The Mars Mystery: The Secret Connection Between Earth and the Red Planet Page 20

  The essence of the orthodox “refutation” or “debunking” is that there is no known mechanism sufficiently powerful to set off crustal displacements and that such events are therefore “geophysical impossibilities.” In this way intriguing pieces of evidence marshalled by crustal-displacement theorists have been repeatedly swept under the carpet. Even if an adequate mechanism has not yet been identified, however, the latest discoveries must surely shake the orthodox consensus. For what the Cal Tech researchers are talking about—this time under the banner of peer-reviewed respectability that Science represents—is nothing more nor less than a fully fledged displacement of the Earths crust that could not have failed to have cataclysmic consequences.

  It should therefore come as no surprise to learn that the extinction of an estimated 80 percent of all genera of life occurred at this time.35 With almost miraculous speed, life then bounced back and the extinction was followed by

  a profound diversification that saw the first appearance in the fossil record of virtually all animal phyla living today. With relative evolutionary rates of more than 20 times normal, nothing like it has occurred since.36

  This was the so-called Cambrian explosion, and it was indeed the greatest diversification and expansion of life that the earth had ever seen. Since then scientists believe that at least five further great extinctions—and about a dozen smaller ones—have occurred.37 Evidence is growing that all these extinctions, as well as the gigantic crustal displacement that preceded the Cambrian explosion, may have been sparked by high-speed collisions with massive chunks of cosmic rubble on Earth-crossing orbits.38 If they were to release sufficient impact energy, such collisions might theoretically provide the missing mechanism that scientists have been looking for that could set the crusts of entire planets in motion. One might even imagine a scenario for Earth in which all major impacts result in extinctions, but a sufficient energy threshold has to be crossed—or other conditions fulfilled—before an impact can trigger a crustal displacement.

  IMPACTS AND EXTINCTIONS

  One of Earths five big extinctions took place at the juncture of the Permian and Triassic periods around 245 million years ago. Under mysterious circumstances 96 percent of all oceanic species and 90 percent of all land-dwelling species were wiped out at a stroke.39 The radio astronomer Gerrit Verschuur, now professor of physics at the University of Memphis in Tennessee, comments:

  No localized flicker of nature can account for the sudden demise of so many species at the same time. It required a global phenomenon of staggering proportions…. Life on Earth very nearly came to an end. Words can barely begin to describe the enormity of such a catastrophe.40

  Evidence has been presented linking this extinction with an impact—although geologists are be no means unanimous on the matter.41 By contrast there is certainty regarding the later great extinction that took place 65 million years ago at the Cretaceous-Tertiary (K/T) boundary. Following breakthrough discoveries in the 1970s and 1980s,42 all scientists today accept that this event was caused by a gigantic object from space—an object at least 10 kilometers in diameter—that smashed into the northern tip of the Yucatan peninsula at a speed of approximately 30 kilometers per second.43 The resulting crater, now deeply buried beneath millions of years of accumulated sedimentation, has a diameter of almost 200 kilometers. It was first identified on gravitational maps made by surveyors looking for oil and subsequently confirmed by radioactive dating to be 65 million years old.44

  As we noted in chapter 4, this K/T Boundary Event caused the extinction of the dinosaurs. It is also estimated to have killed off 50 percent of all other genera; 75 percent of species; and a staggering 99.99 percent of all individual animals then living on Earth.45

  A GLOBAL CATACLYSM

  The sequence of events and what exactly happened to our planet 65 million years ago has been reconstructed by scientists (who are generally of the opinion that the K/T object must have been a comet). According to the geologist Walter Alvarez:

  About 95 percent of the atmosphere lies below an altitude of 30 km, so depending on the angle at which the impactor approached the surface, it would have taken only a second or two to penetrate. The air in front of the comet, unable to get out of the way, was violently compressed, generating one of the most colossal sonic booms ever heard on this planet. Compression heated the air almost instantaneously until it reached a temperature of four or five times that of the Sun, generating a searing flash of light during that one-second traverse of the atmosphere.

