The continents are in constant motion: Tectonic plates crash together and break apart, creating new crust while old crust is pulled below the surface. The process shrinks and widens oceans, uplifts mountain ranges, and rearranges landmasses. In about 250 million years a new supercontinent, Pangaea Proxima, will form. Fifty million years from now, Australia will be in collision with southeast Asia to a much larger degree," he says. Africa will also be pushing right up against southern Europe, while the Atlantic will be a far wider ocean than it is today. The idea that the continents moved around dates back centuries, but the first time anyone produced any serious evidence in favor of the idea was 100 years ago. That someone was German geophysicist Alfred Wegener.
For many geologists, continental drift was a crackpot idea with little hard evidence
He noticed remarkable similarities between the fossilized plants and animals found on continents that were separated by vast oceans. This suggested to him that those continents were connected when those now fossilized species were alive.
What's more, when Wegener looked at his maps, he could clearly see that South America and Africa were like two giant puzzle pieces – they fit together. Could that really just be coincidence, or were they connected millions of years ago, only to drift apart?
That was the essence of Wegener's theory: continental drift. But few people liked it.
In fact, for many geologists, continental drift was a crackpot idea with little hard evidence. How exactly could massive continents move?
Wegener could not provide a satisfactory explanation. He died in 1930. But his idea lived on, and 20 years later, his vindication would begin.
South America and Africa were like two giant puzzle pieces – they fit together
The crucial secrets that would unlock the truth of his theory were not to be found on those moving continents. They were all hidden under the sea.
Marie Tharp was one of the first people to realize that mountain ranges and huge valleys were not just features found on land, but under the oceans as well. In the early 1950s Tharp helped to map a gigantic submarine mountain range, thousands of kilometers long but only a few kilometers wide, zigzagging right down the middle of the Atlantic Ocean.
Similar ranges lie beneath the waves of other oceans. They have since been named "mid-ocean ridges" – and their discovery helped turn the tide of thought on how the Earth's surface had formed.
Harry Hess, an American geologist and submarine commander in World War Two, recognized the potential significance of the mid-ocean ridges.
This sideways movement of rock... could ultimately explain why the continents themselves moved
During the war, Hess had used sonar to map some areas of the ocean floor in detail. He had found it to be far from the flat, featureless landscape most geologists had assumed it to be.
The discovery of mid-ocean ridges fit with an idea he was developing – namely that the ocean floor is constantly, but very slowly, renewing itself. He suggested that hot magma welled up along the mid-ocean ridges and cooled into rock. Then, as more hot magma welled up at the ridge, the cool rock was pushed down the ridge flanks to make room.
This sideways movement of rock, perpendicular to the mid-ocean ridges, could ultimately explain why the continents themselves moved. They were being pushed around by the upwelling of magma along the mid-ocean ridges.
His theory became known as "seafloor spreading". But still, other geologists were skeptical. Other features under the sea were providing more clues, though, and gradually turning the tide of opinion in Hess's favor.

#Archeology #Future #Documentary

свернуть