Robert M. Hazen’s exciting explanations of how the Earth and its geologic and biologic systems formed and changed had my head spinning with growing knowledge and dawning comprehension. About five billion years ago—several billion years after the Big Bang, which Hazen explains well enough for me to finally grasp, somewhat—an event such as a shock wave from an exploding star caused a cloud of gas and dust to collapse into a star system, our Solar System. “Like a twirling ice-skater, the big cloud rotated faster and faster as gravity pulled its wispy arms to the center. As it collapsed and spun faster, the cloud became denser and flattened into a disk with a growing central bulge—the nascent Sun.” Scientists can’t say for sure how the planets formed, but because all the planets more or less rotate in the same direction and are more or less on the same plane, Hazen explains, most scientists speculate that the planets formed from the same rotating gas and dust as the Sun, and were not objects hurtling through space captured by the Sun’s gravitational pull, as was once thought.
The Earth has gone through many drastic changes since forming. The names of the chapters in The Story of Earth illustrate this: Black Earth: The First Basalt Crust; Blue Earth, The Formation of the Oceans; Gray Earth: The First Granite Crust; Living Earth: The Origins of Life; Red Earth: Photosynthesis and the Great Oxidation Event; The “Boring” Billion: The Mineral Revolution (Surprise: these billion years were anything but boring!); White Earth: The Snowball-Hothouse Cycle; Green Earth: The Rise of the Terrestrial Biosphere. I’ve never really imagined our planet as anything other than a grey ball of rock slowly turning blue and green as life began. This book shows how that view is far from accurate.
The Moon, too, has changed over the billions of years. Did you know that it is moving away from the Earth by about 3.82 centimeters per year? Scientists know this because Apollo astronauts left mirrors on the surface of the moon in the 1960s and 70s, and scientists measure the distance very accurately by bouncing laser beams off them. If the moon is moving away from the earth at that rate, can you imagine how close the moon was to the earth 4.5 billion years ago? It would have looked gigantic. The surface of the Moon was quite different back then, too. According to Hazen, “The early Moon was a violent body of intense volcanism, quite unlike the static silvery-gray object we see now. Its surface would have appeared black, with glowing red magma-filled cracks and volcanic basins easily visible from Earth.” Hazen explains the current theory of how the Moon was formed by what he calls “The Big Thwack,” or the giant impact theory.
4.5 billion years is an unfathomably long time. In 283 pages, Hazen is able to clarify to someone like me, who never took many science classes, the current theories of how Earth and the Moon formed, how life began, how mineralogical forces influence life and how life in turn influences mineralogy, and many other fascinating phenomena. One of the more interesting sections was of the Great Oxidation Event, something I had heard about but had never understood. He writes about how he and his colleagues figured out that many of the minerals we see today—turquoise, azurite, malachite, and thousands of others—could never have occurred without the Great Oxidation Event, and thus how such minerals would never be found on a non-living astronomical body like the Moon or Mars.
If you have an interest in this planet on which we’re living, and you want to know more about how it got here, how it has changed throughout the estimated 4.5 billion years since it formed, and where it may be going, read this book. It’s fascinating.
Check the WRL catalog for The Story of Earth