This week, a group of geologists report that they’ve found a lost continent off the coast of Scotland. 55 million years ago, about 10 million years after dinosaurs died out, a chunk of the seafloor erupted from beneath the water.
It created a small continent that existed for at least a million years, covered in dramatic mountains and valleys, and irrigated with streaming rivers. Eventually the landscape sank back beneath the waves, its once-sunny mountains buried beneath 2km of seabed.
How did this happen? The answer reveals that our planet is even more dangerous and magnificent than we knew.
In Nature Geoscience, Earth scientist Ross A. Hartley and colleagues describe their discovery, and offer some theories about how an entire continent could rise and fall in a million years – a brief moment in geological time. Above, you can see the image they created of part of the continent, including its coastline and a mountain whose slopes were deeply cut by rivers. Write Hartley and his team:
This image was constructed from sound waves which are bounced off different rock layers at depth. An ancient meandering riverbed can easily be seen.
They found this lost continent after using sound waves to map a volume of 10,000 square kilometers on the northwest continental shelf of Europe. Based on the weathering of rocks the researchers studied beneath the waves, it’s clear that a huge chunk of the seafloor was once above water, being eroded by wind and sun.
So how did it happen? Hartley and colleagues suggest that this continent rose out of the water on what some geologists call a “thermal anomaly”, and others call a “mantle plume“. You could also call it a giant explosion inside the Earth. Basically, as you can see in the image at left, superheated rock in the Earth’s mantle (near the core of the planet) can sometimes create giant plumes of heat that push to the surface of the planet. When this happens, radical disruptions can occur – such as huge chunks of the seafloor rising suddenly above the surface of the ocean. And that’s what probably created this short-lived landmass.
This is the sort of thing that could only happen on Earth. Our planet has the unique feature of being both hard and soft at the same time: On the surface of Earth, we have several vast chunks of hard crust, the continental plates, floating atop a rapidly churning layer of superheated liquid rock. And sometimes, the superheated liquid rock spurts up out of cracks between the hard crusts, creating your thermal anomalies, volcanoes, and other disaster movie scenarios.
But this mystery continent was part of a disaster even bigger than a giant volcano. It appeared during the Paleocene-Eocene Thermal Maximum, or the most recent period of global warming in Earth’s history. It was a time possibly much like ours, when the atmosphere was full of carbon and the temperature was going up. Scientists have long wondered what caused this ancient period of global warming, and this thermal anomaly may help answer that question.
Here you can see a map of the Icelandic Plume, which is probably what set this weird geological story in motion. Commenting on the discovery of the lost continent, Earth scientist Phillip A. Allen explains how it could be connected to global warming:
Intriguingly, the timing of formation of the ancient landscape west of the Orkney–Shetland Islands coincides with a global climatic event known as the Palaeocene–Eocene Thermal Maximum – a period of rapid and extreme global warming. Triggers of this climatic event are unclear, but could be linked to the release of large quantities of methane stored in sediments on the sea bed. Uplift of the sea bed would have caused the methane stored in the ocean floor to become unstable, triggering its release into the atmosphere. Pulses of hot mantle rising up in the Iceland mantle plume therefore provide a viable mechanism to elevate the sea floor at this time. Furthermore, about 33–34 million years ago, the climate suddenly cooled causing the planet to undergo a transition from a greenhouse to an icehouse world. This climatic change has been linked to periods when activity in the Iceland plume was suppressed, causing the sea bed between Iceland and Greenland to subside.
In other words, this thermal anomaly sent a plume of superheated rock to the Earth’s surface, warming the waters and thawing the methane beneath them. Our lost continent rose to the surface as greenhouse gases filled the atmosphere, making the birth of this landmass into a veritable environmental apocalypse.
Scientists are trying to understand when such an event might happen again, and what we can learn from it that might help us deal with climate change today. Meanwhile, I wait for the disaster movie version of this scenario from Earth’s past, which will hopefully include references to Atlantis and ancient alien civilisations.
Read the full scientific paper via Nature Geoscience.