雅思阅读:Amazon River shaped by see-saw tilt of continent
SOUTH AMERICAS AMAZON RIVER Basin was a vast wetland for millions of years. That was until tectonic processes deep in the Earth transformed it into the worlds largest drainage system, new research suggests.
Geoscientists from the University of Sydney and the California Institute of Technology believe a process called continental tilting, which began about 30 million years ago and continued for about 16 million years, tipped South America like a see-saw and drained its wetlands.
The event, funnelled water over 6400 km east to the Atlantic Ocean in what the team describes as the worlds largest water slide. What were describing involves the whole continent, lead author Grace Shephard told Australian Geographic. This tilting led to the formation of the Amazon River as we know it today.
Sinking slabs
The team used computer simulation to demonstrate the continents movement across a subduction zone, where slabs of the Earths crust sink into the softened rocks of the mantle, causing it to tilt. With time, as South America moved further west of these sinking slabs, the northeast subsided by up to 400 m, while the west was uplifted.
We had a hunch that the ultimate forces leading to this fundamental shift in continental topography had something to do with the westward motion of South America over dense, sinking mantle rocks while the Atlantic Ocean opened up, explains Grace.
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