The Earth was born around 4.6 billion years ago, after which it has continued to evolve for a considerable length of time. Based on evidence found in rock formations, it is thought that by 4.4 billion years ago oceans and continents had already formed.
Research into such things as plate tectonics and plume tectonics (see Part 4: Earthquakes around the world) have advanced to the stage where it is has been concluded that from around two billion years ago, so-called supercontinents containing all the present-day continents were forming every 400-500 million years.
Recent studies have revealed quite a lot of detail about the formation and breaking up of these supercontinents up to around 600 million years ago. This is due to advances in a field of study known as paleomagnetism, which involves looking into the extent of continental drift by searching for rock formations that contain records of the Earth's magnetic field over time and then measuring the ages of these rock formations. The images used in this edition of Earthrium were provided by Dr. Ronald Blakey, a geologist at Northern Arizona University.
Well then, just what kind of supercontinents existed on Earth all those years ago? The following is a brief description of the supercontinents we currently know existed.
Neuna
Neuna was the Earth's first supercontinent and was formed around 1.9 billion years ago. We know that it broke up soon after it formed, but it is difficult to determine what form it took. The name Neuna was given to the continent by the Harvard University geologist Dr. Paul Hoffman, and is an acronym that derives from Northern Europe and North America. Traces of the orogenic activity of 1.9 billion years ago can still be found in various locations around the world, and on the basis of these it is thought that most of the landmass that currently makes up the continent of North America was once part of the Neuna supercontinent.
Rodinia
This supercontinent is thought to have existed from between one billion and 700 million years ago. It is now thought that before it started breaking apart, there was a major ice age that froze the entire surface of the Earth, including the ocean in the vicinity of the equator. Because when viewed from space the Earth would probably have resembled a huge lump of white snow, this theory has been labeled the Snowball Earth hypothesis.
According to one theory, during the Neuna and Rodinia periods there existed another supercontinent known as Colombia (1.5 billion years ago), although at this stage little is known about this supercontinent.
Gondwana
Gondwana was a new supercontinent that formed after Rodinia broke up. Most of it is thought to have been located in the southern hemisphere. If you click on "600 million years ago" at the bottom of the globe at left you'll notice a large continent in the form of a single landmass in the southern hemisphere. The supercontinent of Gondwana included the present-day continents of Africa, South America, Australia, and Antarctica, as well as the Indian subcontinent.
Pangaea
The supercontinent of Pangaea formed around 290 million years ago. It began to break apart some 250 million years ago, eventually separating into the six continents that exist today. Two hundred and fifty million years ago was also when the Earth's most severe extinction event occurred. It is thought that this extinction event is probably closely related to the break up of Pangaea, and extensive research is currently being carried out around the world to determine the exact relationship between the two events.
Supercontinents of the future
We know that at present the continents are all drifting in the direction of Asia. If this trend continues, the first thing that will happen, some 50 million years from now, is that Australia will collide with the Japanese archipelago. Next, some 200 to 300 million years in the future according to one theory, Africa and the Arabian peninsula, and then America will merge with Asia, possibly forming a single supercontinent known as Amasia.
From Seimei to chikyu no rekishi (History of life and the Earth) by Shigenori Maruyama and Yukio Isozaki (Iwanami Shoten)Although the speed at which the continents are moving is less than 1cm a year, by compressing time we hope we have brought home the fact that the Earth is a planet on which the landmasses are continually shifting.