THE FATE OF THE DINOSAURS
by: Antony Milne

pg. 263

The 'final straw' came when the missile struck Earth. Firstly the missile, about one kilometer in diameter and weighing about 100 million tons, traveling at a speed of 25 km per second, would generate devastating kinetic energy and shock waves that would arise from an explosion in the atmosphere equivalent to 100,000 million tons of TNT. The temperature of the atmosphere in the first few minutes, as the missile passed through it, would have reached about 200 degrees C, and scorching winds would have reached speeds of 400 km per hour. Shards of blistering hot energy would have burst across the surface, melding rock particles and triggering volcanic eruptions. The nest stage would be for the atoms of gas in the atmosphere to be rearranged; i.e. nitrogen and oxygen would have been blended to become oxides of nitrogen. These could soon become nitric acids which produce nitrates in the soil, especially in conjunction with heavy rains.

THE BIG SPLASH
by: Dr. Louis A. Frank with Patrick Huyghe

Chapter 21 Death of the Dinosaurs

In looking for the source of the small comets, we ended up explaining far more than anyone ever expected. Any way of herding small comets into the Earth's vicinity was likely to bring in large comets al well. But while the everyday showers of forty-foot comets may have brought the ingredients for life to this planet, a storm of mile-wide comets would most likely spell death and destruction for much of like of Earth. Suddenly many parts of the puzzle began falling into place, beginning with why the dinosaurs disappeared 65 million years ago.

Much of the groundwork for such a scenario was laid in 1980 and the following years by a team of four scientists that included the late Luis Alvare, a physicist who won the Nobel Prize in 1968 for developing bubble chambers to investigate the structure of the nuclei of atom; his son Walter Alvarez, a geologist at Berkley; and Frank Asaro and Helen Michel, both nuclear chemists at the Lawrence Berkeley Laboratory. They had come to the conclusion that a mountain-sized object had hit the earth 65 million years ago and caused the extinction of much plant and animal life. They had focused mostly on the extinction of microscopic marine animals, the phytoplankton and zooplankton, as well as some larger marine organisms. But the dinosaurs had died rather suddenly and at the same time as well

The Great Extinction
by: Michael Allaby and James Lovelock

Chapter 5: The Barrel of Fire

The sea blew up. Transformed into incandescent gas, the ocean leaped upward with a roar that would have been heard on the other side of the world.

There could have been no warning. At least, there could have been no warning that might have helped any of the animals living on Earth at that time. Perhaps the more alert of them, the very quick-witted, might have caught a glimpse of a flash in the sky, might have begun to raise their heads. Were such reptilian heads protruding above the surface of the ocean? Were the seabirds -which existed by then and looked much like their modern descendants- whirling and screaming in their incessant search for food? Did they begin to notice the fire in the heavens? It is doubtful, and the observation would not have helped them.

This is not because the event would have been visible. Far from it. When the approaching planetesimal entered the outermost regions of the atmosphere, some 150 kilometers above the surface, it would have begun to shine more brightly than the sun.  Because of the angle it subtended, it would have appeared some 10 times larger than the Sun and as its temperature rose to some 18,000 degrees C -3 times hotter than the Sun- it would have become 100 times brighter.  No more than a second after it appeared it would have filled the sky. The observation of it would have been no more than a glimpse because any observer close enough to see it would have been burned to a cinder by the radiant heat that it preceded it. The sea immediately below the object would have begun to boil vigorously shortly before the impact.

For living organisms in its path, the end would have been quick. A planetesimal falling almost vertically to the surface at 20 kilometers a second would take less than 2 seconds to pass through the denser region of the atmosphere. Some comets may travel at up to 4 times that speed in relation to the Earth, and they would take proportionately less time to arrive. For countless millions of animals, all sleeping, grazing, stalking of prey, quarreling, courting, mating, would become oblivion.  The would cease to exist.

The explosion that tore the ocean apart would have been more violent than anything we have known in our history, more violent than anything we can imagine without help. To try to comprehend it we must break it down, to describe each of its appalling elements, one at a time.

In the first place, we must ask you to accept our assertion that the object fell into the sea. It makes little difference to many of its immediate effects whether it fell on the sea or on land, but we have reasons for supposing that it fell somewhere in the middle of the North Atlantic, and we will give them later, in Chapter 6.

Let us begin with the size of the planetesimal. It had a diameter of 10 or 11 kilometers. This sounds little enough, but that is because we are comparing it with other members of the solar system. It is hardly large enough to qualify the body of the dignified title of "planet". It is much the same size as Phobos, one of the small, lumpy satellites of Mars. Phobos is about 13.5 kilometers long and 9.5 kilometers wide. Our Moon is much larger. The planetesimal is small on the cosmic scale, but that is the wrong scale. We should compare it with objects on the Earth itself.

