Orogeny ("mountain creating" in Greek) is a mountain-building event caused by extreme volcanism (as in the Deccan Traps) or movement of the tectonic plates, large slabs of rock that make up the Earth's crust. The plates float on top of a plastic, superheated mantle, made of partially melted rock. As the material in the mantle circulates, the tectonic plates slowly move around on top, creating different continental arrangements over tens or hundreds of millions of years.
At first, the entire Earth was molten, with a fairly uniform height, until large segments and eventually the entire planet cooled down and became solid, fragmenting into several distinct plates. Over three billion years ago, the first known orogeny events began, due to both volcanism and plate movement. The oceans already existed by this time, and may have formed only 100 million years after the formation of the Earth itself.
As of 2008, there is some confusion among geologists as to which continent was the first. Some assert that orogeny produced the first continent formed 3 billion years ago, which they call Ur. Ur forms parts of Africa, Australia, India, and Madagascar, and would have been slightly smaller than modern-day Australia. Others say the first continent formed 3.3 - 3.6 billion years ago, called Vaalbara, which is represented today by parts of Western Australia and South Africa. Whichever the first continent was, when it formed, it was probably the only portion of the Earth's crust poking out of the surface of the water. For hundreds of millions of years, the Earth may have been entirely covered by water.
Numerous orogeny events occurred thereafter, creating all the continents and mountains we know today. The continents are made up of the least dense rock in the Earth's crust, which is why they "float" at the top. Orogenies can be dated accurately because of radiometric dating of rocks around the world, in combination with knowledge of the Earth's tectonic plates and their divergent boundaries.
Dozens of orogenies are known. One of the most famous and recognizable is the Himalayan orogeny, which occurred around 55 million years ago, when the subcontinent of India collided with the Eurasian Plate while moving north. These two plates pressing together caused the creation of great mountain ranges at the boundary, known today as the Himalayas. The Himalayas include Mt. Everest, the tallest mountain on the planet.
Michael is a longtime WiseGEEK contributor who specializes in topics relating to paleontology, physics, biology, astronomy, chemistry, and futurism. In addition to being an avid blogger, Michael is particularly passionate about stem cell research, regenerative medicine, and life extension therapies. He has also worked for the Methuselah Foundation, the Singularity Institute for Artificial Intelligence, and the Lifeboat Foundation.