More than 2,000 years ago, Plato wrote about a land called Atlantis, where a mighty empire vanished beneath the waves after a series of "excessively violent earthquakes and floods." His tale has inspired plenty of nonsense in the centuries since, but now it seems that Plato was on to something. New research shows that lost continents are a real thing, and they have had a big impact on human life — though not in the way Plato imagined.
Douwe van Hinsbergen, a geologist at Utrecht University in the Netherlands, has been exploring one of the most dramatic of these lost continents — known as Greater Adria. In a paper published in early September in the journal Gondwana Research, he and his colleagues studied rocks around and beneath the Mediterranean Sea to reveal the full extent of Greater Adria for the first time. "It's enormous! About the size and rough shape as Greenland," he says.
If you don't recall seeing Greater Adria on a map, there's a reason for that. It is completely buried — not under the ocean, but beneath southern Europe. About 140 million years ago, the two continents began to collide. Greater Adria got bulldozed and buried in the process and mostly sank beneath what is now Italy, Greece and the Baltics.
And Greater Adria is not unique. Emerging studies of Earth's mantle show likely traces of past lost continents. Analysis of ancient rocks suggest that almost all of Earth's earliest continents might have disappeared, taking with them much of the history of life on this planet. The evidence of how life first appeared may be lost somewhere down there in the depths.
But lost continents are not entirely lost. Like lost civilizations, they leave traces behind, if you know how to look for them. Van Hinsbergen notes that rocks from Greater Adria got scraped off and incorporated onto the Alps, while whole chunks got embedded in southern Italy and Croatia. Even the parts of Greater Adria that got shoved dozens of miles down into the mantle, the layer below the crust, continue to influence modern Europe.
Under tremendous heat and pressure and over tens of millions of years, limestone rocks from Greater Adria turned into marble. Friction between Greater Adria and Europe then pulled the sunken rocks back to the surface, where people found them and mined them. "That's where the marble came from that the Romans and the Greeks used for their temples," van Hinsbergen says.
Plato was literally standing on the remains of a real Atlantis. He just had no idea.
Earth's hidden eighth continent
Greater Adria long remained unknown because it has been almost completely obliterated and obscured. But at least one other lost continent has been hiding in plain sight.
Maps of the ocean floor show a vast elevated region surrounding the islands of New Zealand, a formation known as Zealandia. Two years ago, a team led by geologists Nick Mortimer of GNS Science, a geological research company, and Rupert Sutherland of Victoria University Wellington, both in New Zealand, combined those maps with measurements of surface gravity and analysis of seafloor samples to show that Zealandia is much more than a bump in the ocean: It's a single, continuous continent, the eighth in the world (or the seventh, if you lump together Europe and Asia as Eurasia), about two-thirds the size of Australia and more than twice as large as Greater Adria.
Like Greater Adria, Zealandia has been overlooked because it's a low-rider. A few hundred million years ago, during the time of the dinosaurs, it was a proud part of the grand supercontinent known as Gondwana. "Then it got separated 85 million to 100 million years ago," Sutherland says. "It got stretched and thinned, resulting in a lower elevation, and it was also affected by the development of the "Pacific Ring of Fire," a zone of volcanic activity that rims the Pacific Ocean.
These insults conspired to sink Zealandia beneath the waves. Today it is 94 percent underwater, with the islands of New Zealand and New Caledonia as its only major outposts of dry land. During its long existence, though, additional parts of Zealandia probably popped above sea level. The resulting islands would have provided crucial stepping stones for life to migrate across the southwestern Pacific and may help explain the unusual plants and animals there.
Sutherland recently led an ocean-drilling project to retrieve Zealandia's lost history, the geological equivalent of sending a sub down to explore the Titanic. He plans to reveal the results soon, "hopefully by the end of the year."
Lands that come and go
It now seems that Zealandia and Greater Adria are just two recent examples of what was once a regular Atlantis-like process. Continents were not always stable fixtures of our planet, according to University of Adelaide geophysicist Derrick Hasterok. Early in our planet's history, more than 2 billion years ago, they were fragile and transient things, easily crumbling, fracturing, or simply eroding away.
The surprising reason for all this instability? Radioactivity. The Earth was born with a lot more radioactive elements than it has now (much of them have since decayed away), Hasterok says, and those elements preferentially collect in continental rocks. When the first continents formed, they sowed the seeds for their own demise. The only way he knows they ever existed is by the curious lack of high-radioactivity rocks in the modern continents. Those rocks don't exist, because the continents in which they lived are long gone.
"I imagine high heat-producing crust being produced and then radioactivity heating it internally until it melted, or the crust became soft and collapsed," Hasterok said in an email.
Nobody will ever know what kinds of events took place on those early continents. But the more recent past is still in evidence, and van Hinsbergen is finding ways to read it. He has created an "Atlas of the Underworld" to document what has become of the parts of Earth's crust that got pulled into the mantle. He's now trying to match the Atlas with studies of geology on the surface, such as the new map of Greater Adria, to produce more accurate reconstructions of how continents moved and collided in the past.
All this is more than an intellectual exercise. Just as Greater Adria pulled marble up to the surface in Europe, other continental collisions have excavated precious ores and minerals. "We hope it will lead to the exploration of new deposits," van Hinsbergen says. "The world needs more copper and rare-earth elements for the green revolution. This could help us find them."
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