Earth's 4.5 Billion Years as One Day: All of History Fits in the Last Second

This is Vishala Space. If Earth's whole life were squeezed into a single day, every word ever written would fit in about the last tenth of a second before midnight. Here is that day. Earth is four point five four billion years old, measured to within one percent. Squeeze that into twenty-four hours, and one second on this clock is about fifty-two thousand five hundred years. One minute is about three point two million years. One hour, about one hundred and ninety million.

Watch the gold hand. When it reaches midnight, that is now. One more thing to watch: the marks on the ring. A sharp mark is a date measured to within a fraction of a percent. A wide, soft band is an honest estimate, where scientists still disagree. Midnight. The Earth is essentially finished, but you would not want to stand on it.

It took tens of millions of years to grow, and its surface is molten rock, glowing under a young Sun that shines at only about seventy percent of today's brightness. Then, at around ten minutes past midnight on the best recent estimate, comes the biggest collision in our planet's history. In the leading model, a body about the size of Mars, called Theia, strikes the young Earth. What you see is a model, drawn as rings and particles, not a photograph. The debris spreads into a ring, and the ring pulls itself together into the Moon. The newborn Moon sits far closer than today, and the Earth spins so fast that a day lasts only a few hours. At forty-three minutes past midnight, we reach the oldest thing we can still hold: a tiny crystal of zircon from Western Australia, four point four billion years old.

It is a mineral grain, not a rock, and its chemistry hints that liquid water was already here. How can we know its age? When a zircon crystal forms, it locks in a little uranium and almost no lead. The uranium slowly turns into lead at a steady, measured rate, so the ratio of lead to uranium works like a clock that has been ticking ever since. At two forty-two in the morning comes the oldest rock we know, the Acasta Gneiss in Canada, about four billion years old. In between, the young planet was hit again and again. How heavy that early bombardment was, and exactly when, is still argued, so the clock shows it as a wide, soft band, not a sharp mark.

Genetic studies suggest that the last common ancestor of every living thing today may go back to around one forty-eight in the morning. That is an estimate from DNA, so it gets a soft band too. The first clear signs of life in the rocks come later, but still before dawn. At about five thirty-six, microbes in what is now Western Australia build layered mounds, about three and a half billion years ago. For a very long time after that, every living thing on Earth is too small to see. Then the microbes change the sky. Some of them learn to make energy from sunlight and give off oxygen.

At about nine minutes past eleven in the morning, oxygen starts to build up in the air. It does not happen in one step. For about two hundred million years the level swings up and down, and oxygen only stays for good just after noon, at about twelve sixteen. You can see that change in the rocks. Iron in the oceans rusts out in red stripes, and the ring of our clock picks up the same stripes. After noon, the clock enters a long, quiet stretch that some geologists call the boring billion. Complex cells, the kind that build plants and animals, appear by about three twenty-one in the afternoon, and then for hours not much seems to change.

Why it stayed so quiet for so long is still an open question. One leading idea is that the deep oceans still had very little oxygen. One thing is changing, though: the length of the day. The Moon's pull slows the Earth's spin, and the Moon drifts outward. At about four thirty-six in the afternoon, a day on Earth lasts about eighteen point seven hours. The Moon is still moving away today, about one and a half inches every year, measured by bouncing lasers off mirrors left on the Moon. At about thirteen minutes past eight in the evening, the whole planet freezes.

Ice spreads from the poles toward the equator, and for millions of years Earth is a white ball. It happens more than once. When the last big freeze ends, at about eight thirty-nine, life starts to grow larger. And here is the twist. For about twenty-one of these twenty-four hours, there is not a single animal we can be sure of. The first ones we are sure of appear just after nine at night, soft and flat on the sea floor. One of them, Dickinsonia, left traces of cholesterol-like molecules, a chemical hallmark of animals.

At nine minutes past nine, the Cambrian begins, five hundred and thirty-nine million years ago, and the seas fill with eyes, shells and legs. Now the continents move on our globe, from real reconstructions of Earth's surface, one map for every five million years. At about nine thirty, the first plants creep onto land. Around ten, a fish with sturdy fins and a neck, called Tiktaalik, shows animals moving toward land. At twenty to eleven comes the worst extinction of all, the Great Dying, and most species in the sea vanish. Six minutes later, at about ten forty-six, the first dinosaurs appear. They do not take over straight away.

That happens after another extinction, at about ten fifty-six. All this time, the continents gather into one giant landmass, Pangaea, and then tear apart. Then, at twenty-one minutes to midnight, an asteroid about six miles wide hits what is now Mexico's Yucatán Peninsula. This is the Chicxulub impact, sixty-six million years ago, one of the most precisely dated moments in Earth's history. Again, a model: rings on the real map of the Earth as it looked back then. Every dinosaur that cannot fly is gone. The mammals, small for the whole age of the dinosaurs, finally get their turn.

Around a quarter to midnight, India, which had been moving north for tens of millions of years, runs into Asia and starts pushing up the Himalayas. So when do we arrive? You may have heard two seconds before midnight. Or four. Or seventeen. The answer depends on who counts as us. Our branch splits from the chimpanzees' at about two minutes to midnight, around seven million years ago.

The first members of our own group, Homo, appear fifty-three seconds before midnight. Four seconds later, at forty-nine seconds to midnight, the latest run of ice ages begins, the one that is still going on today. And our species, Homo sapiens, about three hundred thousand years old, arrives roughly six seconds before midnight. Six seconds. Not the last second. Everything else you know about people comes after that. Let's open those last seconds with a time lens.

Every step along it is ten times shorter than the step before. The end of the last ice age and the first farms: about a fifth of a second before midnight. The first writing, about five thousand two hundred years ago: inside about the last tenth of a second. Every story ever written fits in here, and so does the Great Pyramid. Columbus crosses the Atlantic about one hundredth of a second before midnight. The first people walk on the Moon about one thousandth of a second before midnight. At thirty frames a second, all of written history is about three frames of this video.

And one human life of eighty years lasts about one and a half thousandths of a second. Here is the whole day again, at full speed. Molten rock at midnight, a new Moon at ten past, life before dawn, oxygen by noon, ice at eight, animals at nine, dinosaurs at ten forty-six, the asteroid at eleven thirty-nine, and us in the final seconds. Next time, we go back to ten past midnight. Something hit the young Earth and made the Moon. What really happened that day, and why is the Moon still moving away? Next: the day the Moon was born.