The dinosaurs downfall it came from outer space
How and why did the dinosaurs pass from Earth? Since British scientist Richard Owen coined the term which means “terrible lizard”—in 1842, scientists have struggled to explain the sudden demise of the creatures. For some i6o million years, they were the dominant life-form on the planet, the apex of the animal kingdom. Yet their story, preserved in an extensive fossil record, comes to an abrupt end around 65 million years ago. Their extinction, generations of scientists suspected, must have been due to some sort of cataclysmic natural disaster: a plague or worldwide drought, perhaps a drastic shift in Earth’s climate or atmosphere.
The answer to the mysterious demise of the dinosaurs emerged from one of the great unexplained events of the loth century. On June 30, 1908, something exploded near the Tunguska River in Siberia. Trees in a nine-mile radius from ground zero were incinerated; those in a 25-mile radius were felled —some 6o million of them. The blast occurred in such a remote region of Russia that it was not until 1927 that scientists mounted an expedition to explore it. They found that the ground near the blast crater contained high levels of iridium, a substance very rare on Earth but prevalent on asteroids. The even-tual conclusion: the Tunguska Event was caused when a meteorite at
least Zoo ft. in diameter exploded five miles above the ground. In 1980 physicist Luis Alvarez and his son Walter advanced a startling theory: perhaps a meteor impact similar to that at Tunguska had ended the age of the dinosaurs. The primary evidence: in soil core samples taken in locations all around the globe, iridium had been found in a thin layer of clay that formed the boundary between the fossil-rich rock of the Cretaceous period, the end of the dinosaur age, and the sparsely fossiled rock of the Tertiary period that followed. Alvarez’s hypothesis: a monster extraterrestrial body had slammed into the planet, sending an enormous fireball into the
stratosphere, along with vast amounts of debris. A great cloud of dust enshrouded Earth, blocking sunlight for months, even years. In the ensuing cold and dark, plants and animals perished. When the dust shroud eventually settled back to Earth, it formed the telltale worldwide layer of iridium in the clay. Some scientists scoffed. Then, in 1990, scientists realized a crater some 112 miles in diameter below the town of Chicxulub on the northern tip of Mexico’s Yucatan Peninsula, found in 1978, might be the culprit. The crater was dated at 65 million years old, strong evidence that the dinosaurs’ demise was caused by forces that came from beyond this world.
BIG BANG Above, this skull and neck of a -velociraptor were found in Mongolia. Right; an artist depicts a meteor striking the planet* The crater in the photocomposite at left is Meteor Crater in Arizona; it is 4,Ooo ft. in diameter and 57o ft. deep. In short: ouch!