Chapter Content
Okay, so, you know, people have known for a long time that the dirt under Manson, Iowa, is, like, a little bit weird. Back in 1912, some guy digging a well for the town's water supply, he reported finding all these, like, strange rocks. And, get this, the official report described them as, uh, "melted vein rock mixed with crystalline breccia fragments" and "overturned ejecta blankets." And, like, the water was weird too, almost like rainwater, like, naturally soft water, which, like, had never been found in Iowa before.
So, yeah, the rocks were weird, the water was soft, but it wasn't until, like, forty-one years later that the University of Iowa actually sent a team to check it out. Manson, then, and now, it's just this little town in northwest Iowa, only about two thousand people. In 1953, after some experimental drilling, the university geologists, they were, like, "Yeah, this is definitely odd," but they chalked up the deformed rocks to, you know, ancient volcanic activity. Which, you know, it kind of made sense at the time, but, boy, were they wrong.
The geological trauma at Manson, see, it wasn't from something inside the Earth, but from something like, at least a hundred and sixty million kilometers away. So, way, way back in the past, when Manson was on the edge of some shallow sea, a rock, you know, about two and a half kilometers wide, ten billion tons, moving maybe, like, two hundred times the speed of sound, it came crashing through the atmosphere and slammed into the Earth. The impact was so intense, so sudden, it's almost unimaginable, you know? Where Manson is today, in, like, a split second, became this huge crater, almost five kilometers deep and over thirty kilometers wide. And, you know, Iowa is usually all about limestone giving you hard mineral water, right? Well, not here. The limestone was totally obliterated, replaced by, like, intensely shocked basement rock. And that’s the rock that confused the well-digger back in 1912.
So, the Manson impact, it's actually the biggest one that's ever happened in the continental United States. For real. The crater is so big, that if you stood on one side, and the weather was clear, you could actually see the other side. I mean, it would make the Grand Canyon look small. But, unfortunately for people who like to see cool stuff, glaciers covered the crater and smoothed it out so today Manson is like a table top. Which is why no one has ever heard of the Manson crater, honestly.
At the Manson library, they'll show you, gladly, you know, some newspaper articles and a box of core samples from the 1991-1992 drilling project. Actually, they'll be quick to bring it out but you have to, you know, ask. There aren't, like, permanent displays or historical markers in town.
For most people in Manson, the biggest event that ever happened was a tornado back in 1979. It ripped through Main Street, tore up the business district. So, the good thing about being on flat land, you can see danger coming from far away. Basically, the whole town, they were all, like, standing at one end of Main Street, watching the tornado come for, like, half an hour, hoping it would change direction. It didn't. Then, they got out of there, but four people didn’t make it. So, nowadays, every June, the people in Manson have a week-long "Crater Days" festival. It was something that someone thought up to take people's minds off that anniversary, you know? It really has nothing to do with the crater, though. No one's really figured out how to take advantage of the invisible impact site.
"Every once in a while, someone comes in and asks where they can see the crater. We have to tell them there's nothing to see," said Anna Schlapkohl, the friendly town librarian. "They get a little disappointed and then they leave." But honestly, most people, even Iowans, have never even heard of the Manson crater. Even geologists didn't think it was a big deal. But then, in the 1980s, Manson, all of a sudden, became the most exciting place in the whole geological world.
The story starts in the early 1950s. There was this young, up-and-coming geologist named Eugene Shoemaker, who was doing a survey of Meteor Crater in Arizona. Now, Meteor Crater, it’s, like, the most famous impact site on Earth, and a popular tourist spot. But back then, not so much. The crater was still often called Barringer Crater, after Daniel M. Barringer, a mining engineer who bought it in 1903. Barringer was sure the crater was caused by a ten-million-ton meteorite loaded with iron and nickel. He was going to get rich digging it out, see. What he didn't know was that the impact had vaporized the meteorite and everything in it. For the next twenty-six years, he dug tunnels, found nothing, and wasted a ton of money.
