编辑点评: GRE阅读的方法相信大家已经积累了很多了,本文就为大家提供一些GRE阅读的材料,大家来练一练,把平时学到的东西运用到实际中,也多多积累词汇和句子,提高自己的阅读能力。
每天做一些标准的GRE阅读练习,有助于大家在GRE考试的复习过程中不断地进行练习和总结。希望大家在进行GRE阅读练习时,充分运用平时所积累的知识,这样才能有效果。
Geologists have long known that the Earth s mantle is heterogeneous, but its spatial arrangement remains unresolved is the mantle essentially layered or irregularly heterogeneous? The best evidence for the layered mantle thesis is the well-established fact that volcanic rocks found on oceanic islands, islands believed to result from mantle plumes arising from the lower mantle, are composed of material fundamentally different from that of the midocean ridge system, whose source, most geologists contend, is the upper mantle.
Some geologists, however, on the basis of observations concerning mantle xenoliths, argue that the mantle is not layered, but that heterogeneity is created by fluids rich in incompatible elements percolating upward and transforming portions of the upper mantle irregularly, according to the vagaries of the fluids pathways. We believe, perhaps unimaginatively, that this debate can be resolved through further study, and that the underexplored midocean ridge system is the key.
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