The Life and Death of Planet Earth by Peter Ward and Donald Brownlee, Times Books/Henry Holt, $25, ISBN 1591020638
TWO phrases spring to mind when you read this book: 鈥測ou never had it so good鈥� and 鈥渢he end of the world is nigh鈥�. These pessimistic and doom-provoking thoughts echo continuously throughout this riveting read.
Authors Peter Ward and Donald Brownlee are both professors at the University of Washington in Seattle. Ward, a palaeontologist, uses the fossil record to explain how Earth got to its present state. Brownlee, an astronomer, gazes into the celestial crystal ball and foretells how our planet is going to change. Neither has good news.
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Palaeontological evidence shows that life began as soon as the physical and chemical conditions allowed. Slimy, single-celled organisms originated about 3800 million years ago, 800 million years after Earth formed. A mere 500 million years ago animals appeared, and quickly dominated the planet. At that time the continents were conveniently strung out along the equator. But continents move, oceans form and then disappear, and volcanic activity varies, altering the global climate again and again. Added to this are the effects of asteroid and comet impacts. These have combined to produce about five mass extinctions in this brief 鈥渁nimal鈥� time period.
Then there鈥檚 the ice. Steady periodic variations in the shape of Earth鈥檚 orbit, tilt and direction of its spin axis alter climate, sea level and glacial coverage. Human civilisation today is lucky to occupy a brief interglacial period.
In astronomical terms we must worry about the Sun. Our central star is now 30 per cent brighter than it was when Earth formed. Gradually and inexorably it is getting warmer. Wind, rain and erosion are all increasing. For animals, it鈥檚 downhill all the way from now on. When the average global temperature reaches 38 掳C, the decline in animal life becomes precipitous.
In 500 million years the oceans are gone, the lithospheric plates have ceased moving, mountains are no longer formed and life is all but extinguished. No one is left to witness the Sun expanding into a red giant and consuming our inner planetary neighbours Mercury and Venus; no one is around to worry about the Milky Way鈥檚 collision with the Andromeda Galaxy in 3000 million years. Our world began hot and sterile: massive asteroid bombardment and high rock radioactivity saw to that. It will end hot and sterile too. Solar evolution is unstoppable. Planets need to be close to a star for life to develop, but being that close means that life will inevitably be destroyed.
The message of this book is that advanced planetary life is difficult to form, is fragile when formed, and is anything but permanent. But The Life and Death of Planet Earth is not all gloom. It is a gripping tale of modern scientific investigation that underlines the insights produced when scientific disciplines cooperate. Ward and Brownlee show that astrobiology 鈥� the study of the origin and evolution of life in differing planetary environments 鈥� should join forces with palaeontology, astronomy, geology and geophysics.
The authors stress relationships between the life forms on Earth and the state, positions and sizes of our oceans and continents. Into this fascinating story they weave the steady variability of astronomical characteristics such as the energy output of the Sun, the lunar position, and the Earth鈥檚 orbit, atmosphere and bombardment history. They also point out the relevance of all this to the existence of intelligent life elsewhere in the Universe.
This is a modern subject on the move. Such an excellent introduction will do much to encourage new scientists to take up the baton and, I hope, refine some of the concepts.