By today's standards, the early studies of the crater were, like, pretty simple. One of the first researchers was G.K. Gilbert from Columbia University. He tried to simulate the effects of an impact by throwing marbles into pots of oatmeal. (Don't ask me why he did the experiments in a hotel room instead of a lab.) Somehow, Gilbert concluded that the craters on the moon were caused by impacts – pretty radical idea back then, honestly - but not the crater on Earth. Most scientists disagreed with even that. They thought the craters on the moon showed ancient volcanic activity, and that was it. Any clear craters on Earth were seen either as, you know, something else or as a rare phenomenon.
When Shoemaker came to study the crater, people generally thought it was caused by an underground steam explosion. Shoemaker didn’t know anything about underground steam explosions – because they don’t exist. What he did know a lot about were explosion sites. After college, his first job was surveying the explosion sites at the Yucca Flats Nuclear Test Site in Nevada. He came to the same conclusion Barringer had reached earlier. The crater didn’t have any volcanic activity, but plenty of other things, like weird forms of silica and magnetite, that suggested an impact from space. He became really interested, and started studying the problem in his free time.
Shoemaker first teamed up with a colleague named Eleanor Helin, and later with his wife, Carolyn, and an assistant named David Levy, and started doing systematic searches of the inner solar system. One week every month, they spent their time at the Palomar Observatory in California, looking for objects, mostly asteroids, that crossed Earth's orbit.
"In the beginning, only about ten of these things were found in the whole course of astronomical observation," Shoemaker recalled in a television interview. "Astronomers in the 20th century had basically abandoned the study of the solar system," he continued. "They turned their attention to the stars, to the galaxies."
What Shoemaker and his colleagues found was that outer space was way more dangerous than anyone had realized. Most people know that asteroids are rocky objects orbiting in a narrow space between Mars and Jupiter. In pictures, they always look like they’re crammed together, but the solar system is actually a huge place. The average asteroid is about a million and a half kilometers from its nearest neighbor. No one knows for sure how many asteroids are out there, but it's thought to be at least a billion. They might have become a planet, but Jupiter's gravity made it impossible, and still makes it impossible, for them to come together.
The first asteroid was discovered in the early 19th century. A Sicilian guy named Giuseppe Piazzi found the first one on the first day of the century. The asteroids were thought to be planets. The first two were named Ceres and Pallas. William Herschel figured out that they weren't planets at all but much smaller. He called them asteroids—Latin for "starlike." Not great, 'cause they’re not stars at all, you know. These days, they're sometimes called planetoids.
In the early 19th century, asteroid hunting became a popular hobby. By the end of the century, about a thousand asteroids were known. The problem was, no one kept good records. By the 20th century, it was often unclear whether a new asteroid was actually new, or just one that had been found before and then lost. Plus, astronomy had become so advanced, that few astronomers wanted to spend their time studying planetoids, you know, plain rocks. Just a few people kept up with the solar system, most notably the Dutch-born astronomer Gerard Kuiper, who the Kuiper Belt is named after. Thanks to his work at the McDonald Observatory in Texas, and then others at the Minor Planet Center in Cincinnati, Ohio, and the Space Watch project in Arizona, a lot of missing asteroids were recovered. By the end of the 20th century, only one known asteroid, an object known as Albert 719, was still missing. It was last seen in October 1911; it was finally rediscovered in 2000, eighty-nine years later.
So, from an asteroid research perspective, the 20th century was mostly about, like, a lot of statistics. It was only in the final few years that astronomers actually began counting and monitoring the rest. Something like twenty-six thousand asteroids have been named and cataloged, but half of them have been done in the last couple of years. You're only scratching the surface when there are a billion asteroids out there to be found.
And in some ways, this work doesn’t really matter. Finding an asteroid doesn’t make it any safer. Even if every asteroid in the solar system had a name and an orbit, we can’t know for sure what will knock one of them toward us. We can’t guess at what effect the rocks will have on the surface of the Earth. Rocks are flying around in space, we have no clue what they’re doing, you know? Any asteroid in outer space that has a name might stay right where it is.
