University of Utah researchers found out that in the depths of Earth, there are enigmatic ultra-low velocity zones. They found out these zones are layered. Scientists think that these zones are leftovers of the processes that shaped our Earth. The research paper has been published in Nature Geoscience. National Science Foundation has funded this research.
Deep down in the mantle
We live on the crust of Earth. Between the crust and the centre of Earth, there is mantle. Mantle is made of solid rock but it can move the plate tectonics.
Scientists used Seismic waves to find out what is going on in the centre of Earth. These waves can flow through Earth after an earthquake. This way scientists can measure when these waves are arriving at different monitoring stations of Earth. Then they back-calculate how the waves have reflected by various structures of Earth. This is how the scientists know the boundaries between crust and mantle.
Ultra-low velocity zones help scientists to find out what these layers are made of. Scientists first thought the mantle was partially melted. They thought these zones must be the “hot spot” volcanic regions.
But Australian National University, Arizona State University and University of Calgary scientists experimented with an alternate hypothesis. They explored if the ultra-low velocity zones are made of different rocks.
Scientists said the ultra-low velocity zones might be made of iron oxide. Iron oxide behaves as metal in the deep mantle. This influences the Earth’s magnetic field.
Reverse seismic waves
The scientists studiedultra-low velocity zones under Coral Sea between Australia and New Zealand. This is a good location as earthquake happens frequently in that area. This provides high-resolution seismic picture. These observations can provide more information about ultra-low velocity zones.
Scientists got seismic image from 1800 miles down of the crust and mantle. The picture is not conclusive as thick layer of low-velocity material reflects seismic waves.
This is why, the scientists used reverse-engineering method. The name of the method is “Bayesian inversion”. This is a mathematically robust model which helped the scientists to understand the mantle.
The scientists wanted to know if there are layers in the ultra-low velocity zones or not. The model suggested that there are layers. This also suggested how these zones came to be.
The origin of Earth
By layers scientists mean, dense iron was sinking in the core of the Earth and lighter minerals were floating up in the surface. Then another planet maybe the size of Mars must have slammed Earth. This process might have thrown debris into Earth’s orbit which produced moon. This event raised the temperature of Earth.
After the collision the magma ocean has been formed. The ocean cooled itself over the billion of years. The dense materials sunk in the bottom of the ocean and the lighter materials layered on the surface of the ocean.
Over these billion of years, the dense layer pushed into small patches and these are the layered ultra-low velocity zones of today.