What are lost continents, and why are we discovering so many?



Lord Howe Island is one of the few places where the lost continent of Zealandia is exposed above sea level.
SHUTTERSTOCK

Maria Seton, University of Sydney; Joanne Whittaker, University of Tasmania, and Simon Williams, University of Sydney

For most people, continents are Earth’s seven main large landmasses.

But geoscientists have a different take on this. They look at the type of rock a feature is made of, rather than how much of its surface is above sea level.

In the past few years, we’ve seen an increase in the discovery of lost continents. Most of these have been plateaus or mountains made of continental crust hidden from our view, below sea level.

One example is Zealandia, the world’s eighth continent that extends underwater from New Zealand.

Several smaller lost continents, called microcontinents, have also recently been discovered submerged in the eastern and western Indian Ocean.

But why, with so much geographical knowledge at our fingertips, are we still discovering lost continents in the 21st century?

We may have found another

In August, we undertook a 28-day voyage on the research vessel RV Investigator to explore a possible lost continent in a remote part of the Coral Sea. The area is home to a large underwater plateau off Queensland, called the Louisiade Plateau, which represents a major gap in our knowledge of Australia’s geology.




Read more:
Explainer: the RV Investigator’s role in marine science


On one hand, it could be a lost continent that broke away from Queensland about 60 million years ago. Or it could have formed as a result of a massive volcanic eruption taking place around the same time. We’re not sure, because nobody had recovered rocks from there before – until now.

An extremely violent eruption formed this volcanic rock we recovered.
Author supplied

We spent about two weeks collecting rocks from this feature, and recovered a wide variety of rock types from parts of the seafloor as deep as 4,500m.

Most were formed through volcanic eruptions, but some show hints that continental rocks are hiding beneath. Lab work over the next couple of years will give us more certain answers.

Down to the details

There are many mountains and plateaus below sea level scattered across the oceans, and these have been mapped from space. They are the lighter blue areas you can see on Google Maps.


However, not all submerged features qualify as lost continents. Most are made of materials quite distinct from what we traditionally think of as continental rock, and are instead formed by massive outpourings of magma.

A good example is Iceland which, despite being roughly the size of New Zealand’s North Island, is not considered continental in geological terms. It’s made up mainly of volcanic rocks deposited over the past 18 million years, meaning it’s relatively young in geological terms.

The only foolproof way to tell the difference between massive submarine volcanoes and lost continents is to collect rock samples from the deep ocean.

Plenty of soft, gloopy sediment covers the bottom of the Coral Sea.
Author provided

Finding the right samples is challenging, to say the least. Much of the seafloor is covered in soft, gloopy sediment that obscures the solid rock beneath.

We use a sophisticated mapping system to search for steep slopes on the seafloor, that are more likely to be free of sediment. We then send a metal rock-collecting bucket to grab samples.

The more we explore and sample the depths of the oceans, the more likely we’ll be to discover more lost continents.

The ultimate lost continent

Perhaps the best known example of a lost continent is Zealandia. While the geology of New Zealand and New Caledonia have been known for some time, it’s only recently their common heritage as part of a much larger continent (which is 95% underwater) has been accepted.




Read more:
Explorers probe hidden continent of Zealandia


This acceptance has been the culmination of years of painstaking research, and exploration of the geology of deep oceans through sample collection and geophysical surveys.

Continental rocks recovered from a microcontinent in the Indian Ocean are similar to rocks found in Western Australia.
Author supplied

New discoveries continue to be made.

During a 2011 expedition, we discovered two lost continental fragments more than 1,000km west of Perth.

The granite lying in the middle of the deep ocean there looked similar to what you would find around Cape Leeuwin, in Western Australia.

Other lost continents

However, not all lost continents are found hidden beneath the oceans.

Some existed only in the geological past, millions to billions of years ago, and later collided with other continents as a result of plate tectonic motions.

Their only modern-day remnants are small slivers of rock, usually squished up in mountain chains such as the Himalayas. One example is Greater Adria, an ancient continent now embedded in the mountain ranges across Europe.

Due to the perpetual motion of tectonic plates, it’s the fate of all continents to ultimately reconnect with another, and form a supercontinent.

But the fascinating life and death cycle of continents is the topic of another story.




Read more:
How Earth’s continents became twisted and contorted over millions of years


The Conversation


Maria Seton, ARC Future Fellow, University of Sydney; Joanne Whittaker, Associate Professor, University of Tasmania, and Simon Williams, Research Fellow, University of Sydney

This article is republished from The Conversation under a Creative Commons license. Read the original article.

Explorers probe hidden continent of Zealandia



File 20170902 27261 1a08rs6
The Joides Resolution.
Tim Fulton, CC BY-ND

Rupert Sutherland, Victoria University of Wellington

Zealandia made global headlines earlier this year when scientists announced that it counts as a new continent.

