Scientists have discovered a new layer of partly molten rock under the Earth’s crust that might help settle a long-standing debate about how tectonic plates move.
- The research related to this discovery was published Feb. 6, 2023, in the journal Nature Geoscience.
Key findings
- As per the research paper, the melted rock is in the asthenosphere, the upper layer of the mantle that sits between about 50 miles (80 km) and 124 miles (200 km) below Earth’s surface.
- The mantle is a 2,900 km thick layer of solid rock sandwiched between the Earth’s upper crust and lower core.
- The mantle makes up the largest part of Earth. The asthenosphere is important for plate tectonics because it forms a relatively soft boundary that lets tectonic plates move through the mantle.
- The reasons why it is soft, however, are not well understood. Scientists previously thought that molten rocks might be a factor. The only way to peer into this layer of the mantle is with seismic waves from earthquakes.
- Researchers can detect the waves at seismic stations set up around the world, looking for subtle changes in the waveforms that indicate what kinds of materials the waves traveled through.
- Researchers collected data from thousands of seismic waves detected at 716 stations around the world.
- They found that rather than holding small areas of melt, the asthenosphere appears to contain a partially melted layer that extends around the globe, under at least 44% of the planet.
- The new study also shows that melt, in fact, does not appear to notably influence the flow of mantle rocks.
- According to the research, the convection of heat and rock in the mantle are the prevailing influence on the motion of the plates. Although the Earth’s interior is largely solid, over long periods of time, rocks can shift and flow like honey.
The Earth’s interior
- Core, mantle and crust are the three main concentric layers of the earth’s interior.
- The innermost layer surrounding the earth’s centre is called core, which is about 3500 kms in radius. Core is the most dense layer of the earth with its density range from 9.5 to 14.5 and sometimes even higher. It is composed mainly of the iron and nickel thus commonly known as Nife (Nickel+Ferrum). Core consists of two sub-layers. The inner one is solid and the outer one is semiliquid.
- The layer surrounding the core is known as mantle, a rock shell about 2900 kms thick and is composed of basic silicates. Major constituent elements of mantle are magnesium and silicon, hence, this layer is termed as Sima (Silica+Magnesium). The density of this layer varies from 3.3 to 5.7.
- Mantle is surrounded by the outermost layer of the earth, known as lithosphere and its density varies from 2.70 to 2.95. Major constituent elements of lithosphere are silica (Si) and aluminium (Al), thus this layer is termed as Sial (Silica+Aluminium). The outermost part of the lithosphere in known as crust, normally about 8 to 40 kms thick.
