Formation of Continents

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    In Context

    • According to a recent study published in Nature journal, giant meteorite impacts could be responsible for the formation of continents on Earth.

    More about the study

    • About:
      • According to the study, Earth’s continents were formed by massive meteorite impacts that were prevalent during the first billion years of our planet’s four and a half billion-year history.
      • Meteorite impacts generated massive energy to form oceanic plates, which later evolved into continents.
    • The process:
      • The giant meteorite hit Earth and melted the outer shell of the Earth or the lithosphere, according to the study.
      • This impact released the pressure on the underlying mantle. 
      • As a result, the mantle likely melted, creating an oceanic plateau.
    • Significance:
      • Earth is the only planet that is known to have continents
      • What amazes scientists is the evolution and formation of the continents, making it the most researched field amongst planetary scientists. 
      • First of its kind:
        • It is well known that numerous such impacts have hit the planet from archaic times.
        • This research provides the first solid evidence that the processes that ultimately formed the continents began with giant meteorite impacts, similar to those responsible for the extinction of the dinosaurs, but which occurred billions of years earlier.
      • Key to reserves of metals: 
        • Understanding the formation and evolution of continents is important as it is the key to reserves of metals such as lithium, tin and nickel, which are required to develop batteries, the study noted.
          • Shallow melting of the rocks separates the lower density elements, such as lithium, from the higher density ones, such as iron.
          • Eventually, the lower density elements rise to the surface as a granitic continental crust. 
    • Meteorites impact other planets too, so why is such a phenomenon exclusive to Earth?
      • Other rocky planets and the moon had little or no water by the time the flux of effects declined.

    About Impact event

    • An impact event is a collision between astronomical objects causing measurable effects. 
    • Impact events have physical consequences and have been found to regularly occur in planetary systems, though the most frequent involve asteroids, comets or meteoroids and have minimal effect
    • When large objects impact terrestrial planets such as the Earth, there can be significant physical and biospheric consequences, though atmospheres mitigate many surface impacts through atmospheric entry.
    • Major impact events have significantly shaped Earth’s history, having been implicated in the: 
      • Formation of the Earth–Moon system, 
      • The evolutionary history of life, 
      • The origin of water on Earth, and 
      • Several mass extinctions.

    Alternative theories of Continent formation

    • The most commonly accepted theory in place attributes continent formation to the movement of tectonic plates.
    • Earth is uncommon among the planets and also from our moon that its outer surface is divided into rigid slabs, which were called tectonic plates by Wegener in his theory. 
      • While their surfaces exhibit evidence of recent deformation, neither planet has a surface divided into plates.
    • As the technology advanced, making it possible for deeper exploration, the theories of continental drift and seafloor spreading got positive scientific data in support.
      • The two theories were merged to develop the modern plate tectonic theory.

     

    Plate Tectonic Theory/Plate Tectonic

    • This concept was formulated in the 1960s by Alfred Wegener. 
    • According to the theory, Earth has a rigid outer layer, known as the lithosphere, which is typically about 100 km (60 miles) thick and overlies a plastic (moldable, partially molten) layer called the asthenosphere
    • The lithosphere is broken up into:
      • seven very large continental- and ocean-sized plates,
      • six or seven medium-sized regional plates, and 
      • several small plates
    • These plates move relative to each other.
      • They typically move at rates of 5 to 10 cm (2 to 4 inches) per year, and interact along their boundaries.
      • They converge, diverge, or slip past one another. 
      • Mountain formation:
        • Plate motions cause mountains to rise where plates push together or converge. 
      • Ocean formation:
        • Continents fracture and oceans are formed where plates pull apart or diverge.
    • The continents are embedded in the plates and drift passively with them, which over millions of years results in significant changes in Earth’s geography.
    • Such interactions are thought to be responsible for most of Earth’s seismic and volcanic activity, although earthquakes and volcanoes can occur in plate interiors.
    • Evidence of Plate Tectonic Theory:
    • Continent Puzzle:
      • The continents fit together almost like puzzle pieces forming Pangaea (one super-continent).
    • Fossil evidence:
      • Fossils on different continents are similar to fossils on continents that were once connected.  
      • When the continents split, different life forms developed.
    • Distributions of rocks:
      • Most distributions of rocks within Earth’s crust, including minerals, fossil fuels, and energy resources, are a direct result of the history of plate motions and collisions and the corresponding changes in the configurations of the continents and ocean basins.

     

    Source: DTE