Nancy Davis, age 10, of Delmar, New York, for her question:
What happened in the Cretaceous Period?
Scientists tell us that it is impossible to invent a time travel machine. Too bad. It would be great fun to journey back for a look at our world as it was. But patient experts have dug up the details and we can imagine the past scenery in our minds.
A week lasts only seven days, but it is hard to recall all the things that hap= pened since last Friday. In the past million years, 52 million weeks have gone by. And a million years is just a blink in the long story of our planet. The Cretaceous Period started about 130 million years ago. This page in the old earth's diary lasted through roughly 70 million years. To visit it, we would have to travel back in time through more than three billion weeks or 60 million years. Naturally there have been a lot of changes and we would expect the Cretaceous world to be very different from the modern world.
Take a deep breath, because those changes are more astonishing than you imagined. Even the world map is different. True, the Appalachian Mountains stand along the eastern part of our continent. But they are newer and much taller. The Sierra Nevada peaks in the West are so new that many of them are still steamy volcanos. The Rockies are young mountains beginning to push upward with the help of earthquakes and fiery volcanos. There are no steep sided Alps in Europe and no lofty Himalayas in Asia. The middle half of North America is not on the map because it happens to be taking a dunk under the sea.
It may take us a while to get used to the different geography. But there are bigger surprises to behold in the plants and animals that populate the strange Cretaceous world. Early in the period, the members of the bird world are gaaky, wide winged flying reptiles. The ancestors of our feathery song birds begAn arriving about 50 million years later. But our dogs and cats, our horses and camels, and most of our familiar everyday animals are nowhere to be found. Fot this is not the Age of Mammals.
The Cretaceous Period is the Age of Reptiles, the last chapter in their long reign that lasted more than 150 million years. There are monstrous dinosaurs that look like dragons and rhinos and armor plated tanks. Everywhere there are dinosaurs in assorted shapes and sizes. There are frogs and sizeable salamanders but almost all the animals of this period are reptile type dinosaurs, large and small. Some thrive in the sea and some in the weedy marshes. The world climate is warm and this word has no flowers or tender grasses. Some animals feed on the tough bushes or on the greenery of rangy trees. These vegetarians are devoured by their meat eating dinosaur relatives.
The Cretaceous Period ended with the most dramatic event in the long history of life on earth. Quite suddenly, all the dinosaurs, large and small, departed from the world forever. No one is quite sure why they failed to survive. There was a change in the world climate and perhaps the cold blooded reptiles were unable to cope with the weather. The grassy plants arrived to carpet the ground and crowded out many tough plants that the dinosaurs had eaten. Perhaps the teeth of the extinct reptiles could not cope with the new grassy vegetation.