London: Scientists have made an advance in understanding the mysterious dents in our planet`s gravitational field.
On sailing towards the centre of the Indian Ocean and a loss in one`s weight is observed because here the Earth`s gravitational field is weaker.
Similar dents in field strength can be observed in the north-east Pacific Ocean and the Ross Sea.
These weaknesses are believed to be a product of "slab graveyards" - ancient pieces of crust and sediment that were pushed down into the Earth when plates collided and are now falling through the mantle.
Since the slabs are denser than the surrounding mantle, they tend to have a stronger gravitational pull.
But when they fall their effect on the gravitational field at the Earth`s surface lessens.
However, surrounding these areas are even weaker, unexplained dents in the field.
According to Sonja Spasojevic from the California Institute of Technology in Pasadena and colleagues, this could be because the movement of the slabs through the mantle forces plumes of less dense material to rise towards the surface.
They believe the distribution of the unexplained weak spots simply reflects the pattern of these plumes.
"The new explanation is plausible but there are other possibilities too," New Scientist quoted Norm Sleep a geophysicist at Stanford University in California, as saying.
The study has appeared in the journal Nature Geoscience.