你真的会读托福阅读吗?
发布时间:2017-06-02 14:16:15 已帮助:210人 来源:武汉飞渡教育
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" (elements tending toward liquid rather than solid state) 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.
以上就是
武汉飞渡教育
小编为您整理你真的会读托福阅读吗?的全部内容,更多精彩请 在线咨询
也可以拨打咨询电话:
400-888-4851
让在线老师为你详细解答