新托福考试阅读练习资料：地球曾是个雪球？.pdf

智 课 网 托 福 备 考 资 料新托福考试阅读练习资料：地球曾是个雪球？如果地球气温逐渐降低，地球可能会成为一个雪球，就像700万年前那样?今天的新托福考试阅读练习资料就要与我们讨论这个话题。An impression of a frozen Earth shrouded in snow and ice.Basic organisms may have survived in pockets of open water,according to new researchLife may have survived a cataclysmic global freeze some 700million years ago in pockets of open ocean.Researchers claim to have found evidence in Australia thatturbulent seas still raged during the period,wheremicroorganisms may have clung on for life.Conditions on what is dubbed Snowball Earth were soharsh that most life is thought to have perished.Details are published in the journal Geology.The researchers in Britain and Australia claim to have founddeposits in the remote Flinders Ranges in South Australia whichbear the unmistakable mark of turbulent oceans.They say the sediments date to the Sturtian glaciation some700 million years ago,one of two great ice ages of theCryogenian period associated with the Snowball Earthhypothesis.These sediments,they say,prove pockets of open oceanwaters must have existed during the period,perhaps supportingmicroscopic life.The snowball earth hypothesis suggests the land and oceansof our planet were thrown into a deep freeze,the like of whichhas never been seen before or since.For the first time,we have very clear evidence that stormswere affecting the sea floor,said Dr Dan Le Heron of RoyalHolloway,University of London,who lead the research.Thatmeans we have to have pockets or oases within this SnowballEarth that are free of ice.We see a very particular type of feature in sedimentaryrocks called hummocky cross-bedding.These features can onlyform where storm waves sweep up sand from the ocean floor,slosh it back and forth and create a bed of sandstone.These ocean pockets could explain how somemicroorganisms survived the period and went on to flourish anddiversify during the later Cambrian period.This could be one of the ideal places for early organisms tostart thriving and for evolution to really start kicking in.Slushball EarthThe Snowball Earth hypothesis is just that-a hypothesis-and while most agree on the evidence for a deep freeze,argument remains over the causes and the extent to which theentire globe froze during the Sturtian and Marinoan glaciations.Some wonder how any life could have survived such a deepfreeze.Professor Doug Benn of the University Centre in Svalbard,who admits to being more a Slushball Earth or Softball Earththeorist said:The paper supports the idea that the Earth was notcompletely frozen throughout one of the extreme glaciations inthe late Precambrian.The Snowball model was ground-breaking in its time,butnow it has to be replaced by a more dynamic-and even moreinteresting-picture of how the Earth functioned in the distantpast,he said.