The Sixth Extinction

The Start of the Anthropocene

Two hundred thousand years ago, a resourceful new species emerged in Africa. Though small in number, these humans possessed a unique ability to adapt, eventually spreading across every continent. Everywhere they settled, they transformed the landscape and triggered the disappearance of massive beasts and isolated island creatures. Today, this expansion has reached a breaking point. By burning ancient fuels and clearing forests, humans are rapidly changing the atmosphere and oceans, driving a global collapse in the variety of life. For only the sixth time in Earth's history, life faces a catastrophic mass extinction, and this time, we are the cause.

In 1949, a psychology experiment revealed a strange quirk of human perception. Students were shown playing cards, but some were doctored, like a red six of spades. At high speeds, the students didn't notice the errors, seeing only what they expected to see. It was only when the cards slowed down that they experienced a "My God!" moment of realization. This experiment highlights how scientific progress works through paradigm shifts. For centuries, naturalists tried to fit strange fossils into familiar categories, like calling mammoths "lost elephants." Eventually, the evidence for extinction became too glaring to ignore.

Modern geology is often described as long periods of boredom interrupted by moments of panic. These moments are etched into the cliffs of the Scottish Southern Uplands. At Dob’s Linn, the rock layers tell a story of a world that suddenly turned cold. On a jagged, rain-slicked outcropping, Jan Zalasiewicz points to a stripe in the stone where "bad things happened" 445 million years ago. Below this line, the shale is dark and filled with the fossils of graptolites—tiny, colonial marine animals that looked like delicate sketches. Above the line, the rock turns gray and the fossils almost entirely disappear, marking the end of the Ordovician period. Roughly eighty-five percent of marine species vanished in two deadly pulses, likely caused by a sudden glaciation.

Other extinctions were caused by the opposite problem. During the end-Permian event, the planet experienced a massive release of carbon. The oceans warmed by eighteen degrees and became so acidic that most life suffocated. The seas may have turned a "grotesque" purple, releasing poisonous gases into a pale green sky. Today, we are witnessing a new kind of "panic" driven by human activity. We have dammed major rivers, transformed half of the planet's land surface, and produced more nitrogen than all natural ecosystems combined. This new era is known as the Anthropocene, a term coined by Nobel chemist Paul Crutzen. It marks a time when human influence has become a geological force as powerful as a glacier or an asteroid. Our legacy will be a thin layer of sediment containing plastic, nuclear fallout, and the bones of relocated species.