Science has come a long way in uncovering some of the mysteries of Earth. But we don’t know where and how life emerged on the planet. “For more than two centuries,” writes Ferris Jabr, “Western science has regarded the origin of life as something that happened on or in Earth, as if the planet were simply the setting for a singular phenomenon, the manger that housed a miracle.” This thought-provoking read explores the idea that the living creatures on Earth—humans, animals, plants, microorganisms—aren’t just products of evolutionary processes over millions of years, but rather participants in their own evolution. In other words, we are Earth. Jabr recounts his descent deep into the Earth’s crust, witnessing the very hot, very active interior of the planet—a subterranean environment teeming with ancient intraterrestrial microbes that may well have helped form the continents and laid the foundations for terrestrial life.
The history of life on Earth is the history of life’s remaking Earth. Nearly two and a half billion years ago, photosynthetic ocean microbes called cyanobacteria permanently altered the planet, suffusing the atmosphere with oxygen, imbuing the sky with its familiar blue hue and initiating the formation of the ozone layer, which protected new waves of life from harmful exposure to ultraviolet radiation. Today plants and other photosynthetic organisms appear to help maintain a level of atmospheric oxygen high enough to support complex life but not so high that Earth would erupt in flames at the slightest spark. Marine plankton drive chemical cycles on which all other life depends and emit gases that increase cloud cover, modifying global climate. Kelp forests, coral reefs and shellfish store huge amounts of carbon, buffer ocean acidity, improve water quality and defend shorelines from severe weather. Animals as diverse as elephants, prairie dogs and termites continually reconstruct the planet’s crust, facilitating the flow of water, air and nutrients and improving the prospects of millions of species. And micro-organisms, like those I observed deep within Earth’s crust, are now thought to be important players in many geological processes.
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