小马托福阅读tpo27文本解析下载二

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小马托福阅读TPO27文本解析下载二
小马托福阅读TPO27 文本解析下载二。下面为大家整理了小马过河官方版托福阅读TPO，主要包括了第27
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托福阅读TPO27 解析
TPO27-1-2 原文：The Formation of Volcanic Islands

Earth’s surface is not made up of a single sheet of rock that forms a crust but rather a number
of “tectonic plates” that fit closely, like the pieces of a giant jigsaw puzzle. Some plates
carry islands or continents others form the seafloor. All are slowly moving because the plates
float on a denser semi-liquid mantle, the layer between the crust and Earth’s core. The plates
have edges that are spreading ridges (where two plates are moving apart and new seafloor is
being created), subduction zones (where two plates collide and one plunges beneath the other),
or transform faults (where two plates neither converge nor diverge but merely move past one
another). It is at the boundaries between plates that most of Earth’s volcanism and earthquake
activity occur.

Generally speaking, the interiors of plates are geologically uneventful. However, there are
exceptions. A glance at a map of the Pacific Ocean reveals that there are many islands far out
at sea that are actually volcanoes----many no longer active, some overgrown with coral----that
originated from activity at points in the interior of the Pacific Plate that forms the Pacific
seafloor.

How can volcanic activity occur so far from a plate boundary? The Hawaiian Islands provide a
very instructive answer. Like many other island groups, they form a chain. The Hawaiian Islands
Chain extends northwest from the island of Hawaii. In the 1840s American geologist James Daly
observed that the different Hawaii islands seem to share a similar geologic evolution but are
progressively more eroded, and therefore probable older, toward the northwest. Then in 1963,
in the early days of the development of the theory of plate tectonics. Canadian geophysicist
Tuzo Wilson realized that this age progression could result if the islands were formed on a surface plate moving over a fixed volcanic source in the interior. Wilson suggested that the
long chain of volcanoes stretching northwest from Hawaii is simply the surface expression of
a long-lived volcanic source located beneath the tectonic plate in the mantle. Today’s most