News Excerpt:

Scientists using an ocean drilling vessel have dug the deepest hole ever in rock from Earth’s mantle – penetrating 4,160 feet (1,268 meters) below the Atlantic seabed – and obtained a large sample that is offering clues about our planet’s most voluminous layer.

More about news:

• The mantle, comprising more than 80% of the planet’s volume, is a layer of silicate rock sandwiched between Earth’s outer crust and ferociously hot core. Mantle rocks generally are inaccessible except where they are exposed at locations of seafloor spreading between the slowly moving continent-sized plates that make up the planet’s surface.
• One such place is the Atlantis Massif, an underwater mountain where mantle rock is exposed on the seafloor. It is located in the middle of the Atlantic just west of the vast mid-Atlantic Ridge that forms the boundary between the North American plate and the Eurasian and African plates.
• This cylindrical core sample, researchers said, is providing insight into the composition of the upper part of the mantle and the chemical processes that occur when this rock interacts with seawater over a range of temperatures. Such processes may have underpinned the advent of life on Earth billions of years ago.
• Using equipment aboard the vessel JOIDES Resolution, the researchers drilled into mantle rock about 2,800 feet (850 meters) beneath the ocean surface from April to June 2023. The core sample they recovered comprises more than 70% of the rock – 2,907 feet (886 meters) in length – from the hole they drilled.
• The recovery is record-breaking in that previous attempts of drilling mantle rocks have been difficult, with penetration no deeper than 200 meters (656 feet) and with relatively low recovery of rocks. In contrast, researchers penetrated 1,268 meters, recovering large sections of continuous mantle rocks.
• The core sample has a diameter of about 2-1/2 inches (6.5 cm).
• The researchers added a reinforced concrete cylinder lining to the uppermost part of the hole and then drilled unexpectedly easily.
• The reaction between seawater and mantle rocks on or near the seafloor releases hydrogen, which in turn forms compounds such as methane, which underpin microbial life. This is one of the hypotheses for the origin of life on Earth.
• Recovery of mantle rocks enables us to study these reactions in great detail and across a range of temperatures, and link it to the observations our microbiologists make on the abundance and types of microbes present in the rocks, and the depth to which microbes occur beneath the ocean floor.
• The drill site was located close to the Lost City Hydrothermal Field, an area of hydrothermal vents on the seabed spurting super-heated water. The core sample is thought to be representative of the mantle rock beneath the Lost City vents.
• The core sample is still being analyzed. The researchers made some preliminary findings about its composition and documented a more extensive history of melting – molten rock – than expected.
• The mineral orthopyroxene in particular showed a wide range of abundance on a range of scales, from the centimeter to hundreds of meters.

About Structure of the Earth:

The earth’s radius is 6,370 km. No one can reach the centre of the earth and make observations or collect samples of the material. The earth is made up of three different layers: the crust, the mantle and the core.

• Crust:

• • It is the outermost solid part of the earth. 
  • It is brittle in nature. 
  • The thickness of the crust varies under the oceanic and continental areas. 
  • Oceanic crust is thinner as compared to the continental crust. 
  • The mean thickness of oceanic crust is 5 km whereas that of the continental is around 30 km. 
  • The continental crust is thicker in the areas of major mountain systems. 
  • It is as much as 70 km thick in the Himalayan region.
  • It is made up of heavier rocks having density of 3 g/cm3

• The Mantle:

• • The portion of the interior beyond the crust is called the mantle. 
  • The mantle extends from Moho’s discontinuity to a depth of 2,900 km. 
  • The upper portion of the mantle is called the asthenosphere. The word astheno means weak. It is considered to be extending up to 400 km. It is the main source of magma that finds its way to the surface during volcanic eruptions. 
  • It has a density higher than the crust’s (3.4 g/cm3).

• The Core:

• • As indicated earlier, the earthquake wave velocities helped in understanding the existence of the core of the earth. 

• • The core-mantle boundary is located at a depth of 2,900 km. 

• • The outer core is in liquid state while the inner core is in solid state. 

• • The density of material at the mantle core boundary is around 5 g/cm3 and at the center of the earth at 6,300 km, the density value is around 13g/cm3. 
  • The core is made up of very heavy material mostly composed of nickel and iron.