Imagine if Earth’s orbit was a road and we were the only car, right? But people are constantly crossing that road without looking. We don't really know ninety percent of these people, where they live, what their schedules are, or how often they cross the road. We just know that, every so often, in some place, they walk across, and we're driving down that road at a hundred thousand kilometers an hour. As Steven Ostro of the Jet Propulsion Laboratory put it: "If you could turn on a light and illuminate all the asteroids larger than ten meters or so that cross the Earth, you would see about a hundred million of these objects in the sky." So, instead of seeing two thousand twinkling stars in the distance, you'd see hundreds of millions of fast-moving things nearby. "They're all capable of hitting the Earth. They're all moving at different speeds in slightly different directions across the sky. It’s very spooky." Yeah, it is pretty spooky, 'cause they're there. We just don't see them.
It’s believed -- just a guess based on the rate at which things hit the Moon -- that about two thousand asteroids big enough to threaten civilization regularly cross our orbit. But even a pretty small asteroid - house-size, you know? - could destroy a city. The smaller asteroids that cross Earth’s orbit almost certainly number in the hundreds of thousands, maybe even millions, and they're practically impossible to keep track of.
The first potentially dangerous asteroid wasn’t discovered until 1991. That was after it already passed us. It was named 1991 BA; it was found to have missed the Earth by a hundred and seventy thousand kilometers, which is like, a bullet going through your sleeve without touching your arm. Two years later, another, larger, asteroid just missed the Earth, coming within a hundred and forty-five thousand kilometers—the closest shave ever recorded. It, too, was discovered after it had already gone by. Tim Ferris wrote in *The New Yorker* that near misses like this probably happen two or three times a week without anyone knowing it.
A two-hundred-meter object probably wouldn't be spotted by telescopes on Earth until it was just a few days away. And that's only if that telescope was pointed in the right direction, which is unlikely, since there aren’t many people searching for these things. It's often said that the number of people in the world actively searching for asteroids is less than the number of employees in a typical McDonalds. (Actually, there are a few more these days, but not many.)
While Eugene Shoemaker was trying to bring attention to the potential dangers in the inner solar system, something else was quietly happening in Italy, something that seemed totally unrelated. In the early 1970s, near the town of Gubbio in Umbria, Walter Alvarez, a young geologist from the Lamont-Doherty Laboratory at Columbia University, was doing field work in a gorge called Bottaccione Gorge. He became curious about a thin layer of reddish clay. The clay layer divided ancient limestone into two layers, one from the Cretaceous period and one from the Tertiary period. This is known as the K-T boundary. It marked the sudden disappearance from the fossil record, sixty-five million years ago, of the dinosaurs and about half the other species on Earth. Alvarez couldn’t figure out how such a thin layer of clay, just six millimeters, you know, could account for something so dramatic in the history of Earth.
At the time, the general view of the dinosaurs' extinction was still what it was a century before, back in Charles Lyell’s day—that it happened over millions of years. But this thin layer of clay seemed to show that, in Umbria at least, things happened very suddenly. The problem was, in the 1970s, no one studied how long it took to accumulate such a layer of clay.
Alvarez almost certainly wouldn’t have bothered to worry about this, but luckily, he had a really good connection to someone on the outside, someone who could help out -- his father, Luis. Luis Alvarez was a famous nuclear physicist who had won the Nobel Prize in physics. He always thought his son’s love of rocks was a little embarrassing, but he became interested in the problem. He wondered if the answer might lie in dust from space.
Every year, Earth collects about thirty thousand tons of "cosmic spherules"—basically, space dust. Which would be a big pile, but when you spread it around the entire planet, it's almost nothing. Scattered in the dust are rare elements, rare on Earth, that is. One of these is the element iridium. Iridium is a hundred times more abundant in space than in the Earth’s crust (it’s thought that most of it sank to the Earth’s core early in Earth’s history).
Luis Alvarez knew that a colleague at the Lawrence Berkeley Laboratory in California, named Frank Asaro, had invented a technique, using neutron activation analysis, to precisely measure the chemical makeup of clay. The technique involved bombarding a sample with neutrons in a small nuclear reactor, and counting the released gamma rays. It was very intense work. Asaro had previously used the technique to analyze pieces of pottery. Alvarez thought that if they could measure the amount of a rare element in his son’s clay samples, and then compare the amount with the rate that the element was deposited each year, they could determine how long it had taken to form. One afternoon in October 1977, Luis and Walter Alvarez went to visit Asaro to ask him if he would do a few crucial tests for them.
