杏吧原创

QUESTIONS of origin have long been a source of fascination for mankind. How did the universe come into being? Where did we come from? Which came first, chicken or egg?

The earth sciences encompass a particular richness of such questions. It is in the nature of origins that the traces left behind are often obscured by later events. We require modern specialist techniques and knowledge to unravel their details. At the same time, the uniformitarian principle 鈥� the idea that the physical processes that shaped the Earth have always been the same 鈥� is more problematic in the very deep geological past when the world was young.

The earliest epoch of rock formation on Earth is known as the Hadean: it is the 鈥渃overed era鈥�. Together with the early Archaean, this period saw the formation of the earliest rocks and minerals, the oceans and atmosphere. It was the time when convection in the planet鈥檚 mantle layer started to drive the plate tectonics that, within the solar system, appears to be unique to the Earth. And it harboured perhaps the most significant origin of all, that of terrestrial life.

In The Early Earth, international experts present their recent findings on many of these matters: the origins of the ancient crust and lithospheric mantle; the earliest recorded subduction zones; and the formation of the atmosphere and its modification by extraterrestrial and biological interventions during the first 2 billion years of Earth鈥檚 history. All this set the scene for the following 2.5 billion years, the realm of traditional geology, which saw steady geological and biological evolution. The Early Earth requires a good background in geology and would be ideal reading for graduate students or researchers interested in our understanding of the early Archaean.

Wenk and Bulakh鈥檚 Minerals is both authoritative and accessible, providing a thorough grounding in many aspects of modern mineralogy in a first-rate text. It is unfortunately let down by the last two chapters, which deal with the origin and internal structure of the Earth.