From Atlantis to El Dorado and Avalon, legend tells us that the Earth is littered with lost lands that once suffered a dramatic fall.
While these are widely regarded as inventive myths, a new study reveals evidence for ‘a lost world’ beneath the Pacific Ocean.
Scientists from ETH Zurich and the California Institute of Technology (Caltech) have found enormous structures deep beneath the waters of the Pacific Ocean that ‘shouldn’t exist’.
This mysterious material – which causes seismic waves in the region to behave strangely – could be evidence of a lost land from hundreds of millions of years ago.
According to current scientific theories, the anomalous material in the lower mantle, some 1,000 kilometers underwater, ‘should not be found there’.
The findings, described as a ‘great mystery’, challenge ‘our current understanding of how the Earth works’, according to researchers.
“Determining the Earth’s structure is of paramount importance to unravel its internal dynamics,” the team says in their paper, published in Scientific reports.
‘These findings suggest a more diverse origin for these anomalies in Earth’s lower mantle.’
Using a new model, researchers discover zones in Earth’s lower mantle where seismic waves travel slower (red) or faster (blue) – and cannot come from submerged plates. The large blue zone in the western Pacific Ocean (just above the center of the image) was previously unknown
From Atlantis to El Dorado and Avalon, legend tells us that the Earth is littered with lost lands that once met dramatic demise. Pictured: an image of Atlantis
The Earth consists of three layers: the crust, the mantle and the core, which was later separated into ‘inner’ and ‘outer’.
The problem is that no one can see into the Earth, and no one can drill deep enough to take rock samples from the Earth’s mantle.
Instead, scientists study the speeds of seismic waves – the vibrations caused by earthquakes and explosions – as they travel through the planet’s interior.
Seismographic stations record these waves and based on these recordings, experts can draw conclusions about the structure and composition of the Earth.
“This is very similar to the way doctors use ultrasound to image organs, muscles or veins in the body without opening it,” ETH Zurich said.
It is also known that Earth’s lithosphere – the rocky, outer shell, consisting of the upper part of the mantle and the crust – consists of about fifteen tectonic plates.
Seismic activity can be detected along tectonic plate boundaries, where the plates grind against each other.
But in the distant past, large plates have disappeared into the Earth’s mantle through ‘subduction’.
The Earth consists of three layers: the crust, the mantle and the core, which was later separated into ‘inner’ and ‘outer’. A recent study also suggested the existence of an ‘inner core’
The anomalous findings, described as a ‘great mystery’, challenge ‘our current understanding of how the Earth works’. In this image, A and B show the locations of seismic stations along the Pacific Ocean. C through F show the seismic wave anomalies in traditional map view and as a cross-section
This is the geological process in which an edge of one plate is pushed under the edge of another plate – and over time an entire plate can be lost.
In the past, seismologists have determined the position of subducted tectonic plates in the Earth’s mantle, but these have always been below subduction zones.
In the new study, researchers from ETH Zurich and Caltech used a computational technique called ‘full-waveform inversion’, which constructs a 3D image of the Earth using seismic wave data.
They identified areas beneath the Pacific Ocean that resemble remnants of subducted plates, but far away from plate boundaries with no geological evidence of past subduction.
The Pacific Ocean is one big plate, so there shouldn’t be any subduction material underneath it anyway.
This suggests that the anomalies are not lost subducted plates. However, what the material is instead – or what it means for Earth’s internal dynamics – is a mystery.
“It’s like a doctor who has been examining blood circulation with ultrasound for decades and finds arteries exactly where he expects them,” says co-author Professor Andreas Fichtner, a seismologist at ETH Zurich.
Seismic activity can be detected along tectonic plate boundaries, where the plates grind against each other. But in the distant past, large plates have disappeared into the Earth’s mantle through ‘subduction’
The Pacific Ocean is one big plate, so there shouldn’t be any subduction material underneath it. Plate boundaries are shown here in red
‘If you give him a new, better research tool, he suddenly sees an artery in the buttock that doesn’t actually belong there. That is exactly how we think about the new findings.’
However, the researchers do present a few theories behind the anomalies, which require more information about waves – and not just their speed – to draw robust conclusions.
It could be ancient, silica-rich material that has been there since the mantle formed about four billion years ago.
Alternatively, they may be zones where iron-rich rocks accumulate due to mantle movements over billions of years.
“There are a wide range of possible explanations for the detection of positive wave speed anomalies in the Earth’s (lower) mantle, apart from the presence of submerged plates,” they conclude in their paper.
‘Our research underlines the crucial role of full waveform inversion as an indispensable tool in mantle research.’