Tag: continent

Massive asteroid may have kickstarted the movement of continents

Akshat RathiLeave a comment

Earth was still a violent place shortly after life began, with regular impactors arriving from space. For the first time, scientists have modelled the effects of one such violent event – the strike of a giant asteroid. The effects were so catastrophic that, along with the large earthquakes and tsunamis it created, this asteroid may have also set continents into motion.

The asteroid to blame for this event would have been at least 37km in diameter, which is roughly four times the size of the asteroid that is alleged to have caused the death of dinosaurs. It would have hit the surface of the Earth at the speed of about 72,000kmph and created a 500km-wide crater.

At the time of the event, about 3.26 billion years ago, such an impact would have caused 10.8 magnitude earthquakes – roughly 100 times the size of the 2011 Japanese earthquake, which is among the biggest in recent history. The impact would have thrown vapourised rock into the atmosphere, which would have encircled the globe before condensing and falling back to the surface. During the debris re-entry, the temperature of the atmosphere would have increased and the heat wave would have caused the upper oceans to boil.

AGU

Donald Lowe and Norman Sleep at Stanford University, who published their research in the journal Geochemistry, Geophysics, Geosystems, were able to say all this based on tiny, spherical rocks found in the Barberton greenstone belt in South Africa. These rocks are the only remnants of the cataclysmic event.

According to Simon Redfern at the University of Cambridge, there are two reasons why Lowe and Sleep were able to find these rocks. First, the Barberton greenstone belt is located on a craton, which is the oldest and most stable part of the crust. Second, at the time of the event, this area was at the bottom of the ocean with ongoing volcanic activity. The tiny rocks, after having been thrown into the atmosphere, cooling, and falling to the bottom of the ocean, then ended up trapped in the fractures created by volcanic activity.

This impact may have been among the last few major impacts from the Late Heavy Bombardment period between 3 and 4 billion years ago. The evidence of most of these impacts has been lost because of erosion and the movement of the Earth’s crust, which recycles the surface over geological time.

However, despite providing such rich details about the impact, Lowe and Sleep are not able to pinpoint the location of the impact. It would be within thousands of kilometres of the Barberton greenstone system, but that is about all they can say. The exact location may not be that important, Lowe argued: “With this study, we are trying to understand the forces that shaped our planet early in its evolution and the environments in which life evolved.”

One of the most intriguing suggestions the authors make is that this three-billion-year-old impact may have initiated the the movement of tectonic plates, which created the continents that we observe on the planet.

The continents ride on plates that make up Earth’s thin crust; the crust sits on top of the mantle, which is above a core of liquid iron and nickel. The heat trapped in the mantle creates convection, which pushes against the overlying plates.

All the rocky planets in our solar system – Mercury, Venus, Earth and Mars – have the same internal structure. But only Earth’s crust shows signs of plate motion.

A possible reason why Earth has moving plates may be to do with the heat trapped in the mantle. Other planets may not have as much heat trapped when they formed, which means the convection may not be strong enough to move the plates.

However, according to Redfern: “Even with a hot mantle you would need something to destabilise the crust.” And it is possible that an asteroid impact of this magnitude could have achieved that.The Conversation

First published on The Conversation.

Submerged continent found

Akshat RathiLeave a comment

A group of scientists from Norway, Germany, South Africa and the U. K. have discovered a submerged continent in the Indian Ocean.

Their measurements predict that the continent, which they have named Mauritia, lies under Mauritius and its broken chunks today extend more than 1000 km northwards till Seychelles.

The discovery was sparked when they found crystals called zircons on Mauritian beaches. Zircons are resistant to erosion or chemical change and some of the ones they found were almost two billion years old, much older than any of the regular soil or sand samples found on nearby islands. Such old crystals, they thought, could only belong to a submerged continent, and may have perhaps been pushed up on the surface by underwater volcanoes.

To confirm whether these zircons indeed belonged to such a continent, they consulted satellite data which can help detect submerged land masses.

Nick Kusznir, professor of geophysics at the University of Liverpool in the U. K. and co-author of the paper that appeared this week in the journal Nature Geoscience, says: “We found that under Mauritius there were areas with an unusually thick Earth’s crust.”

In deep oceans the thickness of Earth’s crust, which forms the upper layer of the planet and protects us from the extremely hot magma underneath it, is about seven km.

But underneath Mauritius and leading to Seychelles, which is more than 1,000 km away, there were large chunks of the crust that were as thick as 30 km. “While we cannot be certain about the origins of the zircons, when combined with the evidence of thicker crusts in such big parts of the ocean floor, we can be quite certain that a small continent existed underneath Mauritius,” says Kusznir. There are a number of popular myths about submerged continents.

For instance, in the 19th century Lemuria, a large submerged continent in the Indian Ocean, was considered to extend from Antarctica to Kanyakumari. But its claimed existence did not stand the test of science. The Earth’s crust consists of seven or eight major “plates”, which are slowly but constantly moving relative to each other.

Over millions of years these have shaped how the world looks today. Some 140 million years ago, the Indian subcontinent split from a supercontinent called Gondwana, which also consisted of modern Africa, Australia, Antarctica and South America.

It eventually collided with the Eurasian plate some 50 million years ago, raising the Himalayas in the process.

Scientists predict that it was in between leaving Gondwana and colliding with the Eurasian plate that this continent Mauritia may have existed as an archipelago, a cluster of islands, squeezed in between Madagascar and the Indian subcontinent.

On the uses of finding such a submerged continent Kusznir says: “A better understanding of the sea floor and such submerged land masses can help us in better exploration of oil and gas in the oceans.”

First published in The Hindu.

Reference: Torsvik et al. Nature Geoscience 2013 http://dx.doi.org/10.1038/ngeo1736
Image from here.

TLDR: Submerged continent found in the Indian ocean

Akshat Rathi2 Comments
The island M stands for Mauritius

Scientists have discovered a submerged continent in the Indian ocean, between Madagascar and India. According to sediments found on the coast of Mauritius, at some point during the last 2 billion and 600 million years ago, there was an archipelago that separated from Madagascar and the Indian sub-continent. They then got submerged during the tectonic plate movements that resulted in the way land masses exist today.

Reference:  Torsvik, T. H. et al. Nature Geosci. 2013, 223. http://dx.doi.org/10.1038/NGEO1736

Further reading: Sid Perkins in Nature News

Image credit: Nature Geoscience (Supplementary information)

Update: A reader pointed out that perhaps this was the origin of the legends of Lemuria. Although that is not accurate, the Wikipedia article on Lemuria is worth a read.