Name: 宇宙の旅-南極の運命 (Cosmic Journeys - Fate of Antarctica)
Uploaded: 2021-01-14T05:15:09.000Z
Duration: 25 min 24 s
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In a world buffeted by rising temperatures, rising sea levels, and changing climate patterns,

If you could go back to a time 250 million years ago.

What�s now the frozen continent of Antarctica, was a land of forests and flowing water.

In a warmer, wetter world, it harbored a wide diversity of plants and animals.

In this period, known as the Permian, Antarctica was at the southern end of a vast single continent

Within the sweeping evolution of this grand continent, a single event would reverberate

An asteroid headed toward the southern hemisphere.

At up to fifty kilometers in diameter, it would have been four to five times larger

than the one thought to have killed off the dinosaurs.

It crashed into a region that�s now part of East Antarctica, but its impact was global

One theory is that it sent powerful seismic waves to the exact opposite, or antipodal,

On what�s now Siberian Russia, a plume of magma pushed up through Earth�s crust. For

tens of thousands of years, lava flooded the landscape.

A release of toxic elements, a rush of carbon dioxide into the atmosphere, acid rain, all

led to one of the worst mass extinctions in history.

70% of all species on the planet vanished.

On Earth, traces of most major impacts are obscured by erosion or geological activity.

A new type of observational tool is now allowing scientists to see them.

In 2002, they launched the twin spacecraft of the GRACE mission, short for Gravity Recovery

Its goal was to map subsurface features by measuring variations in Earth�s gravity.

A gravitational surge or a dip causes the distance between the two craft to change,

which GRACE measures down to the width of a human hair.

Down along the Eastern part of Antarctica, GRACE detected an immense subsurface presence.

Scientists matched it up with subtle rings etched on the wider landscape, and with chemical

traces found in nearby mountains. They concluded that a large meteor had struck at the end

It would have a lasting impact on Antarctica�s long and tumultuous journey.

That journey began in the break up of an immense continent known as Rodinia, beginning around

In those days, Antarctica basked in the tropical sun.

Some 300 million years later, as Earth�s landmasses reshuffled into the supercontinent

When Pangaea finally fragmented, Antarctica began a steady drive toward the southern pole

as part of the great southern continent of Gondwana.

At around 130 million years ago, a series of rifts developed in Earth�s crust, tearing

South America and Africa away from Gondwana.

Australia finally split off at about 85 million years ago, leaving Antarctica on its own.

Because the rift between the two cuts through the Permian crater, one theory holds that

the force of the impact may have actually initiated it.

Now separated from its sister landmasses, Antarctica carried a rich biological legacy,

evident in fossils recently pulled from the frozen ground.

The Cryolophosaurus, from 190 million years ago, was in a class of meat eaters called

These bipedal creatures gave rise to some of the fiercest predators ever, including

Out on the West Antarctic Peninsula, scientists turned up a smaller theropod from 70 million

years ago. This swift predator would have grown to about two meters in length.

From the same period, another group found a young plesiosaur, a marine reptile that

If it had reached adulthood, it would have grown to around 10 meters in length.

From a continent that once hosted dinosaurs, Antarctica grew steadily more hostile to life.

Wind the clock forward, to 50 million years ago.

All around the world, warm conditions were giving way to cooler, drier times.

The new era saw a decline in the heat-trapping atmospheric gas, carbon dioxide.

Around Antarctica, conifers and other cold-tolerant plants took hold.

In some areas, they gradually turned to tundra.

Ice remained year round, gradually forming a thick sheet.

At the same time, powerful wind currents circling the pole from west to east drove the circumpolar

Known as the mightiest current in the world, it helped shield the continent from tropical

A combination of factors came together: declining CO2, the isolation of Antarctica, and the

tendency of permanent ice stores to reflect more solar energy back to space.

At around two and a half million years ago, Earth entered the last great ice age, the

Year after year, as storms rolled off the oceans, they deposited layer upon layer of

Today, fully 70 percent of all the fresh water on the planet is here, in ice that averages

Antarctica today is known as the windiest, driest, and coldest place on Earth.

There are no permanent human populations, only a few thousand scientists and support

workers living at scattered research stations.

At the Russian Vostok station, in July 1983, scientists documented the lowest natural temperature

A recent calculation based on satellite data went even lower, to -93.2 degrees Celsius.

But as cold and isolated as it is, Antarctica is not immune to changes in the larger environment.

Take, for example, this reconstruction of the continent during the last glacial maximum,

Compare it to this image of the current interglacial period. It shows how much ice the continent

In recent years, the rate of ice loss has picked up speed.

Scientists have turned to satellites to find out where and how quickly this trend is playing

In these images, from the GRACE mission, areas that lost ice are shown in blue, while orange

European scientists backed up this finding with radar data from the Cryosat-2 spacecraft.

By tracking changes in the elevation of Antarctic ice, they found that the continent lost on

average 159 billion tons of ice each year from 2010 to 2013.

That�s an increase of 31% per year over the previous five years.

Like GRACE, Cryosat-2 found that the greatest losses have occurred in West Antarctica, especially

where a series of fast-flowing glaciers empty into the Amundsen Sea.