Catastrophe: An Investigation Into the Origins of the Modern World (37 page)

Now, with the asteroid plunging toward Earth, its apparent brightness would have increased almost ninefold within four minutes, so that two minutes before zero hour, it would have been 250 times brighter than Venus, with an apparent diameter equivalent to a quarter of the moon’s.

Then, just eight seconds from impact, this invader from outer space would have hit the earth’s atmosphere—and for the first time would have produced its own light both directly and indirectly.

For just a few seconds prior to collision it would have become the brightest object in the sky. Observers three hundred miles away would have seen a fireball as bright as the sun. Observers thirty miles away would have witnessed a brief aerial light show a hundred times brighter than the sun.

Most likely coming in at an angle of between 30 and 60 degrees, and at a speed of forty thousand miles per hour (having been accelerated some 25 percent by Earth’s gravity), the asteroid’s surface would have been hotter than the surface of the sun (nearly 11,000 degrees Fahrenheit).

But that would not have been the main source of the light. Most of that would have been generated by the trillions of air molecules through which the asteroid passed. Through friction, some of the vast kinetic energy of the asteroid would have heated the air molecules to a blistering 45,000–55,000 degrees Fahrenheit!

If the 535 event was caused by an asteroid, it would certainly have had to be a deep-ocean impact. First of all, a land impact would have created an enormous crater, which, because it would have been formed relatively recently, would be known to the geological world. No recent craters of such large dimensions exist on land.

What’s more, in order for the dimming of the sun to have lasted twelve to eighteen months and for the climatic events to have lasted so many years, something finer than normal dust had to have been hurled into the atmosphere. Most ordinary dust would have fallen out of the sky too quickly to generate such medium- and longer-term effects. Volcanoes can achieve this by forcing huge quantities of sulfur into the stratosphere, which become sulfuric acid aerosols, capable of staying aloft and directly changing weather for several years.

But asteroids don’t generate much sulfur. So what could such an impact do to the atmosphere that would produce those long-lasting sun-dimming and other climatic phenomena? The answer lies not in the asteroid itself but in the medium it lands in. If it hit ocean, huge quantities of water—both vaporized and in liquid form—would have been injected directly into the stratosphere. This water would have formed rapidly into high-altitude stratospheric clouds of tiny ice crystals, which would in turn have restricted and scattered the sun’s beams, creating an apparently dimmed sun, a drop in temperature, and a lot of climatic repercussions over a considerable period.

If the 535 event
was
asteroid-caused, with an ocean impact, the cosmic rock—all hundred billion tons of it—would have vaporized within a quarter of a second on impact with the water and the ocean floor. Perhaps 10 percent of the asteroid’s kinetic energy—around twenty quadrillion joules’ worth of it (equivalent to a five-million-megaton nuclear explosion)—would then have been transferred to the surrounding ocean in the form of heat and water movement. (Five million megatons is equivalent to a hundred thousand of the largest nuclear bombs.)

One hundred cubic miles of water would have been vaporized almost instantly, generating 140,000 cubic miles of water vapor, which would have exploded skyward at more than twenty thousand miles per hour, rapidly penetrating the stratosphere. And around the vaporized impact site, a huge wave—between fifteen and twenty miles in height—would have reared up out of the ocean, driven by the shock wave created by the impact. Like the high-speed vapor stream, the top part of the wave would have penetrated the stratosphere.

Moving outward at around a thousand miles per hour, the wave would have gradually lost height, so that five hundred miles from the impact site, it would have been only two hundred feet high.

Just as an asteroid collision with Earth would have produced mid-sixth-century-style climatic mayhem, a comet would have had much the same effect. But because comets are less dense than asteroids, yet normally travel faster, an equivalent energy release on impact would have required a comet nucleus with a diameter of about four miles. And although there are millions more comets traveling around the sun than there are asteroids, comets hit the earth ten times less often than asteroids do, mainly because comets normally come nowhere near our planet.

Indeed, the most remote of them have solar orbits that take them 750 times farther out into space than Pluto, the most distant of the sun’s planets. Out of the ten thousand billion comets estimated to be orbiting the sun, only a few thousand come within even three hundred million miles of the earth—
or
the sun!

Very, very few ever actually hit our planet. It’s estimated that a comet of the size required to generate mid-sixth-century-style climatic chaos collides with the earth on average only once every five hundred million years. But although comet impacts may be extraordinarily rare, they still have to be considered as theoretically possible culprits for the 535 catastrophe.

Comets are 70 percent frozen water, 15 percent frozen carbon monoxide and other gases, and 15 percent dust, stones, and possibly even boulders. Most comets are simply frozen lumps of ice and dust with temperatures as low as minus 454 degrees Fahrenheit. But a tiny number of them come briefly close enough to the sun to begin to “melt” (technically, they sublimate). Three hundred million miles out in space they then begin to form atmospheres—derived from their “melting” frozen-gas bodies. By the time the comet is 250 million miles from the sun, elements of that atmosphere and the freed-up dust within it begin to be pushed out to produce one (or sometimes two) “tails,” which can be up to 100 million miles long. It is the physical pressure of light (photons) on tiny dust particles that, quite literally, pushes the dust outward to form a tail. The gas molecules making up the atmosphere form the rest of the tail system by being given an electric charge and then by being carried along by ionized atomic particles shot out by the sun (the so-called solar wind).