  At the instant of contact with the Earths surface, where the Yucatan peninsula now lies, two shock waves were triggered. One shock wave ploughed forward into the bedrock, passing through a three-kilometer-thick layer of limestone near the surface, and on into the granitic crust beneath…. Meanwhile a second shock wave flashed back into the onrushing comet.46

  Gerrit Verschuur takes up the story:

  Within an hour of impact the rumble of the earth is heard around the world and earthquakes toss everything into the air. With magnitude 12 to 13 on the Richter scale the earthquake mangles solid rock as the ground buckles. All around the planet the seismic shock rumbles. As it travels its energy begins to focus so that at the antipodes it gathers and the planets surface buckles and heaves 20 meters…. Eight hundred kilometers from the impact a tsunami more than a kilometer high washes over the North American continent to create ripples in the land that will be preserved and etched in geological strata for 65 million years to come…. A hundred meters of deposits dragged from the bottom of the sea cover the islands and the coastal regions of the mainland, and boulders the size of automobiles land 500 kilometers from the impact in a country later to be called Belize.47

  Despite the tidal waves there is evidence that a global firestorm must have raged for several days after the K/T impact until it finally burned itself out. Scientists report the discovery of “a pervasive soot and charcoal layer … which indicates that upward of 90 percent of the biomass was incinerated at that time in global wildfires.”48

  Soon the world fell into a sort of “nuclear winter” as dust and smoke hefted up into the atmosphere by the impact and by the fires blotted out the light of the sun for several months.49 Alvarez is of the opinion that “the land became so dark that you could not have seen your hand in front of your face.”50 A long period of freezing shadowy gloom then followed, during which many of the animal species that had survived the initial effects of the impact would have perished from cold, hunger, and exposure. Photosynthesis was suppressed and all over the earth the food chain was interrupted.

  UNSEEN DANGERS

  The explosive energy of the K/T object has been estimated at 100 million megatons of TNT—that is, about 1,000 times greater than the object that made the 13-mile Giordano Bruno crater on the Moon in 1178.51 Yet an impact of either magnitude would be a civilization-destroying event—and perhaps the end of all mankind—if it were to afflict Earth today.52 Indeed, as we saw in part 1, sufficiently large impacts such as those that struck Mars at some point during its history are capable, under certain circumstances, of sterilizing an entire planet.

  Ours is a resourceful species that has survived through its ability to adapt to threats and to anticipate dangers. Is it not obvious from the terrible fate suffered by Mars, and from the evidence of past impacts on Earth and on the Moon, that we should pay attention to the possibility that unseen dangers may be lurking in the dark reaches of space among the planets of the solar system?

  19

  Signs in the Sky

  IN 1990, David Morrison, an astronomer at the NASA Ames Research Center, observed wryly that “there are more people working in one fast-food restaurant than there are professionals scanning the sky for asteroids.”1 This is no longer quite true today. Public funding for such work is still so miniscule as to be almost laughable—indeed, the grand total of all contributions from all governments worldwide rarely exceeded a million dollars a year from 1990 until the end of 1997.2 Nevertheless Spacewatch pro
grams that scan the sky for asteroids have been established in a number of countries, relying heavily upon concerned astronomers who are prepared to volunteer their time.3

  At Kitt Peak National Observatory in Tucson, Arizona, which does receive some of NASA’s limited Spacewatch funding, a team of astronomers is involved in a systematic long-term search for near-Earth asteroids using a 90-centimeter telescope and a CCD camera. The program is reported to have discovered “an average of two or three near-Earth objects each month, the smallest only 6 meters across.”4

  Related Spacewatch investigations include the Near-Earth-Asteroid Tracking Program of the U.S. Air Force observatory in Hawaii; the Planet-Crossing Asteroid Survey at Palomar Mountain in California; the asteroid search program of the Cote d’Azur observatory in Southern France; and the Anglo-Australian Near-Earth Asteroid Survey (which was terminated due to lack of funds in 1996).5

  Will more resources be forthcoming for such programs in the future?

