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century； one approximately a hundred and fifty feet in diameter strikes Earth； such as the one that produced the crater in Window； Arizona； and the other that exploded before impact in Siberia in 1908 that plastered eight hundred square miles。 Once every million years； an asteroid half a mile wide strikes with a force equal to detonating every nuclear device on Earth simultaneously。 Over two thousand of these big celestial missiles cross our orbit on a regular schedule。〃
〃Not a pretty picture；〃 said Pat。
〃Don't lose any sleep over it；〃 Friend said； smiling。 〃Your odds of dying from an asteroid are twenty thousand to one during your lifetime。 We can't； however； discount the logical possibility that it's only a question of time before our luck runs out。〃
Pitt poured a cup of coffee。 〃I assume you're talking about a really stupendous bang。〃
〃Indeed；〃 said Friend； nodding vigorously。 〃Once every one hundred million years； a mammoth asteroid or et strikes Earth； like the one that smacked into the sea off Yucatan sixty…five million years ago and caused the extinction of the dinosaurs。 This impact came from an object six miles in diameter that left a crater one hundred and twenty miles wide。〃
Friend paused to scan his paperwork before continuing。 〃That was smaller than the one that struck nine thousand years ago。 Our puter model indicates that it measured nearly ten miles in diameter and plunged into Hudson Bay； Canada。 The resulting chain reaction annihilated nearly ninety…nine percent of all plant and animal life on the planet； which is twenty percent more than the asteroid that caused the extinction of the dinosaurs sixty…five million years earlier。〃
Loren stared at Friend with rapt interest。 〃A chain reaction prising what type of disasters？〃
〃You take an object ten miles in diameter； weighing several billion tons； and then hurl it through a vacuum into a big soft ball at a speed of one hundred and thirty thousand miles an hour； and you're going to have a blast that is gargantuan beyond prehension。 The earth probably rang like a bell； as the shock of impact was transmitted into every corner。 Using puter simulation and visualization techniques； which were very plicated and would take me two hours to explain； we determined that the et came on an angle； punching into the southeastern section of Hudson Bay and blasting out a crater two hundred and thirty miles in diameter； or more than twice the size of the island of Hawaii。 The entire mass of water in the bay was vaporized； as the bulk of the now…disintegrating et plowed into the Earth to a depth of two miles。 Astronauts have taken photos that show a perfect sphere where the shoreline circles the remains of the crater。〃
〃How do you know it was a et and not an asteroid or meteor？〃 asked Yaeger。
〃An asteroid is a small body or minor planet that wanders the inner solar system and revolves around the sun。 Some are rich in carbon。 Others contain minerals rich in iron； silicon； and other minerals。 Meteorites for the most part； are smaller fragments from asteroids that have collided with one another and broken up。 The largest ever found weighed seventy tons。 A et is quite different。 It's often called a dirty snowball made up of ice； gas； and rocky dust particles。 They usually travel in very long oval orbits on the outer edge of the solar system； and often beyond。 Because of gravitational interaction from the sun and planets； a few are diverted and orbit around the sun。 When they e close to the sun； the et's surface ice vaporizes and forms a spectacular elongated cone or tail。 It's generally thought that they are leftovers from the formation of the planets。 By drilling and then analyzing the position of the microscopic debris found in and around the Hudson Bay crater； geophysicists discovered tiny particles that they identified as part of the et that slammed into the earth in seven thousand B。C。 Tests revealed no traces of the usual minerals and metals associated with asteroids。〃
〃So we have impact；〃 said Sandecker。 〃Then what happened？〃
〃A measureless inverted cone of red…hot rock； steam； dust； and debris was hurled up and above the atmosphere； only to plunge in a fiery rain back down on Earth； igniting uncontrollable forest fires around the world。 Huge amounts of sulfur； shock…heated nitrogen； and great doses of fluorides were injected into the atmosphere。 The ozone layer would have been destroyed； skies blotted out； as winds of hurricane strength whipped across the land and seas。 Our simulation suggests this cloud of debris and smoke lasted no less than fourteen months。 This alone would have killed off most of Earth's life and collapsed the food chain。〃
〃It sounds too horrible for me to imagine；〃 said Loren quietly。
Friend made a taut smile。 〃Lamentably； that's only the opening act。 Because Hudson Bay opened into the Atlantic Ocean； waves as high as seven or eight miles were formed that burst across the lowlands。 Florida would have been totally inundated； along with most of the islands of the world。 Much of Europe and Africa saw waves surging hundreds of miles inland from their shorelines。 Because most of Australia's ancient inhabitants lived on or near the coasts； the continent would have suffered a ninety…nine…percent death rate within minutes。 Southeast Asia would have been buried under water。 Vast multitudes of sea life would have been carried far inland and left to die when the giant waves finally receded。 The chemical balance of the oceans was altered。 What the upheaval didn't kill in the oceans； the silt； mud； and debris would。
〃Shuddering from the et's impact； massive earthquakes far beyond the top end of the Richter scale forever changed the dimensions of the mountains； plains； and deserts。 Then volcanoes around the globe； dormant or active； erupted molten lava in great sheets as high as a mile stormed over whatever land wasn't submerged。 If an astronaut had flown to Mars before the cataclysm and returned two years later； he would not have been able to recognize the world； nor would anyone he knew or loved still be alive。 He could very well find himself the only man on Earth。〃
Pitt looked at the astronomer。 〃You don't paint a very pretty picture。〃
〃The aftermath was ghastly to behold。 Once the deluge waters retreated； boulders of every size and shape were dispersed throughout the landscape； where they still rest today and are a great puzzle to geologists； who otherwise can't explain how they came to be there。 Vast deposits of mangled trees； along with the bodies of animals and sea life carried far inland； were heaped in huge deposits。 These deposits can still be found in the frozen regions of the world； proving that they were hurled there by a giant cataclysm。 Huge bodies of water were trapped； and formed lakes。 In one known instance； the land strait that separated the Atlantic Ocean from the valley and rivers of the Mediterranean was swept away and the sea was formed。 Old glaciers melted； new ones were formed。 Tropical forests began to grow in mild climates that were once lashed by frigid winds and freezing temperatures。 The Gobi； Sahara； and Mojave regions； then tropical