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.
The creation of the Amazon River had previously been attributed to the growth of the Andes Mountains damming the westward movement of water from the wetland and creating a smaller sloped effect. Grace says the teams discovery is important because it shows the way in which the interaction between the Earths crust and the mantle underneath can fundamentally reshape the topography and ecosystems of continents.
Wobble board effects
While demonstrated most spectacularly in the Amazon Basin, continental tilting is known to have occurred elsewhere, including in our own backyard.
The idea of sinking slabs is shown to have occurred in North America and there are applications to Australia, says Grace, where eastern parts of the country are believed to have swung up and down like a giant wobble board. Grace says it is possible that similar tilting has created and destroyed other large river systems over time, such as a Triassic-era movement perhaps responsible for forming Sydneys bedrock, the Hawkesbury sandstone.
Geophysicist Louis Moresi from Melbournes Monash University, who was not involved in the research, says the teams work is fascinating and demonstrates the way in which continental tilting can influence river systems over millions of years.
An additional 400 m of topography might not seem much in contrast with the height of the Andes, but it is a very broad-scale tilting of the continent which drainage and erosion cannot resist, says Louis.
攻克2015年职称英语完形填空的最佳解题思路
2015年职称英语备考经验:菜鸟成才之路
新手必看:2015职称英语考试复习需要注意事项
2015年职称英语考试通关重要法宝:温故知新
2015年职称英语完形填空命题方向,你不得不看!
备考经验:2015年职称英语考试内容
2015年职称英语考试技巧—“小”技巧也可争高分
抓住一切零散时间备考2015年职称英语考试
职称英语考试如何快速复习通过2015年考试
初春如何备考2015职称英语考试?
2015年职称英语阅读“五不要”
2015年职称英语考试备考实用技巧五则
2015年职称英语考生须知:选词典及快速查词技巧
有效利用历年真题备考2015年职称英语
都教授说职称英语:2015年复习指导策略
2015职称英语通关经验:温故知新
2015年职称英语考试扩大阅读范围的方法
职称英语考试须知的阅读判断做题技巧
2015年职称英语过关法宝:做好3点 建立信心!
2015年职称英语词汇选项做题小技巧
2015年职称英语考试阅读判断备考方法
2015年职称英语迅速攻克阅读理解的四大妙招
2015年职称英语考试答题顺序及答题时间控制
2015年职称英语词汇选项必杀技
如何利用好自己的时间,轻松备考职称英语?
2015年职称英语备考经验:抓住规律做好阅读判断
影响职称英语考试阅读理解能力的三大因素
2015年职称英语10大疯狂单词记忆法
2015年职称英语考试技巧:如何寻找主旨句
牛人分享:2015年职称英语考场答题必看21点
| 不限 |
| 英语教案 |
| 英语课件 |
| 英语试题 |
| 不限 |
| 不限 |
| 上册 |
| 下册 |
| 不限 |