How to survive a killer asteroid

How to survive a killer asteroid
How to survive a killer asteroid. Picture: Elena Lacey/Wired

The impact that wiped out the dinosaurs would probably have killed you too — unless you were in the exact right place and had made the exact right plans.

Let’s say for a moment you want to camp alongside the dinosaurs. But not just any dinosaurs. You want to camp alongside the most famous. The most fearsome. So let’s say you spin the dials on a time machine to 66.5 million years ago and you travel back to the late Cretaceous period.

There’s the tyrannosaurus hunting the triceratops. There’s the alamosaurus, one of the largest creatures to ever walk the earth. There’s the tank-like ankylosaurus crushing opponents with its wrecking-ball tail. And just as you settle down on one particular evening, there’s a brand-new star in the northern hemisphere sky.

The star won’t flash, flare up, or blaze across the horizon. It will appear as stationary and as twinkly as all the others. But look again a few hours later and you might think this new star seems a little brighter. Look again the next night and it will be the brightest star in the sky. Then it will outshine the planets. Then the moon. Then the sun. Then it will streak through the atmosphere, strike the earth, and unleash 100 million times more energy than the largest thermonuclear device ever detonated. You’ll want to pack up your tent before then. And maybe move to the other side of the planet.

The day the Chicxulub asteroid slammed into what is now a small town on Mexico’s Yucatán peninsula that bears its name is the most consequential moment in the history of life on our planet. In a prehistoric nanosecond, the reign of the dinosaurs ended and the rise of mammals began. Not only did the impact exterminate every dinosaur save for a few ground-nesting birds, it killed every land mammal larger than a raccoon. In a flash, Earth began one of the most apocalyptical periods in its history. Could you survive it? Maybe.

If you make camp on the right continent, in the right environment, and you seek out the right kind of shelter, at the right altitudes, at the right times, you might stand a chance, says Charles Bardeen, a climate scientist at the National Center for Atmospheric Research who recently modeled the asteroid’s fallout for the Proceedings of National Academy of Sciences. Of course, even if you are on the opposite side of the world at the time of impact — which is the only way you can hope to make it out alive — he recommends you act quickly. As soon as you hear its sonic boom (don’t worry — you’ll be able to hear it from the other side of the world), get yourself to high ground and find underground shelter. Immediately.

How to survive a killer asteroid
The Chicxulub blast. Picture: Cody Cassidy/Kevin Plottner

You might think this sounds a bit alarmist. If you’re on the opposite side of the world — which you should be — why do you need to duck and cover from a city-sized rock landing 10,000 miles away?

But you wouldn’t be the first to make the mistake of underestimating an asteroid. The cataclysmic risk posed by asteroids wasn’t well understood until World War I. Before then, most astronomers operated under the blissful naivete that massive impacts like Chicxulub were simply not possible.

When Galileo trained his telescope on the moon in 1609 and discovered perfectly circular craters dominating its topography, astronomers began to wonder how they formed. A few astronomers, like Franz von Gruithuisen, an early-19th-century German, proposed asteroid impacts as the cause. But most rejected this theory based upon one simple, supremely confounding fact: The moon’s craters are almost perfect circles.

And, as anyone who has thrown a rock into dirt can tell you, that isn’t what an impact scar should look like. Instead, the mark will be oblong, oval, and messy. (Gruithuisen probably didn’t help his cause by also claiming to have seen cows grazing upon moon grass in these craters.) Further misleading any theorists, astronomers could make out little mountains in the center of each depression. Thus, for 300 years the majority of astronomers and physicists believed that (1) cows did not graze upon moon meadows, and (2) lunar volcanoes, rather than meteors, had pocked its face.

Then, in the early 1900s, astronomers like Russia’s Nikolai Morozov* began observing newly developed high explosives and made a rather startling discovery: Large explosions differ from thrown rocks in a number of ways, but most ominously — at least for our species’ continued existence — they leave circular craters regardless of their angle of impact. As Morozov wrote in 1909 after conducting a series of experiments, asteroid impacts would “discard the surrounding dust in all directions regardless of their translational motion in the same way as artillery grenades do when falling on the loose earth.”

Before Morozov’s discovery, astronomers were aware that asteroids could be devastating. “The fall of a bolide of even ten miles in diameter … would have been sufficient to destroy organic life of the earth,” wrote Nathan Shaler, dean of Harvard’s Lawrence Scientific School and proponent of the volcano theory, in 1903. But most believed this was an entirely theoretical exercise, partly because, as Shaler noted in his defense of the lunar volcanism theory, the very existence of humanity proved this sort of impact could not have occurred.

Morozov’s calculations changed that. Once you know the true origins of the scars on the moon, you don’t have to be an astronomer — or even own a telescope — to arrive at the sobering conclusion that asteroids carry apocalyptic potential and that their impacts are inevitable.

