The land masses of the Earth ride on thin crustal plates that float upon a sea of magma. Called "continental drift," a term coined by Alfred Wegener in 1912, this inexorable movement has inched its way over the billions of years to shape and reshape the continents into the formations we see today.
Beginnings
The nascent Earth, fresh from the high energy, high temperature bombardments of interstellar debris and flowing with currents of melted rock, was yet to see the first stirrings of life. As eons passed, the surface began to cool and congeal, sealing oceans of melted rock beneath its surface. Convection currents within the liquid interior moved the surface layer ceaselessly. Subsequent impacts from comets brought water to the planet and the stage was set for continent formation.
Plate Tectonics and Formation
The existence of the supercontinent Pangaea is a cornerstone of the science of plate tectonics. The geological processes that formulate the aggregation and fragmentation of land masses have governed the evolution of Earth's crust for billions of years. We have scientific evidence that the supercontinent of Pangaea was, in fact, formed about 300 million years ago--toward the beginning of the Permian Age, which lasted from 290 to 248 million years ago. The Permian Age was at the end of the Paleozoic Period, which lasted about 325 million years, from about 570 million years ago to about 248 million years ago. By this time the Earth itself was already well over four billion years old and life forms of many different species had a firm foothold on both the land and in the oceans.
Reconstruction
Less certain, and destined to remain so, is the number of times in the Earth's history that such supercontinents formed. The geological record for the past one billion years is sufficiently well researched and scientists have a good understanding of the changing positions of continents, but before that time the evidence necessary to make a determination has long ago eroded. It is known, however, that during the Paleozoic Period there were six major continental land masses. These land masses, which included the continents of Gondwana, Euramerica and Siberia, had once been part of a supercontinent know as Rodinia which, itself, broke up about 650 million years ago. It was these continents that came together during the Permian to form the supercontinent of Pangaea.
Break Up
Toward the middle of the Permian period, Pangaea began to split into two new continents which have been named Laurentia (comprising North America, Europe and Siberia) and Gondwanaland (comprising Asia, South America and Africa). During the mid-Jurassic Period, roughly 167 million years ago, Gondwanaland began to drift apart. During the Cretaceous Period, roughly 130 million years ago, South America began drifting from Africa, eventually joining the North American portion of Gondwanaland at the Isthmus of Panama. The result was the creation of the Atlantic Ocean. Elsewhere, the surface area of the Earth was occupied by a single large ocean, known as Panthalassa, and a much smaller sea to the east of Pangaea known as Tethys. In the interior, Pangaea was actually a collection of large islands, separated from each other by shallow continental seas.
Today
Fossil evidence proves that the land masses comprising today's continents shared many species of plants and animals despite their great distances from each other. This could only be the case if these land masses were at some point in their history joined together. Once the breakup of Pangaea began, the continents continued their relentless drifting in accordance with the subterranean convection currents. The process continues to this day and at some point in the distant future, the continents will once again be forced together and the process will repeat anew.
Tags: million years, land masses, about million, about million years, supercontinent Pangaea