Mount Everest is just over 8,850 meters high. That is to say, that highest peak of Everest (although it may still be growing higher because of the crustal movements that formed the Himalayas have not ceased) stands about 8.9 kilometers above sea level. If you imagine Everest standing on a column of rock, isolated so you can see it from a summit to sea level as it were, and if you imagine the planetesimal set upon the ground beside it -without sinking into the depression caused by its great weight- the planetesimal would be 1 or 2 kilometers taller than Everest, and much wider. It would dwarf the mountain.

It would present a hazard to aviation. Only military aircraft and intercontinental civil airliners fly at altitudes of 10 kilometers or more. A Concorde would clear it comfortably, but a Boeing 747 or a Tristar would have to make a detour around it unless the captain was prepared to entertain his passengers with a little low level flying.

We are dealing, then, with an object that is smaller on the cosmic scale but very large indeed on any scale that familiar to us on Earth. It was also very solid. It was a lump of rock no whit less solid than Everest itself, and it can have been no less dense, so 1 cubic meter of it would have weighed no less than 1 cubic meter of rock from Everest. The Alvarez team has estimated its weight at between 100 billion and 1,000 billion tons. This allows plenty of room for refinement (Ganapath estimated 2,500 billion tons), but at least it gives and idea of the mass of the thing.

It approached the Earth at about 20 kilometers per second (nearly 45,000 miles per hour). The Earth itself moves in its orbit around the sun at 29.8 kilometers per second, but the numbers mean little.  Twenty kilometers is almost 60 times the speed of sound (Mach 1) at sea level in the atmosphere.  At Mach 60, the journey by plane from London to New York would take a fraction more than 4 minutes.  The airline would save money on catering and lose it in bar sales and workaholic executives would find themselves facing the 29 hour day of which they pretend to dream. The Columbia space shuttle orbits the Earth at about kilometers per second (about 18,000 miles per hour). A satellite in geosynchronous orbit, whose position remains constant about a point on the Earth's surface, travels at about 3 kilometers per second (6,700 miles per hour). An M16 rifle can fire a bullet at speeds of very nearly 1 kilometer per second (2,200 miles per hour). Since the speed of a high-velocity rifle bullet is something to which we can relate, let us use that. We are considering an object much larger and heavier than Mount Everest, made from solid rock and metal, approaching Earth at about 20 times the speed of a high-velocity bullet from a modern army rifle.

It was big and fast, and its impact released a great deal of energy. How much energy? We can calculate that because we have estimates for the mass and velocity of the planetesimal. Again, though, we produce a number -in this case about 1,000 billion ergs per square centimeter of surface- that means nothing. W.H. McCrea has related this number to something more familiar.(Proceedings of the Royal Society, Vol. 375, No. 1760, pp. 33-34, 1980). He estimates that the impact would have been more equivalent to the detonation of 100 trillion (100 million million) tons of TNT. How big is that?  How big is a number 1 followed by 14 zeros? The atomic bomb dropped on Nagasaki in August 1945 exploded with a force equal to about 20,000 tons of TNT: a 2 and four zeros. The planetesimal therefore arrived with as much energy as about 5 billion (5,000 million) Nagasaki-sized bombs.  To help us further, McCrea points out that had the energy been distributed over the surface of the Earth (which, fortunately, it was not) it would have amounted to about 10 Nagasaki-sized bombs on each and every square kilometer of the planet's surface: about twenty-six Nagasaki bombs per square mile.  If we suppose that the entire global armory of nuclear weapons can be measured as a few hundred billion tons of TNT equivalent, then we are trying to imagine the simultaneous explosion, in one place, of about 1,000 times that entire stockpile. It is hardly surprising that we find it difficult! We are attempting to describe a phenomenon that is far beyond anything we have ever experienced or that is recorded in our history.  We must point out, however, that while we may speak of the total energy released by the impact, the effect of that impact depend greatly on the way the energy was released. As we shall explain later, the huge amount of energy released by the planetesimal was far more diffuse than, and so quite unlike, a nuclear explosion.

Nevertheless, the scene we describe is so far removed from anything that has been experienced by human beings, so far removed even from an phenomena contrived in laboratories, that we can do no more than speculate about the physical, chemical, and biological implications. What we or any others say or write about the detail of the event must contain a very large amount of informed guesswork.

There is one particular natural disaster that happened about a century ago and that is well documented. The eruption of the volcano Krakatoa, in what is now Indonesia, on August 27, 1883, is said to have been the most violent volcanic eruption ever recorded and perhaps the worst disaster of its kind in recorded history.  The tsunamis ("tidal" waves) alone killed some 36,000 people on the neighboring islands of Sumatra and Java. Probably Krakatoa exploded with the energy of something like 1,000 million tons of TNT. Our planetesimal impact released energy equivalent to about 100,000 Krakatoa-sized eruptions.