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THE NEWS

Using data from one of the biggest earthquakes on records, scientists have discovered massive mountains in the Earth’s mantle, an advance that may change our understanding of how the planet was formed.

JOURNEY TO THE CENTRE OF THE EARTH:

  • Geophysicists from the Chinese Academy of Sciences and Princeton University in the United States used the echoes of a massive earthquake that struck Bolivia to piece together the topography deep beneath the surface.
  • To peer deep into the Earth, scientists used the most powerful waves on the planet, which are generated by massive earthquakes.
  • Data from earthquakes that are magnitude 7.0 or higher send out shockwaves in all the directions, that can travel through the core to the other side of the Earth and back again.
  • For this research, the key data came from waves picked up after a magnitude 8.2 earthquake that shook Bolivia in 1994, the second-largest deep earthquake ever recorded.
  • Scientists used powerful computers to simulate the complicated behaviour of scattering waves deep inside the Earth.
  • This technology depends on a fundamental property of waves, their ability to bend and also to bounce back, the earthquake waves travel straight through homogeneous rocks but reflect or refract when they encounter any boundary or roughness.

On 9 June 1994, an 8.2 magnitude earthquake rocked a populated region of the Amazon in the South America. Nothing this powerful earthquake had been seen in decades, with shocks being felt as far away as Canada. Not only it was big, but it was also deep, with a focal point estimated at a depth of just under 650 kilometres.

UNDERSTANDING EARTH’S INTERNAL GEOGRAPHY:

  • Our planet Earth is the third planet from the sun, after Mercury and Venus and before Mars.
  • It is about 150 million kilometres from the sun [this distance, called an astronomical unit (AU), is a standard unit of measurement in astronomy].
  • Earth’s interior is a very complex structure of superheated rocks. Most geologists recognize three major layers:
    • The dense core: The core is made of iron and nickel and it consists of a solid centre surrounded by an outer layer of liquid. The core is found about 2,900 kilometres below Earth’s surface and has a radius of about 3,485 kilometres.
    • The bulky mantle: Its mantle consists of heavy rock that surrounds the core. It is about 2,900 kilometres thick and makes up a whopping 84 percent of Earth’s total volume. Parts of the mantle are molten, meaning they are composed of partially melted rock. The mantle’s molten rock is constantly in motion. It is forced to the surface during volcanic eruptions and at mid-ocean ridges.
    • The brittle crust: The Earth’s crust is the planet’s thinnest layer, accounting for just 1 percent of its mass. There are two kinds of crust:
      • thin, dense oceanic crust and thick: Oceanic crust extends about 5 to 10 kilometres (3 to 6 miles) beneath the ocean floor
      • less-dense continental crust: Continental crust is about 35 to 70 kilometres (22 to 44 miles) thick.

DOES THE RESEARCH PROVE THE THEORY WRONG?

  • No. The explanation of the Earth’s interior is not wrong. The planet does leave out several other layers that scientists have identified within the Earth.

WHAT SCIENTISTS HAVE FOUND:

  • Scientists have used data from the earthquake to find mountains and other topography on a layer located at a boundary 410 miles (600 kilometres) straight down, which separates the upper and lower mantle.
  • In simpler words, stronger topography than the Rocky Mountains or the Appalachians is present at the 660-km boundary.
  • Lacking a formal name for this new founded layer, the researchers simply call it “the 660-km boundary.”
  • They are located at a boundary 600 kilometres straight down into the earth from the planet’s surface.

WHAT IT MEANS:

  • The presence of roughness on the “660-km boundary” has significant implications for understanding how the Earth was formed and continues to function.
  • The newly identified layer divides the mantle, into its upper and lower sections. For years, geoscientists have debated about the importance of the boundary.
  • In particular, scientists have studied how heat travels through the mantle, whether hot rocks are carried smoothly from the core-mantle boundary to the top of the mantle, or whether that transfer is interrupted at this layer.

Mantle knowledge:

  • Some mineralogical and geochemical evidence suggests that the upper and lower mantles are chemically different and that the two sections don’t mix thermally or physically.
  • While other findings suggest that there is no chemical difference between the two layers and called it a “well-mixed mantle,” with both the upper and lower mantle participating in the same heat-transfer cycle.
  • The recent findings provide insight into this question. The data suggest that both groups might be partially right.
  • The smoother areas of the new boundary could result from more thorough vertical mixing, while the rougher, mountainous areas may have formed where the upper and lower mantle don’t mix as well.

Heat trapped inside:

  • In addition, the roughness found in the structure, which existed at large, moderate and small levels, could theoretically be resulted due to heat anomalies or chemical heterogeneities.
  • But because of how heat is transported within the mantle, any small-scale thermal anomaly would be smoothed out within a few million years.
  • It leaves only chemical differences to explain the small-scale roughness.

Slabs of seafloor:

  • Geoscientists have long debated about the slabs of seafloor that get pushed into the mantle at subduction zones.
  • The findings suggest that remnants of these slabs may now be just above or just below the 660-km boundary.

HOW THE FINDINGS WILL HELP:

  • Deep understanding: These findings provide new information to understand the ancient tectonic plates which have now descended into the mantle, and where ancient mantle material might still reside deep inside the Earth.
  • A clear picture: Also, the discoveries permit the specialists to have a clearer knowledge into Earth’s tectonic plates and its mantles, just as painting a clearer picture of what the future holds.

IMPORTANT TERMS:

Seismic waves:

  • Seismic waves are vibrations or waves of energy generated by earthquakes. These waves travel through the Earth like the sound waves travel through the air.
  • The time it takes for seismic waves to arrive at seismic observatories allows scientists to locate the precise location of the earthquake that generated them.
  • There are two different categories of seismic waves:
    • Body wave: They travel through the interior of the Earth. They are further classified into two:
      • Primary waves (P-waves, or pressure waves): They are compression waves. They can propagate in solid or liquid material.
      • Secondary waves (S-waves, or shear waves): These are shear waves. They only propagate in solid material.
  • Surface wave: They propagate only at the interface between two different media, like the interface between Earth and atmosphere

Topography:

  • Topography is generally a term used to describe the detailed study of the Earth’s surface.
  • It includes changes in the surface such as mountains and valleys as well as features such as rivers and roads.
  • Not only Earth, but it can also include the surface of other planets, the moon, asteroids and meteors.

CONCLUSION:

Though the surface of the Earth is a bumpy place, with terrain made up of smooth ocean floors to jagged mountain peaks and everything in between, the landscape inside the Earth’s mantle is more complex. The study can tell us a lot about the Earth’s formation and how heat and material can travel through the Earth’s its different layers. But still no one exactly knows how these huge mountain structures may have evolved, but it is likely a result of movement of chemical mixing and material between the layers.

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