Wow thank you for the explanation and that picture you provided makes it very clear as well. I did not realize that the world was divided into plates.

There's a BBC documentary on this that's now around 25 years old, called Earth Story (https://en.wikipedia.org/wiki/Earth_Story). It describes not only what we know, but how we know it. As documentaries go, it's rather in-depth but easily digestible.

Thanks for the suggestion, it sounds really interesting based on some YouTube comments. Just ordered it used from the UK, first time I'll be watching an actual DVD since... years. I think I do have a DVD drive somewhere in storage.

Good explanation.

To expand on that, earthquakes and volcanoes are the result of those plates colliding and separating.

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