Lost continent revealed in new reconstruction of geological history

Take a hike along the mountain belts scattered around the Adriatic Sea, and you may find yourself clambering across the crumpled leftovers of a long-lost continent.

This rocky jumble represents the ruins of a Greenland-size piece of continental crust that was demolished millions of years ago, scientists report this month in the journal Gondwana Research. The saga of the continent’s demise is part of a new report that re-creates the last 240 million years of the Mediterranean’s tectonic history in unprecedented detail.

The model shows how this continent first separated from what is now Spain, southern France, and northern Africa, forming a separate landmass the team has formally dubbed Greater Adria. But as the planet’s rocky plates continued to inexorably jostle about, this continent tumbled down into several subduction zones – Earth’s destructive geological maws.

As it dove into the hellish depths of the mantle, the top layer of the continent was scraped away, as if a titan were peeling a colossal potato. This wreckage was dumped onto the overlying plates, ready to form future mountains along the spine of Italy, as well as in Turkey, Greece, the Alps, and the Balkans.

Several slivers of the continent dodged both a gnarly shave and slow obliteration through subduction. These unsullied relics of Greater Adria can be found today in the heel of Italy’s boot, scattered from Venice to Turin, and in Croatia’s Istria region—which means you can take a holiday on the splinters of a lost continent.

Reconstructing this slice of our geological past is key to understanding the present, says study leader Douwe van Hinsbergen, an expert in tectonics and ancient geography at Utrecht University.

“Everything that you see around you that wasn’t wood or cloth was found by a geologist in a mountain,” he says. Ores, metals, and minerals that are now vital to civilisation can be found within these peaks, and over time, interlinked caches of them have been fragmented by plate tectonics pandemonium.

Models like the one in the new study can allow us to rewind the clock and watch this dissection take place. If a deposit of copper, for example, is found in one country, such reconstructions allow us to work out where its once-connected shards may have ended up, effectively creating the treasure maps of the modern era.

Rewinding the jigsaw

Re-creating the Mediterranean’s geological evolution since the Triassic period presented some serious challenges. Scientists have had a broad understanding of the region’s tectonic history for some time now, but the labyrinthine jigsaw made a more detailed analysis daunting.

“The Mediterranean is a dog’s breakfast,” says Robert Stern, a plate tectonics expert at the University of Texas at Dallas who was not involved with the work.

Within this messy region, several geologists had previously found hints of the existence of a lost continent, but key details in its story were proving to be elusive. Its remains are strewn across 30 or so countries, each with their own models, maps, survey techniques, and terminologies. The continent even had a range of possible names in the literature.

To sort things out, the team spent 10 years collecting a deluge of geological and geophysical data from all over the region and plugging it into their model, using a software called GPlates. In the last 15 years or so, this software, which van Hinsbergen describes as “relatively idiot-proof,” has allowed for more detailed visualisation and tweaking of plate tectonics systems. The team’s painstaking process revealed the missing chapters in this lost continent’s tangled tour.

Around 240 million years ago, Greater Adria was part of the Pangea supercontinent, squashed up against what is now northern Africa, Spain, and southern France. It broke away from Africa 20 million years later, then separated from France and Spain 40 million years after that to become an isolated continent.

Although its geography remains unclear for now, it was probably a bit like the largely submerged continent of Zealandia, with chunks of land (in this case, New Zealand and New Caledonia) sticking up from the sea. It might also have been a bit like the Florida Keys, with an archipelago of non-volcanic islands propped up above the waves.

Monumental effort

The destruction of Greater Adria began in earnest 100 million years ago, when it encountered what is now southern Europe and parts of it dove beneath a range of plates all over the region. This scattershot subduction of the continent meant that “every little piece had its own history,” van Hinsbergen says. “And then you end up with the mess that is now the Mediterranean.”

Crucially, though, “if continents disappear, they tend to leave marks,” van Hinsbergen says, and that includes the scars of mountain building.

You can make mountains when two continents collide, as what happened to form the Himalaya mountain range. But you don’t always need a collision zone to make mountains. Subducting plates may also have their top layers scraped off by the upper plate, says Stern, and these scrapings can accumulate and crunch up to form mountains. 

This principle was vital for reconstructing the Mediterranean’s past, van Hinsbergen says. Geologists can match the amount of mountain-building leftovers seen today to the length of the section of the original plate that has been swallowed into the underlying mantle, which allows them to more precisely model the pieces of the ancient jigsaw puzzle.

This work has “clearly been a monumental undertaking,” says geophysicist Dietmar Müller, co-leader of the EarthByte Project at the University of Sydney, the research group that developed GPlates. The effort that went into it is comparable to that involved in his own group’s re-creation of the entire planet’s tectonic story—but what this new work loses in sheer scale, he says, it makes up with breathtaking detail.