  This is an area in which policymakers tend to be long on promises and short on action. But we do take it as a sign of an important change of heart—albeit one that has predictably not yet resulted in any more money—that the U.S. House of Representatives wrote the following clause into the NASA Authorization Bill of 20 July 1994:

  To the extent practicable, the National Aeronautics and Space Administration, in coordination with the Department of Defense and the space agencies of other countries, shall identify and catalogue within 10 years the orbital characteristics of all comets and asteroids that are greater than 1 kilometer in diameter and are in an orbit around the Sun that crosses the orbit of Earth.6

  Why greater than one kilometer in diameter? The reason is a generally held belief that human civilization could survive a collision with a half-kilometer object and might not survive a collision with an object more than one kilometer wide. But what about a swarm of half-kilometer objects—or of quarter-kilometer objects, for that matter—or even a swarm of Tunguska-sized bolides penetrating Earths atmosphere repeatedly, over hundreds of different locations, for a period of a week or two? Would that be survivable? And could it happen?

  CRATERS

  During the last two centuries astronomers have learned a great deal about the solar system and about near-Earth space—and nothing that they have discovered is reassuring. On the contrary, as our planet orbits the sun at a steady velocity of almost 110,000 kilometers per hour, we now know that it passes repeatedly through “lumpy” streams of cosmic debris. Most of the rubble takes the form of tiny meteors that burn up harmlessly in our atmosphere in the form of shooting stars. But there are also larger objects that explode in the sky and even more massive objects that make it to the ground. As we have seen, Earth during its long history has several times collided with such objects from space. Moreover, it is clear that the Tunguska and K/T events reported in the preceding chapter are by no means isolated incidents. According to the astronomer Sir Fred Hoyle, Earth could well have suffered more than 130,000 major impacts over the last billion years.7

  One worrying feature is that many impacts appear to have involved groups of objects rather than just individual projectiles. We have mentioned the prospect of “swarms of Tunguskas”—in itself a nightmarish possibility, as we shall see—but it is now clear from the geological record that the 10-kilometer object that caused the K/T event was also part of a swarm. At least a dozen other craters with dates indistinguishable from the K/T event have been found. These include the totally buried 35-kilometer “Manson structure” in Iowa state.8

  Because the earths surface is dynamic and subjected to continuous erosional and depositional forces, even the largest craters can and do disappear in matters of millions of years. In addition, because water covers seven-tenths of the surface of this planet, simple logic suggests that the majority of impacts must take place in the oceans—where they leave fewer long-term traces than impacts on land. Another important factor is that it is only since the late 1920s that impact craters have been recognized for what they are, having previously been wrongly attributed to volcanism, so this is a relatively new area of study.9 Nevertheless more than 140 major craters have now been firmly identified, distributed all around the earth, and about five more are found every year.10 Although some are as much as 200 million years old, surprising numbers of them are recent.11

  Interesting discoveries include a chain of craters in South America made by a swarm of small iron meteorites. The meteorites appear to have entered the atmosphere at a shallow angle, only surviving because of their iron (as opposed to stony) constitution and then impacting Earth along a narrow 18-kilometer track in the region of Campo del Cielo, Argentina.

  Individual meteorites of different sizes were well sorted by sequence of mass along the track, evidently by aerodynamic (drag) forces. Disruption of the parent body occurred at an altitude of several kilometers. Radiocarbon dating of charcoal from one of the craters suggests that the event occurred well within the time of human occupancy in South America, about 2900 b.c.12

  A second crater chain thought to be “no more than a few thousand years old” lies in the heart of the Argentinian pampas and was first spotted by an air force pilot flying overhead in 1989.13 It is 30 kilometers from end to end. Its craters are not circular, as is the case with vertical impacts, but elongated—the three largest are each four kilometers long by one kilometer wide. Numerous smaller craters “were evidently made by fragments hurled downrange.”14

