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Imagine aliens land on the planet a million years from now
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and look into the geologic record.
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What will these curious searchers find of us?
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They will find what geologists, scientists, and other experts
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are increasingly calling the Anthropocene,
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or new age of mankind.
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The impacts that we humans make have become so pervasive,
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profound,
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and permanent
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that some geologists argue we merit our own epoch.
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That would be a new unit in the geologic time scale
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that stretches back more than 4.5 billion years,
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or ever since the Earth took shape.
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Modern humans may be on par with the glaciers behind various ice ages
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or the asteroid that doomed most of the dinosaurs.
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What is an epoch?
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Most simply, it's a unit of geologic time.
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There's the Pleistocene,
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an icy epoch that saw the evolution of modern humans.
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Or there's the Eocene, more than 34 million years ago,
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a hothouse time during which
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the continents drifted into their present configuration.
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Changes in climate or fossils found in the rock record
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help distinguish these epochs and help geologists tell deep time.
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So what will be the record of modern people's impact on the planet?
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It doesn't rely on the things that may seem most obvious to us today,
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like sprawling cities.
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Even New York or Shanghai may prove hard to find
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buried in the rocks a million years from now.
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But humans have put new things into the world
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that never existed on Earth before,
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like plutonium
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and plastics.
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In fact, the geologists known as stratigraphers
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who determine the geologic timescale,
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have proposed a start date for the Anthropocene around 1950.
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That's when people started blowing up nuclear bombs all around the world
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and scattering novel elements to the winds.
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Those elements will last in the rock record,
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even in our bones and teeth for millions of years.
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And in just 50 years, we've made enough plastic,
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at least 8 billion metric tons,
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to cover the whole world in a thin film.
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People's farming, fishing, and forestry will also show up as a before and after
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in any such strata
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because it's those kinds of activities
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that are causing unique species of plants and animals to die out.
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This die-off started perhaps more than 40,000 years ago
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as humanity spread out of Africa
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and reached places like Australia,
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kicking off the disappearance of big, likable, and edible animals.
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This is true of Europe and Asia, think woolly mammoth,
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as well as North and South America, too.
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For a species that has only roamed
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the planet for a few hundred thousand years,
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Homo sapiens has had a big impact on the future fossil record.
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That also means that even if people were to disappear tomorrow,
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evolution would be driven by our choices to date.
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We're making a new homogenous world of certain favored plants and animals,
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like corn and rats.
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But it's a world that's not as resilient as the one it replaces.
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As the fossil record shows,
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it's a diversity of plants and animals
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that allows unique pairings of flora and fauna
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to respond to environmental challenges, and even thrive after an apocalypse.
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That goes for people, too.
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If the microscopic plants of the ocean suffer
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as a result of too much carbon dioxide, say,
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we'll lose the source of as much as half of the oxygen we need to breathe.
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Then there's the smudge in future rocks.
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People's penchant for burning coal, oil, and natural gas
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has spread tiny bits of soot all over the planet.
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That smudge corresponds with a meteoric rise
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in the amount of carbon dioxide in the air,
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now beyond 400 parts per million,
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or higher than any other Homo sapiens has ever breathed.
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Similar soot can still be found in ancient rocks
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from volcanic fires of 66 million years ago,
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a record of the cataclysm touched off by an asteroid
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at the end of the late Cretaceous epoch.
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So odds are our soot will still be here 66 million years from now,
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easy enough to find for any aliens who care to look.
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Of course, there's an important difference between us and an asteroid.
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A space rock has no choice but to follow gravity.
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We can choose to do differently.
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And if we do, there might still be some kind of human civilization thousands
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or even millions of years from now.
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Not a bad record to hope for.