Planet Earth: A Beginner's Guide (Beginner's Guides)
John Gribbin
Language: English
Pages: 192
ISBN: 1851688285
Format: PDF / Kindle (mobi) / ePub
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remelted. The dense, metallic core of the incoming object would have sunk through this molten outer layer and been absorbed into the core of the young Earth, while lighter material from the incoming object and from the Earth’s original surface would have been splattered out into space. About ten times the present mass of the moon would have been ejected in this way. Most of it escaped entirely into independent orbits around the sun, but some was captured in a ring of material around the Earth. As
the plume collapsed back into the interior of the Earth, and the crust around the centre of the dome collapsed downwards, creating a series of deep rifts in the Earth’s surface. One of these rifts in the side of the dome became the Great Rift Valley; nearby, another rift dropped below sea level, forming the Red Sea as water rushed in to the resulting crack. At the same time, molten material continued to well up into the crack, which is about 1800 kilometres (1100 miles) long, pushing the two
wood turned to charcoal, iron bars bent into fantastic shapes, and all glass melted. One wrote of a ‘desert of desolation, encompassed by appalling silence ... a world beyond the grave’. A French scientist was horrified by the ‘pulverized, formless, putrid things which are all that is left of St Pierre’. The damage had mostly been done by hot gas; the flow left behind only a thin layer of white ash, which covered the ruined city. In the space of a few seconds, the town and its thirty thousand or
harder to come by in very old strata. There are very few fossils at all to be found more than about 600 million years old, in the great stretch of geological time known as the Precambrian, which spans roughly eighty-five per cent of Earth history. This is because it was only in the Cambrian period, beginning about 550 million years ago, that creatures with shells and bones evolved. Shells and bones make good fossils; the soft-bodied life forms of the Precambrian did not. The very fact that so
of terrestrial time, the framework within which the present features of the Earth, including its suitability as a home for life, have evolved. We cannot tell that whole story here. But we will tell you how the forces that shaped the Earth are still active today, causing earthquakes and volcanoes, ripping the Earth’s crust apart as ocean basins grow, and pushing landmasses around in a changing pattern that produces collisions between continents in which great mountain ranges grow. Both geological