Shaler was, in a way, presciently incorrect. An asteroid of nearly the size he described did impact Earth and did wipe out the planet’s dominant species. Only rather than wiping out humans it cleared the evolutionary path for a shrew-sized placental mammal to eventually crawl, walk, and consider a camping trip to the apocalypse.

You might think the survival of your shrewlike ancestor proves that a larger-brained mammal like yourself would stand a reasonable chance. Unfortunately, the shrew had a number of apocalypse-friendly adaptations humans have since lost. The shrew could survive on insects, burrow away from the heat, and had fur to warm itself during the freezing decade that followed. You could replicate some of the shrew’s survival strategies. You could burrow and expand your diet. But evolution has robbed you of others, and your opposable thumbs might not be enough to save you when that twinkling star enters Earth’s atmosphere at 12.5 miles per second.

At impacts of that speed, Earth’s atmosphere behaves like water. Smaller rocks — called meteors — hit the atmosphere like pebbles into a pond; they decelerate rapidly at high altitudes, either burning away in their friction with the air or decelerating to their low-altitude terminal velocity of 164 mph. But the mountain-sized Chicxulub asteroid hits our atmosphere like a boulder into a puddle. It maintains its velocity until impact, plunging through the entire 60 miles of atmosphere in fewer than three seconds. The asteroid screeches over Central America, emitting a sonic boom that reverberates across the continents.

It falls so quickly that the air itself cannot escape. Under intense compression, the air heats thousands of degrees almost instantly. Before the asteroid even arrives, compressed and superheated air vaporizes much of the shallow sea that covers the Yucatán in the late Cretaceous. Milliseconds later, the rock plunges through what’s left and slams into bedrock at more than 10 miles per second. In that instant, a few near-simultaneous processes occur.

First, the impacting meteor applies so much pressure to the soil and rock that they neither shatter nor crumble, but instead flow like fluids. This radical effect actually makes it easier to visualize the formation of the crater, because the undulations of the earth almost exactly replicate the double-splash of a cannonballer in a backyard pool. The initial splash in all directions is followed by a delayed, vertical sploosh when the cavity created by the impactor rebounds to the surface.

In a swimming pool, this entire process occurs in a few seconds. In Chicxulub, it takes around 10 minutes, but the difference is a function of scale, not speed. The initial wall of earth gouged outward at the moment of impact is more than 20 miles high; the transitory cavity nearly breaches Earth’s mantle, and when the cavity rebounds to form the delayed “vertical sploosh,” the earth rises at over 1,000 mph to heights taller than Mount Everest. Within minutes this mountain almost entirely collapses in a series of secondary explosions, but it leaves behind a smaller mound — called a crater’s “peak ring,” it is the formation that so confused those early moon gazers.

At the very same moment the asteroid first strikes the Yucatán and applies its pressure to the bedrock, it also converts the kinetic energy of a 7.5 billion ton rock traveling 10 miles per second into heat. In an instant.

Why a rock hitting another rock results in heat isn’t particularly intuitive, because we don’t generally deal with kinetic energy on this scale. But thermodynamically, heat is simply the movement of molecules. The jigglier the molecules, the hotter the temperature. You can jiggle the molecules in an object by any number of means, but physically hitting them works, which is why a hammer heats up after you hit a nail. But whereas a hammer swing delivers approximately 0.0001 kilojoules of energy, the Chicxulub impactor delivers approximately 1,300,000,000,000,000,000,000,000. The kinetic energy transferred by the asteroid to the rock, soil, and air jiggles the molecules to temperatures that exceed the surface of the sun.

The heat rips away electrons from atoms, ionizing the air into an expanding fireball of plasma turbocharged with vaporized rock, which is all blasted out at hypersonic speeds. The heated, rapidly expanding air and near-instantaneous conversion of earth to gas combines with the impact shockwave of the meteor itself to form a massive blast wave of pressure expanding outward at more than 1,000 mph.

“The only comparable event is a shallow-depth thermonuclear explosion. Though, depending on their size, the energy associated with meteoric impacts can be much greater,” says Elizabeth Silber, a planetary scientist at Western University who wrote an article titled “Physics of Meteor-Generated Shockwaves in Earth’s Atmosphere,” in Advances in Space Research. In this case, 100 million times greater. If this asteroid hit in the same spot today, the blast wave would kill you in Texas, deafen you in New York, and blow out window panes in Buenos Aires.

The rock rings Earth like a bell. Waves in Earth’s crust radiate away from the impact zone at 2.5 miles per second. These waves then trigger fault-slipping earthquakes across the continents. If you’re on the other side of the world, you can expect to feel the ground-shaking effects 30 minutes after impact. Stay away from the banks of any large body of water, where earthquakes may trigger tsunami-like seiche waves even in fjords or lakes. Even more importantly, stay off the beach.

The impact triggers tsunamis — plural — as high as skyscrapers. The first of them hit gulf coastlines within the hour. Waves ranging from 600 feet to perhaps as tall as a 1,000 feet smash into what is now Mexico and the southern United States and flood tens of miles inland.The waves temporarily reverse the flow of rivers, rushing up river beds like 30-foot tidal bores.

