(Adapted from a permanent multimedia exhibit I wrote and produced for the Malaysian Ministry of Science's National Planetarium in Kuala Lumpur, under the supervision of  astrophysicist Dr. Mazlan Othman who now heads the United Nations Office for Outer Space Affairs in Vienna.) For millions of years, gigantic reptiles ruled the third planet from the Sun -– our home, the Earth. With each stride, the ground shook beneath their feet. The swampy air was filled with their monstrous trumpeting and reptilian cries. And then suddenly, mysteriously, the Age of Reptiles ended. Why? In search of an answer, the story of the dinosaurs will take us on a journey deep within the crust of the Earth and far, far into outer space.

Dinosaurs appeared 225 million years ago. It was during the Triassic period, when all the continents were joined together in a supercontinent called Pangaea. The climate was hot and swampy, just the way the dinosaurs liked it. Being cold-blooded creatures, they needed high temperatures to warm their blood. They flourished through the Jurassic period and on in to the Cretaceous, evolving from turkey-sized Thecodonts to the largest animals ever to live on land. And then, around 65 million years ago, they disappeared from the face of the Earth. Why did they all vanish at the very same time?

Extinction is an integral part of nature, making way for more viable life forms. Several mass extinctions have occurred over the ages, but even so, scientists can only guess at their causes. Perhaps the dinosaurs were affected by a climate change, when the continents began to break apart and drift toward the North and South Poles. Cooler temperatures would have made them sluggish and less able to hunt for food. A new climate would have changed the whole ecology of the Earth, like bringing new plants which might have been poisonous to the dinosaurs. Plankton, the simple sea organism which use the Sun’s energy to produce oxygen, are known to have become extinct at the beginning of the Cretaceous period. Maybe the dinosaurs had trouble breathing in this new environment.

Or, perhaps the answer is not on land or sea. Perhaps it is not even here on Earth. Since the beginning of mankind, we have gazed at the heavens, looking for answers. Prehistoric man noticed that certain celestial bodies move in orderly and predictable paths, and astronomy (the study of the stars) was born. Although an ancient science, it continues to yield new discoveries.

One astronomic explanation is that a star in a nearby constellation exploded, creating a supernova. This would have bathed the Earth in deadly cosmic rays.

Another theory is that the impact of a giant meteor striking the Earth could have caused the sudden extinction. Meteorites, which are space rocks, orbit millions of kilometers from Earth. A planet’s gravitational force might alter their usual path. Enormous craters are proof that meteors have struck the Earth in the distant past, sending dust and debris into the atmosphere. This would have blotted out the Sun’s rays, dropping temperatures and killing plants and animals alike. Or, asteroids, minor planets, could similarly strike the Earth when knocked out of the asteroid belt that orbits the Sun.

It could have been a comet. Mostly dust and ice with a sprinkling of rocky and metallic materials, comets orbit outside the solar system in the Oort Cloud. When a comet comes close to the Sun, the ice evaporates and forms a tail containing ash and gases. Some tails are up to 150 million kilometers long. The Dutch astronomer who gave his name to the Oort Cloud, Jan Oort, thought a comet was responsible for the dinosaur extinction. Oort thought comets entered the inner solar system when disturbed the gravitational force of a nearby star.

What star could disturb the comets? One is Nemesis, the Death Star. A faint red star, it is believed to be the Sun’s companion star even though it exists outside our solar system. Moving in an elliptical orbit, when it approaches the Sun it passes through the Oort Cloud, hurling comets toward Earth. If Nemesis orbits every 26 million years, then perhaps it is the cause of the regular mass extinctions on Earth.

Or maybe the cause is Planet X. Planet X is a tenth planet that may exist on the outer reaches of the Milky Way. When the Sun orbits the galaxy every 33 million years, it oscillates up and down. This may cause far off Planet X to disturb the Oort Cloud with each oscillation, heightening the probability of cometary disaster here on Earth.

So far the strongest proof that the dinosaur extinction was caused by something from outer space lies deep in the Earth’s crust. Geology, the study of Earth’s history, may offer an answer. Every layer of the Earth represents a period of time, and holds clues to the events of that age. American geologist Walter Alvarez noticed that there was an unexpected presence of iridium in the same layer, all over the world. The rare metal, from the Latin word meaning “rainbow”, appeared in the layer that represented a time 65 million years ago. That was when the dinosaurs became extinct.

Walter’s father was a Nobel Prize-winning physicist named Luis Alvarez. Walter told his father about the iridium, and the physicist theorized that it came from outer space, since space rocks are full of the metal and earth rocks are not. An explosion would have cast the iridium into the stratosphere, allowing it to settle on Earth in the consistent layer Walter Alvarez discovered. It might have been a meteor, or the collision of a comet, which is more common. Finally, we have solid evidence that the extinction of the dinosaurs has an astronomic cause.