Amateur Astronomers Association of Princeton

by S. Prasad Ganti

Both children and adults alike are fascinated by dinosaurs, the supersized “terrible lizards” of the past. Although they became extinct long ago, imaginations were stoked when Michael Crichton brought them to life in his sci-fi novel “Jurassic Park”. Steven Spielberg brought those creatures to life when he made the novel into a movie. Dinosaurs lived long before human beings appeared on the earth hundreds of millions of years ago and perished about sixty-five million years ago. The movie “Jurassic Park” claimed to be sixty-five million years in the making! So, what caused the extinction of these species?

It was long postulated that the birds replaced dinosaurs. The missing link between the two seemingly dissimilar species was the discovery of skeletal pieces of Archaeopteryx. This creature looks partly like a bird and partly like a dinosaur. The evolution of birds from dinosaurs still does not explain the reason dinosaurs ceased to exist on planet earth. Understanding and investigating natural history is not easy. The further you go into the past, more the things become fuzzier. Only part of the artifacts may still be around. Newer techniques needed to be developed to date such fossils.

Related to the existence and extinction of species on earth has been the many changes that the Earth has undergone in about four billion years of its existence: starting off as a hot ball soon after the solar system was formed, cooling off, chemical changes, atmospheric changes, and the appearance of first signs of life as single-celled organisms about three billion years ago. Also important are collisions with other extraneous bodies like the asteroids which are remnants of the formation of our solar system.

The Cambrian explosion occurred around half a billion years ago when the number of species exploded all around the globe. This happened in the ladder of evolution after multicellular organisms appeared and introduction of sex had ensured variety and survivability of the offspring. The Cambrian explosion has nothing to do with any kind of physical detonation like a nuclear blast. Natural historians believe that there have been five mass extinctions to date since the Cambrian explosion. The last of which happened about sixty-five million years ago when the dinosaurs became the casualty. This last one has been investigated in detail, but the details on the ones before are only sketchy.

Enter the father-son duo of Luis Alvarez and Walter Alvarez. Luis is  the famous Nobel prize-winning physicist who travelled on the plane that trailed the Enola Gay when it dropped the first atom bomb on Hiroshima in the Second World War. His son Walter became a geologist. He discovered a peculiar layer of sixty-five million year old rock that which forms a distinct narrow. The layer contains iridium, a chemical element that is found in abundance in the asteroids. The same layer with very similar age was found in several parts of the world.

The father and son duo with a highly skeptical group of scientists developed  the idea that an asteroid came from the space to wipe out the dinosaurs on the earth. The size of the asteroid, the speed with which it burrowed into the earth and the aftermath of the explosion on the climate, including blocking of the sun and stopping most photosynthesis, were modeled in great detail. The earlier volcanic eruption at Krakatoa about a hundred years ago served as a backdrop for this study. The final nail in the coffin was the finding of the impact crater below the sea near the Yucatán peninsula in Mexico. This is where an asteroid, several miles across, came crashing down, caused a giant explosion and wiped out the giant species, along with others of varying sizes.

The establishment of this cause was a major triumph for the dinosaur detectives. The fact that climate change has happened in the past and asteroid collisions have been frequent, does remind us of the potential perils that can strike us. We cannot take the safety of our home planet for granted. Of course, there is no reason to despair either. We just need to be aware of history so that we are better prepared to deal with future disasters.