When a big earthquake hits, it can be devastating-entire cities can be levelled, not to mention the loss of human lives. So what is going on when the ground starts shaking beneath our feet? To find out we need to go deep underground. At the centre of our planet-around 5,000 to 6,000 kilometers beneath the surface-is an extremely hot, solid core, made mostly of iron and possibly nickel surrounded by a molten outer core (also thought to be made of mostly iron and some nickel.
But unlike a smooth eggshell that you may imagine, the Earth's crust is not a single, unbroken layer. Rather, it's made of sections called tectonic plates that sit on top of the slowly flowing and moving mantle. These plates do not stay sti ll: over time, they migrate around the planet, sometimes grinding against each other, or pushing into each other to build mountain ranges. In other places where plates are moving towards each other, one plate is forced underneath another plate. The results are known as subduction zones, and the world's largest earthquakes occur in these regions.
With all this dynamic movement constantly taking place all over the planet, big plates of rock moving around and bumping against each other, it's no wonder that sometimes it gets a little unstable. As the plates move relative to each other, huge amounts of stress can build up over long periods of time. Eventually there comes a point when all the accumulated stress is suddenly released: rocks break and huge sections of crust are cracked and displaced. These movements result in waves of energy called seismic waves that radiate out in all directions. The waves travel into the interior of the planet and towards Earth's surface. All this activity takes place deep within Earth, making it difficult to monitor and, therefore, difficult to predict when a future earthquake might occur.
Adapted from: https://www.science. org.aulcurious/earth-environment/what-causes-earthquake
The passage mainly talks about
(A) the destructive impact of earthquake to the loss of human's properties.
(B) the continuous moving of tectonic plates which endangers human civilization.
(C) the ever moving earth crusts leading to the occurrence of natural disasters.
(D) the occurrence of earthquakes triggered by the movement of tectonic plates.
(E) the constant movement of seismic waves causing destructive earthquakes.
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