Blobs of hot, dense material that curl around Earth’s core are much more widespread than previous research suggests.
A new method of analysing earthquake data has found even more of the previously detected continent-sized zones at the boundary between the planet’s core and mantle.
We still don’t know what these blobs are – they could be magma, molten iron leaking from the core, or something else – but with a more complete, detailed map of where they are, we can better understand the geological processes occurring deep inside Earth’s interior.
The core boundary lies some 2,900 kilometres (1,800 miles) below Earth’s surface. That’s extremely out of reach, so if we want to know what conditions are like down there, we have to get creative. Luckily, Earth comes with a built-in tool for probing its own guts: earthquakes.
The way quakes and tremors propagate through different kinds of material inside the planet has allowed seismologists to reconstruct and map the composition of Earth’s interior.
This is how vast blobs of super-hot material were identified at the core-mantle boundary, decades ago.
Because the heat causes greater degrees of melting, these zones slow velocity of the earthquake waves right down, so they’re known as ultra low velocity zones.
But earthquakes can be an unsatisfactory tool, providing only trickles of information at a time. You have to wait for earthquakes; each earthquake only probes a narrow zone; and weaker signals can get lost in the broader noise.