It was a bit of a strange request. They were asking Asaro to spend months making careful measurements of geological samples just to confirm something that seemed obvious from the start—that the clay layer had formed quickly, you know, since it was so thin. No one expected it to lead to anything important.
"Well, they were very nice and very persuasive," Asaro recalled. "It looked like a fun challenge, so I agreed to try it. Unfortunately, I had a lot of other things to do, so it was about eight months before I got around to it." He checked his notes from the time. "At 1:45 p.m. on June 21, 1978, we put a sample into the detector. The machine ran for two hundred and twenty-four minutes and we could see that we were getting interesting results, so we shut it off to take a look."
The results were totally unexpected, and the three scientists thought they must have made a mistake. The Alvarez sample contained three hundred times more iridium than normal. Over the next few months, Asaro and his colleague Helen Michel worked for up to thirty hours at a time ("Once you get started, you just can’t stop," Asaro explained), analyzing samples, and they always got the same results. They also tested samples from other places—Denmark, Spain, France, New Zealand, Antarctica. The results showed that the iridium layer was global and that amounts everywhere were extremely high, in some places five hundred times more than normal. Something big had clearly happened, possibly a disaster, to produce such a striking isotopic signal.
After a lot of thinking, the Alvarezes concluded that the most likely explanation – at least, it seemed likely to them - was that an asteroid or comet had struck Earth.
The idea that Earth sometimes gets hit by big things wasn’t exactly brand new, like it might seem today. Back in 1942, Ralph B. Baldwin, an astronomer at Northwestern University, had suggested the possibility in an article in *Popular Astronomy*. (His article was published in this magazine because no academic publisher would run it.) At least two other scientists, astronomer Ernst Opik and chemist and Nobel laureate Harold Urey, had also supported the idea at different times. Even in paleontology, the idea wasn’t unknown. In 1956, M.W. Laubenfels, a professor at Oregon State University, wrote in the *Journal of Paleontology* that dinosaurs might have been hit by a deadly impact from space, which was pretty much a precursor to the Alvarez theory; and in 1970, Dewey J. MacClaughlin, the president of the Paleontological Society of America, suggested at the society’s annual meeting that an extraterrestrial impact could have caused the earlier so-called "Frasnian extinction."
Just to emphasize that the idea wasn’t brand new at this point, a Hollywood studio made a movie in 1979 called *Meteor* (It's five miles wide...traveling thirty thousand miles per hour—there's nowhere to hide!). It starred Henry Fonda, Natalie Wood, Karl Malden, and a big rock.
So, people shouldn't have been surprised when the Alvarezes announced at a meeting of the American Association for the Advancement of Science that they thought that the extinction of the dinosaurs wasn’t just part of a gradual process that happened over millions of years, but a sudden explosive event.
But they were surprised. Almost everyone thought that it was an unbelievable heresy, especially in paleontology.
"Well, you have to remember," Asaro recalled, "we were outsiders in this field. Walter was a geologist who specialized in paleomagnetism; Luis was a physicist; I was a nuclear chemist. And here we were telling paleontologists that we’d solved the problem that had bothered them for over a century. Not surprisingly, they didn't accept our ideas right away."
Luis Alvarez joked: "We were caught practicing geology without a license."
But there were deeper reasons that people hated the impact theory. Since Lyell’s day, gradualism had been a cornerstone of natural history. By the 1980s, catastrophism was seen as outdated, practically unbelievable. For most geologists, the idea of a big destructive impact, as Eugene Shoemaker pointed out, "violated their scientific religion."
It didn’t help that Luis Alvarez was openly dismissive of paleontologists and their contributions to scientific knowledge. "They're more like stamp collectors," he wrote in an article in *The New York Times* that still stings.
Opponents of the Alvarez theory offered a lot of different explanations for the iridium layer – for example, they argued that it was produced by the steady volcanism of the Indian Deccan Traps, and they insisted that, according to the fossil record in the iridium layer, there was no evidence that the dinosaurs disappeared suddenly. Charles Officer of Dartmouth College was one of the loudest opponents. He argued that the iridium was deposited by volcanism, even though he admitted he couldn’t prove it. As late as 1988, more than half of American paleontologists who were surveyed still believed that the extinction of the dinosaurs had nothing to do with an asteroid or comet impact.