The only comet impact ever actually witnessed and recorded by scientists was the collision of the comet Shoemaker-Levy 9 with Jupiter in 1994. In that event, a 2.5-mile-diameter comet nucleus broke up while temporarily orbiting the giant planet, and the twenty-one resultant fragments plunged at 2,200 miles per hour into Jupiter’s atmosphere. There was then a huge explosion that created a nuclear-style mushroom cloud extending two thousand miles above the cloud tops, billowing spectacularly into outer space, way outside the Jovian atmosphere. This massive cloud was caused by simply the largest fragment—a lump of ice and dust just half a mile across.

If it was a four-mile-diameter comet that caused the
A
.
D
. 535 event, the explosion would have been twenty times as great as the one on Jupiter in terms of energy release!

A
lthough the comet or asteroid scenarios would explain the size and nature of the sixth-century catastrophe, there are a number of serious objections to either of these explanations.

First of all, an asteroid (or comet) impact, by definition, releases virtually all its energy in less than a second. The explosion caused by a large asteroid or comet hitting the ocean at high speed would have caused a vast circular wave, consisting of hundreds of cubic miles of water, to rear up around the impact site, penetrating deep into the stratosphere. The impact itself and the collapsing wall of water would then have sent a series of huge tidal waves hurtling across the ocean. Ninety-nine percent of each wave structure would have been deep below the ocean surface—stretching up to 3 miles down. Each visible wave would have been merely the surface symptom of a massive movement of subsurface water. Thus, at any one time, the wave motion would have involved thousands of cubic miles of water. On the surface, well away from the impact site, say two thousand miles, the tidal wave would probably have been only fifty feet high.

But as the wave approached land and entered shallower water, the percentage of the wave structure above sea level would have massively increased. Indeed, by the time the largest tidal wave reached the thousands of miles of coastline surrounding the ocean, it would have been perhaps three hundred to nine hundred feet high, enough to devastate hundreds of thousands of square miles of coastal land. Only where high cliffs or coastal mountains blocked the tidal wave’s path would the devastation have been limited. But where coastal plains were low-lying or where deep river valleys stretched inland through coastal mountains, the destruction would have been total, with the tidal wave penetrating dozens or even hundreds of miles inland in some areas.

The problem is that it would be nearly impossible for such a coastal catastrophe to have gone unnoticed by modern archaeologists, geologists, and historians. A tidal wave of such proportions would have rivaled Noah’s flood in any legend, would have been recorded in horrified terms by any literate societies affected, and would have been detected by archaeologists and geologists on any archaeological and geological site anywhere along thousands of miles of the relevant ocean’s coastline.

It is virtually unthinkable that an impact event of that magnitude only fifteen hundred years ago could be unknown to science today.

Another clinching piece of evidence that points away from a cosmic impact explanation and toward the third option—a volcanic one—is this: Buried up to sixteen hundred feet below the surface of the Greenland and Antarctic ice caps is a telltale layer of ice contaminated by sulfuric acid of volcanic origin that was almost certainly associated with the twelve- to eighteen-month-long sun-dimming event of 535–536 and the subsequent climatic chaos.

Back in 1978, a joint Danish-Swiss-U.S. scientific team landed on the south Greenland ice cap in several large freight aircraft specially fitted with giant skis. The planes carried massive quantities of equipment, including generators, refrigeration units, prefabricated living quarters, and a huge drill.

This latter piece of hardware was used to extract more than a mile of ice core in about six-foot lengths. Working in temperatures as low as minus 22 degrees Fahrenheit, engineers and scientists drilled in three shifts, twenty-four hours a day, going deeper and deeper into the ice cap at roughly 400 feet per week.

Then, early in the second year of the operation, after just a few weeks of drilling, the team extracted some lengths of core covering the second quarter of the sixth century
A
.
D
. Back in a laboratory at Copenhagen University, chemical analysis of this sample revealed that there had been two substantial volcanic eruptions. These same eruptions were then detected in a second core drilled in summer 1990 in central Greenland.

Because the dating of Greenland ice cores at that time depth is only roughly accurate (say, to within five or eight years, depending on the core concerned), the two cores each gave slightly different dates for the same sulfuric acid layer. Dates are determined by simply counting back annual layers of snow—so unusually high precipitation can sometimes appear to add extra years, making an acid layer seem marginally older than it is.

The annual layers of snow (which under many tons of pressure turn into ice) are detected by measuring the normally regular annual variations in the percentage of snow consisting of so-called heavy water. Most water molecules, in liquid or frozen state, consist of two atoms of hydrogen and one oxygen atom with an atomic weight of 16. However, around 0.2 percent of water consists of molecules made up of two hydrogen atoms plus one oxygen atom of atomic weight 18. But the actual percentage of heavy water being precipitated onto a given point on the earth’s surface at any given time depends upon the weather. The proportion goes down to around 1,960 parts per million in very cold conditions and up to 2,000 parts per million in very warm conditions. In a polar environment the amount ranges from 1,960 parts per million in winter up to 1,975 parts per million in summer. Thus, by studying the regular (normally annual) rise and fall of heavy-water content in ice cores, scientists can construct an ice-core chronology and obtain dates for volcanically derived acid concentrations detected in the core. The system is accurate to within a few years, but unseasonable temperature fluctuations or substantially reduced levels of precipitation can distort the dating, especially at relatively large time depths.

For eruption one, the high-altitude GRIP core gave an apparent date of 527, while the lower-altitude DYE 3 core (three hundred miles to the south) yielded an apparent date of 530. The volcanic explosion must have been very substantial, as evidence from the GRIP core shows that acid-rich snow was falling at the GRIP site in Greenland for more than two years and at the DYE 3 site for at least a year.

For eruption two, the high-altitude GRIP core provided an apparent date of 532, with acid snow falling on the site for just over a year. For this same eruption, the DYE 3 core yielded an apparent date of 534 and evidence of acid snowfalls of around four months.