If you were to take a map of the world, cut out all the continents and lay them on a table, you might notice they can almost be put together like the pieces of a puzzle. Geologists believe the pieces of earth's outer shell---or tectonic plates---have always been on the move, continually bringing some continents together while splitting others apart every few hundred million years. While this process has clearly affected the evolution of the planet, what might not be as obvious is the effect it's had on the evolution of life.
Scientists believe species evolve to adapt to their environments. For example, whales have undeveloped leg bones inside them, which leads scientists to suspect they once walked on land. As the diets of these air-breathing mammals shifted to mostly plankton and other small ocean creatures, they began spending more and more time in the water until it finally became their home. Because having legs didn't do much in the way of giving whales an advantage over oceanic predators, they began evolving with each generation until finally --- millions of years later --- their legs had been replaced by fins. For similar reasons, giraffes developed long necks, polar bears developed thick coats and human beings began walking upright.
Adapting to Change
While whales evolved because they were forced to spend more time in the ocean to survive, other species had even less choice in the matter. When plate tectonics bring together previously separated landmasses, animals are forced to live in new environments and contend with new enemies. Evolution is nature's way of giving each species a chance to survive, gradually changing it to adapt to its environment. A prime example of this occurred about 55 million years ago, when geologists believe India and China came together, giving rise to the Himalayan-Tibetan plateau. At the time, one species of frog is believed to have lived in Asia; but when it was separated into different groups by the Himalayan-Tibetan plateau, each group began evolving independently, resulting in four different species.
Negative Effects of Plate Tectonics
Oftentimes, when earth's constantly changing layout leaves species in particularly hostile environments, they don't evolve quickly enough to survive. Such was the case about three million years ago, when volcanic activity formed a land bridge connecting North and South America. Animals from North America adapted so well to the southern continent that at least four native South American land mammals were driven to extinction. Other South American species, like the armadillo and the opossum, managed to escape to North America, becoming extinct in their native land but thriving in their new home. Meanwhile, a few northern species, like the llama and the tapir, disappeared from their homeland but began to thrive in South America.
Looking Into the Future
Because both processes occur over long stretches of time, the effects of evolution and plate tectonics might not be obvious --- but each continues to be an ongoing process. Over the course of the next 50 million years, Africa and Europe will come together, eliminating the Mediterranean Sea. In 250 million years, geologists believe, earth will be comprised of only two landmasses: a union of Antarctica and Australia and a combination of North America, South America, Europe, Asia and Africa. While scientists may be able to predict these changes millions of years in advance, only after the mergers occur will we know how evolution will react to them.
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