One thing that could have supported the Alvarez theory, something the opponents were lacking, was an impact site. That’s where Eugene Shoemaker came in. Shoemaker had a connection in Iowa—his daughter-in-law taught at the University of Iowa—and he knew about the Manson crater from his own research. The attention shifted to Iowa, thankfully. Geology is a really local thing. Iowa is a flat state without a lot of cool geology. As a result, things tend to be calm in Iowa. There are no tall mountains or moving glaciers, no big reserves of oil or precious metals, no signs of flowing lava. If you’re a geologist hired by the state of Iowa, most of your job is assessing the "manure management plans" that "confined animal workers"—hog farmers—are required to submit regularly. Iowa has fifteen million pigs, so there is a lot of manure to manage. I'm not mocking this -- the work is very important to keep Iowa’s water supply clean. Even the strongest will can't escape the lava bombs on Pinatubo or the cracks in the Greenland ice cap while looking for ancient life-bearing quartz. So, we can imagine how excited the Iowa Department of Natural Resources must have been when, in the mid-1980s, the world’s geological community focused on Manson and the Manson crater.
The Trowbridge Building in Des Moines is a red brick building that was built at the turn of the century. It’s home to the University of Iowa’s earth science department, and the geologists for the Iowa Department of Natural Resources work up in the attic. No one can really remember how or why the state's geologists ended up inside an academic building, but the feeling you get is that space is limited, because the offices are cramped, the ceilings are low, and things are difficult to get to. When someone takes you inside, be ready to go over a ridge and be helped through a window into a room.
Ray Anderson and Brian Witzke worked here, spending their working days among piles of newspapers, magazines, charts, and rock samples. (Geologists have always been big users of paperweights.) In a place like this, if you want to find something—an extra chair, a coffee cup, a ringing telephone—you have to move a lot of things first.
"All of a sudden, we were in the middle of this stuff," Anderson recalled. "It was an exciting time."
I asked him about Eugene Shoemaker. Shoemaker seems to be a figure who is widely respected. "He was really great," Witzke replied right away. "Without him, it wouldn’t have gone anywhere. Even with his support, it still took two years to get things started. Drilling is expensive, and it cost about a hundred and fifteen dollars per meter, more than it does now, and we needed to drill almost a thousand meters deep."
"Sometimes deeper," Anderson added.
"Sometimes deeper," Witzke agreed. "In a few places. So, you need a lot of money. It would definitely be over our budget."
So, the Iowa Geological Survey and the U.S. Geological Survey decided to work together.
"At least we thought we were working together," Anderson said with a smile.
"Actually, it was a learning experience for us," Witzke went on. "There was a lot of pseudoscience during the project—some people quickly came to conclusions that weren’t always tested." One time, at the annual meeting of the American Geophysical Union, Glenn Izett and C.L. Pillmore of the U.S. Geological Survey announced that the Manson crater happened at the exact time as the extinction of the dinosaurs. The statement got a lot of attention from the press but was not really ready. If you checked the numbers, the Manson crater was not only smaller but nine million years too early.
It was a setback for them. Anderson and Witzke first heard the news when they were at a meeting in South Dakota. They saw people coming up to them with pitying looks, saying, "We heard you lost the crater." Izett and the other scientists from the U.S. Geological Survey had announced new numbers that showed that the Manson crater hadn’t caused the extinction of the dinosaurs. It was news to Anderson and Witzke.
"It was pretty shocking," Anderson recalled. "I mean, we had something really important, and then suddenly we lost it. But, even worse, we realized that the people we thought were working with us hadn’t bothered to share their new findings with us."
"Why?"
He shrugged: "Who knows? We really learned that science can be dirty, if you’re playing on that level."
The search moved somewhere else. In 1990, a researcher from the University of Arizona named Alan Hildebrand happened to meet a reporter from the *Houston Chronicle*. The reporter knew of a really big circular structure. It was located about nine hundred and fifty kilometers south of New Orleans, near Progreso in Mexico, under Chicxulub in the Yucatán Peninsula. The structure was discovered by Pemex, the Mexican oil company, but the company's geologists thought it was volcanic, which totally fit with the thinking at the time. Hildebrand went to the site and quickly concluded that they had found the crater they were looking for. By early 1991, it had been pretty much decided that it was the impact site.