Now it is coming under closer scientific scrutiny. We are currently halfway through an expedition to drill into this vast underwater plateau of continental crust, and we can already reveal that Zealandia’s geography changed more dramatically and more recently than anyone had thought.

As the first core samples from Zealandia emerge, chief scientists Rupert Sutherland and Jerry Dickens explain what that means for the continent’s evolution.

Earth’s hidden continent

There are seven continents on Earth: Eurasia, North America, South America, Africa, Antarctica, Australia and now Zealandia.

Zealandia is about two-thirds the size of Australia, but 94% of it lies deep below the southwest Pacific Ocean. Its only major landmasses are New Zealand to the south and New Caledonia to the north.

Very little is known about it, because most of it lies more than a kilometre deep beneath the Pacific Ocean.

The Zealandia continent also encompasses some smaller bits of land, including Norfolk Island, the Lord Howe group and some sub-antarctic islands. These islands were discovered hundreds of years ago, but the submerged part was only recognised as a continent in recent decades. It remains sparsely surveyed and sampled. We have better maps of the moon.

We are a team of 32 scientists from 12 different countries and our expedition is part of the International Ocean Discovery Program, which coordinates seagoing explorations of Earth’s history recorded in sediments and rocks beneath the ocean floor.

Our ship, the Joides Resolution is a floating village and laboratory, equipped with a drill rig that can take core samples from the seafloor. The samples we have collected so far show clear signs of major geographic changes and volcanic eruptions that were related to formation of the Pacific Ring of Fire, a chain of undersea volcanoes, ocean trenches, seamounts and hydrothermal vents that formed some 40 to 50 million years ago.

IODP research vessel Joides Resolution leaving Townsville in July at the start of its voyage to Zealandia.
Mark Leckie, University of Massachusetts Amherst, CC BY-ND

Zealandia exposed

There is a buzz of excitement on the ship. After more than a month at sea we are mid-way through our expedition and have drilled into the seabed at four sites. You can’t beat the old-fashioned thrill of exploration and discovery.

Co-chief scientists Jerry Dickens (left), Rice University, USA, and Rupert Sutherland (right), Victoria University of Wellington, New Zealand, drain excess sea water from a newly-collected sediment core.
Tim Fulton, IODP/TAMU, CC BY-ND

We are re-writing the geological history of Zealandia on our voyage. Zealandia was first recognised about 50 years ago and ideas for how it formed were published then, but the only previous expedition that has drilled deep enough into the seabed to collect useful evidence was undertaken in 1971.

It appeared back then that Zealandia separated from Australia and Antarctica about 80 million years ago, when dinosaurs roamed the Earth. It then subsided deep beneath the waves and was lost.

However, fossils and volcanic rocks show that northern Zealandia, an area about the size of India, was radically affected by formation of the Pacific Ring of Fire.

To collect sediment cores from deep beneath the seabed we need a drill that may be more than 5000 metres long and weigh more than 200 tonnes.
Tim Fulton, IODP/TAMU, CC BY-ND

Our preliminary observations suggest that regions now under more than 1000 metres of water became land or shallow seas, and other regions that are now under 3000 metres of water may have been much shallower, or even land. Changes in geography were massive, and may help explain how the unique plants and animals of the southwest Pacific were able to disperse and evolve.

Undersea exploration

Explorers are normal people doing extraordinary things. Exploration isn’t easy. Not everything goes to plan. The hours are long, you share a small room with someone you didn’t know before the voyage, and you miss your family and friends.

Texas A&M University technical staff process a recently-collected sediment core.
Rupert Sutherland, CC BY-ND

Sea sickness is not your friend if you spend 14 hours a day looking down a microscope at fossils that are so small you could fit hundreds on the head of a pin. So why do we do it?

It is hard to describe the excitement of discovery. Every time we get a new core on deck it is like unwrapping a present. What will it be? A curiosity to keep you busy for another few days, or key evidence to reconstruct the history of a hidden continent?

Our goals are to understand why Earth’s surface moves (the study of plate tectonics) and how greenhouse climate systems work (climate change). The southwest Pacific location makes Zealandia ideal for testing ideas on how the earth works.

The formation of the Pacific Ring of Fire changed the way our planet moved: new volcanoes and mountains grew, natural resources formed, and the changes had long-term effects on global climate.

Zealandia was closer to the South Pole 50 million years ago, but had a warm climate. How was this possible? If computer models can’t predict such warm conditions in the past, could models of future global warming also be underestimates?

The ConversationThe answers to these and many more questions lie beneath the waves, recorded in sediment layers that have accumulated over millions of years.

Rupert Sutherland, Professor of tectonics and geophysics, Victoria University of Wellington

This article was originally published on The Conversation. Read the original article.