• continental drift
    Continental drift is pushing Europe and North America apart, and Asia and the Indian subcontinent together.

    Map courtesy of CR Scotese, PALEOMAP Project

    Drifting Explanation
    Although Alfred Wegener identified the process of continental drift in 1912, he was unable to explain how it worked. Wegener suggested that perhaps the rotation of the Earth caused the continents to shift towards and apart from each other. (It doesn't.)

    The process of subduction, where heavier tectonic plates sink beneath lighter ones, was not well-established until the 1960s. Subduction is the main geologic force behind continental drift.

    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.

    In the early 20th century, German scientist Alfred Wegener published a book explaining his theory that the continental landmasses, far from being immovable, were drifting across the Earth. He called this movement continental drift.

    Wegener noticed that the coasts of western Africa and eastern South America looked like the edges of interlocking pieces of a jigsaw puzzle. He was not the first to notice this, but he was the first to formally present evidence suggesting that the two continents had once been connected.

    Wegener was convinced that the two continents were once part of an enormous, single landmass that had split apart. He knew that the two areas had many geological and biological similarities. 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 believed that all the continents—not just Africa and South America—had once been joined in a single supercontinent. This huge ancient landmass is known as Pangaea, which means “all lands” in Greek. 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 present positions as the continents.

    Tectonic Activity

    At first, other scientists did not accept Wegener’s theory of continental drift. But scientists now 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. Over time, tectonic activity changes the Earth’s surface, rearranging and reshaping its landmasses.

    Today, scientists believe 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.

    The continents are still moving today. Underwater exploration has revealed seafloor spreading. Seafloor spreading is the process of new crust forming between two plates that are moving apart. Along a network of mountain ranges in the ocean, molten rock rises from within the Earth and adds new seafloor to the edges of the old. As the seafloor grows wider, the continents on opposite sides of the ridges move away from each other.

    North America and Europe, for example, are moving away from each other at the rate of about 2.5 centimeters (1 inch) per year. If you could visit the planet in the future, you might find part of California separated from North America, becoming an island in the Pacific Ocean. Africa will eventually split in two along the Great Rift Valley. It is even possible that another supercontinent may form someday.

  • Term Part of Speech Definition Encyclopedic Entry
    Alfred Wegener Noun

    (1880-1930) German meteorologist and geologist.

    ancient Adjective

    very old.

    biological Adjective

    having to do with the study of life and living organisms.

    coast Noun

    edge of land along the sea or other large body of water.

    Encyclopedic Entry: coast
    continent Noun

    one of the seven main land masses on Earth.

    Encyclopedic Entry: continent
    continental drift Noun

    the movement of continents resulting from the motion of tectonic plates.

    Encyclopedic Entry: continental drift
    crust Noun

    rocky outermost layer of Earth or other planet.

    Encyclopedic Entry: crust
    fossil Noun

    remnant, impression, or trace of an ancient organism.

    Encyclopedic Entry: fossil
    geologic Adjective

    having to do with the physical formations of the Earth.

    Great Rift Valley system Noun

    series of faults and other sites of tectonic activity stretching from southwestern Asia to the Horn of Africa.

    habitat Noun

    environment where an organism lives throughout the year or for shorter periods of time.

    Encyclopedic Entry: habitat
    immovable Adjective

    unable to change position or move.

    island Noun

    body of land surrounded by water.

    Encyclopedic Entry: island
    jigsaw puzzle Noun

    interlocking pieces that, when correctly put together, display a picture or design.

    landmass Noun

    large area of land.

    mesosaurus Noun

    freshwater reptile that lived during the early Permian period, about 300 million years ago.

    molten Adjective

    solid material turned to liquid by heat.

    mountain range Noun

    series or chain of mountains that are close together.

    Pangaea Noun

    supercontinent of all the Earth's landmass that existed about 250 million years ago.

    Pannotia Noun

    supercontinent that existed about 600 million years ago.

    plate tectonics Noun

    movement and interaction of the Earth's plates.

    reptile Noun

    animal that breathes air and usually has scales.

    revolutionary Adjective

    new or innovative.

    rift valley Noun

    depression in the ground caused by the Earth's crust spreading apart.

    Encyclopedic Entry: rift valley
    Rodinia Noun

    supercontinent that existed about a billion years ago.

    seafloor spreading Noun

    rift in underwater mountain range where new oceanic crust is formed.

    Encyclopedic Entry: seafloor spreading
    supercontinent Noun

    ancient, giant landmass that split apart to form all the continents we know today.

    tectonic plate Noun

    large, moveable segment of the Earth's crust.

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