Still, a lot of people didn’t really understand the effects of an impact. Stephen Jay Gould wrote: "I initially remained strongly skeptical about the power of such an event... How could an object only ten kilometers in diameter inflict such damage upon a planet thirteen thousand kilometers in diameter?"
A chance to test this theory came soon enough. Shoemaker and Levy discovered Comet Shoemaker-Levy 9, and they quickly realized that it was on its way to Jupiter. For the first time, people were going to see a cosmic impact, and thanks to the new Hubble Space Telescope, they could see it really well. Most astronomers weren’t really hopeful, especially because the comet wasn’t one solid object, but a series of twenty-one pieces. "I expect," one person wrote, "that Jupiter will swallow the comets without so much as a burp." A week before the impact, *Nature* ran an article called "Big Fizzle About to Happen," claiming that the impact would just be a meteor shower.
The impact started on July 16, 1994, and lasted a week. It was bigger than anyone had expected -- possibly with the exception of Eugene Shoemaker. One piece of the comet, called Nucleus G, hit with a force of six hundred million megatons – which is about 75 percent of the power of every nuclear weapon. Nucleus G was just hill-sized, but it left an Earth-sized wound on the surface of Jupiter. It was a devastating blow for people who criticized the Alvarez theory.
Luis Alvarez never knew about the discovery of the Chicxulub crater or Comet Shoemaker-Levy. He died in 1988. Shoemaker also died too early. On the third anniversary of the Jupiter impact, he and his wife were killed in the Australian outback. He went there every year to look for impact sites. On a dirt road in the Tanami Desert, they came over a hill and were hit by another car. Shoemaker died quickly. His wife was injured. Some of his ashes were sent to the moon on the Lunar Prospector spacecraft, and the rest were scattered around Meteor Crater.
The crater that Anderson and Witzke had wasn’t the reason for the extinction of the dinosaurs. "But we still have the largest and best preserved impact site in the continental United States," Anderson said. (To keep the Manson crater at the top, the wording needs to be a little flexible. Other craters are bigger – especially the Chesapeake Bay, which was identified as an impact site in 1994 – but they are either offshore or deformed.) "The Chicxulub crater is under a few kilometers of limestone, and mostly offshore. Which makes it difficult to study," Anderson went on. "But the Manson crater is totally accessible. It's buried underground, in a pretty original state."
I asked them how much warning we’d have if a similar rock was heading our way today.
"Oh, probably none," Anderson said casually. "It doesn't heat up until it's close enough to be seen with the naked eye, and it won't heat up until it's in the atmosphere. At that point, it will probably hit the Earth in one second. It will be going dozens of times faster than the fastest bullet. Unless someone found it with a telescope, and that’s not sure, it would be a total surprise."
The force of an object hitting the Earth depends on a lot of things—including the angle at which it entered the atmosphere, its speed and path, whether it collided head-on or at an angle, and its mass and density—things that we can't know millions of years after the fact. But scientists can do something—Anderson and Witzke have done it—measure the impact site and calculate the energy released. Based on those results, they can guess what must have happened, or, even more frighteningly, what would happen if it happened today.
When an asteroid or comet hits the atmosphere at cosmic speeds, it’s moving so fast that the air in front of it can't get out of the way. It's like the air in a bicycle pump: it gets compressed. Anyone who has used a pump knows that compressed air heats up really fast. It can raise the temperature to about sixty thousand degrees Celsius, or ten times the temperature of the surface of the sun. As soon as it hits our atmosphere, everything in the path of the meteorite—people, houses, factories, cars—would break down and disappear in fire, like a film of rubber.
One second after entering the atmosphere, the meteorite would hit the surface of the Earth. There, the people of Manson were going about their business. The meteorite would instantly vaporize and explode. The explosion would blow away a thousand cubic kilometers of rock, soil, and overheated gases. Anyone within two hundred and fifty kilometers who didn't die from the heat as the meteorite entered the atmosphere would be killed by the explosion. The first shock waves would spread out at almost the speed of light, destroying everything in their path.