  More than 10 percent of Earths craters larger than half a kilometer across have at least one companion crater nearby,15 and three of the largest impact structures on Earth are conspicuously paired with smaller ones: the Steinheim and Reis craters in Germany (46 kilometers in diameter and 24 kilometers in diameter, respectively), which are both 15 million years old; the Kamensk and Gusev craters in Russia, both 65 million years old; and the twin Clearwater Lakes in Canada in northern Quebec, east of Hudson’s Bay, which are 290 million years old.16

  Lake Manicougan in Canada is an impact crater 60 kilometers in diameter.17 The Sudbury structure in Ontario, containing one of the worlds largest deposits of nickel and other valuable metals, is now recognized as “a tectonically distorted impact crater that was initially about 140 kilometers in diameter.”18 The 100-kilometer-diameter Vredfort Dome in South Africa is an impact structure.19

  Astronomer Duncan Steel, head of Spaceguard Australia and founder of the Anglo-Australian Near-Earth Asteroid survey, estimates:

  We have yet to discover more than 1 percent of the impact structures on Earth…. Hundreds of craters are undoubtedly still hidden beneath the forest canopy of the Amazon basin, the tundra of the Arctic regions … the shifting sands of northern Africa and Arabia … [and] the 70 percent of Earth covered by water…. So far only one submarine crater has been found, the 60-kilometer-wide, 50-million-year-old Montagnais structure in the coastal waters of Nova Scotia.20

  Yet the inventory of Earth’s impact craters continues to grow. When set alongside the horrific scars of Mars and the pockmarked face of the Moon it should remind us that the solar system is and always has been a hazardous place—hazardous to all planets and all life in all past epochs and, obviously, still hazardous today.

  ASCLEPIUS AND HERMES

  In 1989 an asteroid with an estimated diameter of half a kilometer crossed Earths path. “Earth had been at that point in space only six hours earlier,” a House of Representatives committee report noted.

  Had it struck Earth it would have caused a disaster unprecedented in human history. The energy released would have been equivalent to more than 1,000 one-megaton bombs.21

  With the dimensions and stored kinetic energy of “a giant aircraft carrier traveling at a speed of 42,000 miles per hour,”22 this object was not detected by any astronomer until three weeks after it had thundered past us.23 Now catalogued as 4581 Asclepius, it came, at its closest, to within 650,000 kilometers of Earth.24

  This was a new record close passage—though we will see that
it did not stand for long. The previous closest passage had been registered in 1937 by Hermes, a somewhat larger asteroid (estimates of its diameter range between one and two kilometers).25 On the night before Halloween it approached Earth at alarming speed, “moving at up to 5 degrees an hour and completely crossing the sky in nine days.”26 The effect, according to an astronomer at the time, was “much like that obtained by standing near the railroad track when the evening express roars past.”27

  After staging this breathtaking flyby, Hermes vanished into the darkness of space and has never been seen again—an unsatisfactory state of affairs since past close passages make future close passages more likely.28 Hermes is therefore an object to be watched. We can be sure that it is still lurking in the solar system and there is a fair chance that it has crossed the track of our planets orbit more than once since 1937 but has simply not been spotted.29 Asteroids of this size are extremely easy to miss in telescopic surveys and, as we shall see, astronomers believe that several thousand of them may be circulating in our immediate neighborhood.

  INCOMING ASTEROIDS

  On Sunday, 19 May 1996, and again less than a week later on 25 May 1996, Earth was approached by two potentially apocalyptic asteroids. The first—catalogued as 1996 JA—zoomed past at a distance of about half a million kilometers and at an estimated speed of 60,000 kilometers per hour. Astronomers were able to give us only four days’ advance notice of its arrival on our cosmic front porch. The second, asteroid JG, was more than a kilometer in diameter and passed at a distance of about two and a half million kilometers.30 According to scientific calculations a collision between Earth and such an object