Continental drift describes one of the earliest ways geologists thought continents moved over time. Today, the theory of continental drift has been replaced by the science of plate tectonics.
The theory of continental drift is most associated with the scientist Alfred Wegener. In the early 20th century, Wegener published a paper explaining his theory that the continental landmasses were “drifting” across the Earth, sometimes plowing through oceans and into each other. He called this movement continental drift.
Pangaea
Wegener was convinced that all of Earth’s continents were once part of an enormous, single landmass called Pangaea.
Wegener, trained as an astronomer, used biology, botany, and geology describe Pangaea and continental drift. For example, fossils of the ancient reptile mesosaurus are only found in southern Africa and South America. Mesosaurus, a freshwater reptile only one meter (3.3 feet) long, could not have swum the Atlantic Ocean. The presence of mesosaurus suggests a single habitat with many lakes and rivers.
Wegener also studied plant fossils from the frigid Arctic archipelago of Svalbard, Norway. These plants were not the hardy specimens adapted to survive in the Arctic climate. These fossils were of tropical plants, which are adapted to a much warmer, more humid environment. The presence of these fossils suggests Svalbard once had a tropical climate.
Finally, Wegener studied the stratigraphy of different rocks and mountain ranges. The east coast of South America and the west coast of Africa seem to fit together like pieces of a jigsaw puzzle, and Wegener discovered their rock layers “fit” just as clearly. South America and Africa were not the only continents with similar geology. Wegener discovered that the Appalachian Mountains of the eastern United States, for instance, were geologically related to the Caledonian Mountains of Scotland.
Pangaea existed about 240 million years ago. By about 200 million years ago, this supercontinent began breaking up. Over millions of years, Pangaea separated into pieces that moved away from one another. These pieces slowly assumed their positions as the continent we recognize today.
Today, scientists think that several supercontinents like Pangaea have formed and broken up over the course of the Earth’s lifespan. These include Pannotia, which formed about 600 million years ago, and Rodinia, which existed more than a billion years ago.
Tectonic Activity
Scientists did not accept Wegener’s theory of continental drift. One of the elements lacking in the theory was the mechanism for how it works—why did the continents drift and what patterns did they follow? Wegener suggested that perhaps the rotation of the Earth caused the continents to shift towards and apart from each other. (It doesn't.)
Today, we know that the continents rest on massive slabs of rock called tectonic plates. The plates are always moving and interacting in a process called plate tectonics.
The continents are still moving today. Some of the most dynamic sites of tectonic activity are seafloor spreading zones and giant rift valleys.
In the process of seafloor spreading, molten rock rises from within the Earth and adds new seafloor (oceanic crust) to the edges of the old. Seafloor spreading is most dynamic along giant underwater mountain ranges known as mid-ocean ridges. As the seafloor grows wider, the continents on opposite sides of the ridge move away from each other. The North American and Eurasian tectonic plates, for example, are separated by the Mid-Atlantic Ridge. The two continents are moving away from each other at the rate of about 2.5 centimeters (1 inch) per year.
Rift valleys are sites where a continental landmass is ripping itself apart. Africa, for example, will eventually split along the Great Rift Valley system. What is now a single continent will emerge as two—one on the African plate and the other on the smaller Somali plate. The new Somali continent will be mostly oceanic, with the Horn of Africa and Madagascar its largest landmasses.
The processes of seafloor spreading, rift valley formation, and subduction (where heavier tectonic plates sink beneath lighter ones) were not well-established until the 1960s. These processes were the main geologic forces behind what Wegener recognized as continental drift.

The way some continents fit together like puzzle pieces inspired the theory of continental drift.
Map by USGS
Colliding Skyward
The collision of the Indian subcontinent and Asian continent created the Himalayan mountain range, home to the world's highest mountain peaks, including 30 that exceed 7300 meters (24,000 feet). Because continental drift is still pushing India into Asia, the Himalayas are still growing.
Urkontinent
Alfred Wegener’s original name for his proposed, ancient continent was “Urkontinent”—ur meaning “first or original,” and kontinent meaning “continent” in Wegener’s native language, German. A more popular name for this huge ancient landmass is Pangaea, which means “all lands” in Greek.
adapt
Verb
to adjust to new surroundings or a new situation.
Alfred Wegener
Noun
(1880-1930) German meteorologist and geologist.
ancient
Adjective
very old.
astronomer
Noun
person who studies space and the universe beyond Earth's atmosphere.
biology
Noun
study of living things.
botany
Noun
study of plants.
climate
Noun
all weather conditions for a given location over a period of time.
dynamic
Adjective
always changing or in motion.
enormous
Adjective
very large.
freshwater
Adjective
having to do with a habitat or ecosystem of a lake, river, or spring.
frigid
Adjective
very cold.
geologist
Noun
person who studies the physical formations of the Earth.
geology
Noun
study of the physical history of the Earth, its composition, its structure, and the processes that form and change it.
Great Rift Valley system
Noun
series of faults and other sites of tectonic activity stretching from southwestern Asia to the Horn of Africa.
Noun
environment where an organism lives throughout the year or for shorter periods of time.
hardy
Adjective
strong or able to withstand severe weather.
humid
Adjective
air containing a large amount of water vapor.
jigsaw puzzle
Noun
interlocking pieces that, when correctly put together, display a picture or design.
landmass
Noun
large area of land.
massive
Adjective
very large or heavy.
mechanism
Noun
process or assembly that performs a function.
mesosaurus
Noun
freshwater reptile that lived during the early Permian period, about 300 million years ago.
Mid-Atlantic Ridge
Noun
underwater mountain range that runs from Iceland to Antarctica.
mid-ocean ridge
Noun
underwater mountain range.
molten
Adjective
solid material turned to liquid by heat.
mountain range
Noun
series or chain of mountains that are close together.
oceanic crust
Noun
thin layer of the Earth that sits beneath ocean basins.
Pangaea
Noun
supercontinent of all the Earth's landmass that existed about 250 million years ago.
reptile
Noun
animal that breathes air and usually has scales.
slab
Noun
flat, thick piece of material such as earth or stone.
specimen
Noun
individual organism that is a typical example of its classification.
stratigraphy
Noun
study of rock layers and layering.
subduction
Noun
process of one tectonic plate melting, sliding, or falling beneath another.
supercontinent
Noun
ancient, giant landmass that split apart to form all the continents we know today.
tectonic plate
Noun
massive slab of solid rock made up of Earth's lithosphere (crust and upper mantle). Also called lithospheric plate.
tropical
Adjective
existing in the tropics, the latitudes between the Tropic of Cancer in the north and the Tropic of Capricorn in the south.
tropical climate
Noun
climate group that experiences hot, wet summers.
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