For people outside the immediate disaster area, the first feeling would be a flash of light—the brightest flash a human eye has ever seen—followed by a terrifying scene, like the end of the world had come, lasting a few moments or a couple minutes: a rolling black curtain moving forward at a few thousand kilometers per hour, blocking the whole view, reaching for the sky. It comes silently, because it’s moving so much faster than the speed of sound. Someone in a tall building in Omaha or Des Moines would see a blur and then disappear.
Within minutes, in a wide area from Denver to Detroit, including Chicago, St. Louis, Kansas City, the Twin Cities—the whole American Midwest—everything standing would be flattened or on fire, and almost every living thing would be killed. People as far away as fifteen hundred kilometers would be blown off their feet, torn apart, or beaten down. Beyond fifteen hundred kilometers, the damage would start to decrease.
But that’s just the first shock wave. We can only guess at the damage from it, but it would definitely be really bad, you know? Global. The impact would certainly set off earthquakes that would be very destructive. Volcanoes around the world would start to rumble and release fire. Tsunamis would rise and move toward distant shores, causing a lot of damage. Within an hour, the Earth would be dark, and burning rocks and other pieces would be flying everywhere, turning most of the planet into a fiery hell. Some people guess that at least a billion and a half people would die by the end of the first day. Big problems with the ionosphere would break down communications everywhere, so survivors wouldn’t know what was happening somewhere else, or where to go. Also, it wouldn’t matter much, anyway. One commenter said that running would mean "choosing slow death over quick death. No matter how you change your location, the amount of people who die won't change much, because the ability of the Earth to support life would generally decrease."
The smoke and ash from the impact and the fires that followed would certainly block the sun for months, or maybe years, breaking growth cycles. Researchers at Caltech analyzed iridium deposits from the K-T impact and concluded that it affected the Earth’s climate for about ten thousand years. This could be used to prove that the extinction of the dinosaurs was quick and complete. We can only guess at how well or if humans would deal with something like this.
And remember, these things could come out of nowhere, with no warning.
Let's just imagine that we saw it coming. What would we do? Everyone thinks that we could shoot a nuclear warhead and blow it to pieces. However, there are a few problems with that. First, John S. Lewis says that our missiles can’t really work in space. They don’t have the ability to escape Earth’s gravity; even if they did, we don't have the equipment to manage them and let them fly for tens of millions of kilometers. We can't even send a spaceship cop out there to do it for us, like in the movie *Deep Impact*; we don't have rockets to send people to the moon. The last one of those rockets—the Jupiter V rocket—was retired years ago, and there isn't a replacement. We can't even build one quickly, because the blueprints for the Jupiter rocket were destroyed in a surprise spring cleaning at NASA.
Even if we managed to hit the asteroid with a warhead and break it up, we'd probably just turn it into a bunch of rocks; those rocks would then come crashing down on us one after another like Comet Shoemaker-Levy hit Jupiter – except that the rocks would be really radioactive. Tom Gehrels from the University of Arizona, who looks for asteroids, thinks that even one year of warning wouldn't be enough time to take action. However, there’s a greater chance that we wouldn’t see anything—even a comet—until it was six months or so away, which would be too late. Comet Shoemaker-Levy 9 had been orbiting Jupiter in a pretty obvious way since 1929, but no one noticed it for more than half a century.
It’s difficult to measure these things, so we'd have to wait until pretty much the last minute—a few weeks anyway—until we know if a collision is certain. We'd be living in uncertainty. It would definitely be the most interesting few weeks in the history of the world. Just imagine how big of a party we'd have if it all went safely.
"So, how often do things like the Manson impact happen?" I asked Anderson and Witzke.
"Oh, about every million years, on average," Witzke said.
"Remember," Anderson went on, "this was just a small event. Do you know how many extinctions are related to the Manson impact?"
"No," I answered.
"None," he said with a weird look. "There were no extinctions."
Of course, Witzke and Anderson quickly added—pretty much at the same time—that a lot of places on Earth were seriously damaged, like it had been destroyed in a few hundred kilometers. Still, life is tough. After the dust cleared, there were enough survivors that no species disappeared forever.
Seems like it’s hard to kill a species, which sounds good. The bad news is, this good news isn’t really guaranteed. And, you don't even have to look to space to see something scary.