Earth’s Changing Face
EARTH’S CHANGING FACE IS AMAZING
By: Muhammad Mujtaba
EARTH’S CHANGING FACE IS AMAZING ;Geologist has long known that the earth’s crust has cracks in it. However, they used to think that the crust was all in one piece. Today the concept has changed, and it is now established that the outer shell of the earth, which is made up of crust and rock from the upper mantle, is broken into big pieces or plates.
There are ten or twelve big plates and some small once. Each plate is about 96 km thick floating on the very hot rock below. These plates are in motion, through the motion is very slow, i.e. 5 to 7 cm a year on the average. As they move, they carry along whatever is on top of them the ocean floor, island, and whole continents.
Earth has started changing its face from millions and millions of years ago, these landmasses have drifted, sometimes colliding and sometimes tearing apart. Where they tear apart, oceans opened. Plate motion is so slow that we cannot perceive it; earthquakes and volcanic eruptions being the most prominent among these. There are three kinds of boundaries: these exist.
Where plates drift apart;
Where plates collide; and
Where plates pass each other sideways.
Where the plates drift apart, molten rock wells up from inside the earth, filling the space between them and forming new crust. The up-welling rock builds a ridge, and when molten rock wells up in the ridge, hardened rock is torn apart, thus causing earthquakes. Sometimes, the under-sea volcanoes grow/so tall that they become islands.
The mid-Atlantic ridge marks the place where several hundred million years ago, the Americas were joined to Eurasia and Africa. At that time, according to the earth scientists, all the earth’s landmasses formed one giant continent, which was surrounded by one big ocean. About 200 million years ago. A big crack open under the super continent and tore it in two later on other riffs tore the two continents into smaller pieces these smaller pieces became the continents we know today as the continents are still drifting apart the Atlantic Ocean is still growing wider in the Pacific Ocean narrower.
When two plates collide, one of them slides beneath the other, into the mantle as other plates advance over them. This also explains why earthquakes occur and volcanoes erupt frequently around the rim of the pacific. The sliding of plates puts a rock under great strain and when it snaps, Earthquakes take place. As blizzards slide into the mantle, rock melts, magma wells up and thus volcanoes erupt. Sometimes, tow plates collide in mid-ocean. One slides under the other, forming an ocean chain of islands that are built up. They are made of lava that erupts from volcanoes. The island of Japan and Indonesia were formed this way.
Sometimes two continents carrying plates collide. They smash the landmasses together and crumple the crust into mountains. The plates carrying Pakistan and India, for example, is in collision whit the one carrying china. The crumbling and buckling of the crust have formed the Himalaya mountains; Earthquakes resulting from his process are frequent occurrence along the collision boundary and beyond in China and Pakistan.
In the third kind of boundary, two players move past each other sideways. The movement is not smooth because as the giant slabs of rock move past each other, their edges grind together, snag and lock. This strain builds up until the snagged rock snaps, and an earthquake takes place. The San Andrea’s Faults of the U.S.A is part of such a boundary.
It looks strange that great plates drift, Collide and pass sideways. Yet this is how the earth scientists account for the big earthquakes and volcanic eruptions in different regions of the world.
Earth’s Changing Face is republished here.