How to survive a killer asteroid
How you would die. Picture: Cody Cassidy/Kevin Plottner

Tsunamis wrap up the eastern seaboard, smash into the eastern coast of the United States, and, six hours after impact, crest as 600-foot-high walls of water in Europe, Africa, and the Mediterranean coasts. Within 15 hours of impact, waves arrive on every coastline on the planet. Depending on local topography, the ocean sweeps away anything in its path and sucks it back to the sea when the waters finally retreat.

These tsunamis deeply complicate your survival strategy, because proximity to the coastline is otherwise a good idea in super-large asteroid strikes. The ocean serves as Earth’s great insulator, moderating the severe temperature swings that massive asteroids induce. In the case of Chicxulub, the swing starts with heat.

When the big rock strikes, its splash constitutes 25 trillion tons of earth that it launches on ballistic trajectories, some at speeds that exceed Earth’s escape velocity. These rocks exit Earth’s gravitational pull to either orbit the sun or embed themselves on other moons or planets as meteors themselves. But the majority of ejected debris returns back to Earth within the hour. These glass-like chunks, called tektites — some as large as school buses, but most the size of marbles — pelt the earth at speeds ranging from 100 to 200 mph in lethal quantities. Regardless of where you are on Earth, you’ll need to find protection from this fiery hailstorm.

Bardeen suggests a cave.

But these glass bullets don’t need to hit you to kill you. As they fall, their friction with the atmosphere collectively emits enough thermal radiation to set fires across the world. By some estimates, the combined heat of the returning embers is the equivalent of a home oven set to broil. Most of the world’s trees burn, which is perhaps why the only bird species that survive the impact are those that nest on the ground. Of the few larger land animals to avoid extinction, nearly all have some means of escaping the heat. They either could burrow — like small mammals, snakes, and lizards — or escape into water, like crocodiles or turtles. This suggests that even if you’re on the other side of the world, you’ll need to find protection from the initial heat blast.

Bardeen suggests a deep cave.

In a final piece of terrible luck for the dinosaurs (and you), Chicxulub happens to strike an area rich in oil and sulfur. The impact ejects 100 billion tons of vaporized sulfur and 10,000 Lake Superiors worth of water into the atmosphere, which then condenses into massive storm clouds and falls back as torrents of acid rain. In the higher latitudes, continental-wide snow storms deposit tens of feet per day. But the global inundation doesn’t last long, because in addition to water, Chicxulub vaporizes and forcefully ejects 150 football stadiums worth of oil in the Yucatán bedrock. This oil then condenses in the stratosphere as a black sooty layer, covering Earth like a coat of black paint.

Unlike the sulfur and wildfire smokethe carbon circulates high above the cloud layer so it doesn’t rain back down. And that’s the problem. The soot layer persists, reducing the amount of sunlight that reaches Earth’s surface by 90 percent for at least three years, so the initial ovenlike heat brought on by the returning tektites is followed by a deep, prolonged freeze.

Global temperatures drop by an average of almost 50 degrees. The only places on Earth to avoid frost are tropical islands like Madagascar, India (at the time an island), and Indonesia. Not only are these places where you have the best chance of finding plants and the animals that eat them, but according to climate models these tropical islands are some of the few places on Earth that continue to receive fresh water.

In the global chill, evaporation almost ceases, which drops rainfall by 80 percent. Nearly every spot on earth outside of these tropical islands dries into a desert. These islands might be an apocalyptical oasis, but they are no paradise. Skip the sunscreen, and pack extra food. These islands receive barely 10 percent of their normal sunlight and barely receive enough rainfall to stay above desertification.

How to survive a killer asteroid
Environmental impact after a killer asteroid impact. Picture: Cody Cassidy/Kevin Plottner

In this cold, dim environment, most food chains collapse. But not all. Fossil evidence suggests freshwater ecosystems fared among the best, so proximity to a river or estuary would be your best bet in terms of foraging for food. There, you may find turtles, crocodiles, and some fish to eat. Sediment-living animals, such as clams, snails, and small crustaceans, also do quite well in the post-impact environment. Still, Bardeen warns against any trips by the ill-prepared. “To survive, you would have to bring something to keep you warm, and at least six years of food supply to stand any chance,” he says.

But if you cannot be dissuaded, then at least find a mountainous, tropical island like what is now Indonesia. There you’ll find a tolerable temperature, at least a little rain, and a deep cave. You’ll find shelter from the rain of tektites, the searing heat, and perhaps something to eat in the rivers and lakes. Just spare any shrewlike creatures you may find in your desperate search for food. It’s unclear how many survived the Chicxulub, so eating the wrong one could result in some rather unintended consequences for the rest of humanity.

About the Author:
Cody Cassidy is the co-author of the popular science book And Then You’re Dead, which was translated into more than ten languages, and a former bookstore clerk in Buenos Aires. His new book is Who Ate the First Oyster? [Wired]

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