In a remote area of northwest Greenland, [music rises]
an international team of scientists has
made a stunning discovery, buried beneath a kilometer
of ice. It’s an impact crater …
300 meters deep … 31 km wide
… much bigger than Washington, D.C.,
even bigger than Paris, and it’s probably
one of the youngest large impact craters on Earth.
The relentless spread of the Greenland Ice Sheet has covered the crater, obscuring
obscuring it from view for thousands if not hundreds of thousands of years.
Even so, scientists say it was essentially hiding in plain sight.
So what finally revealed its presence?
It all started with a rock … a map …
and a connection made by scientists at the Natural History Museum in Copenhagen.
Each day, scientists there pass by a large
iron meteorite found in Greenland decades ago.
One day, they got a new map of the bedrock topography beneath the ice sheet,
mostly based on ice-penetrating radar data collected
onboard NASA’s P-3 aircraft over two decades. [Sound of aircraft engine]
This map gets more refined all the time, yet there are still areas open
to interpretation, including the conspicuously semicircular
edge of the ice sheet, drained by the Hiawatha Glacier.
There, the data showed a circular depression in the bedrock,
near the region where that courtyard meteorite had been found.
In May of 2016, the team sent the German research plane
Polar 6 to fly over Hiawatha Glacier with a powerful new
ice-penetrating radar.
Radar waves can travel through the ice, measuring its thickness
and internal structure. Studying data from this airborne survey,
the scientists confirmed the telltale bowl shape and central peaks
beneath Hiawatha Glacier. They also found that the oldest ice
in this crater was actually fairly young, by Greenland standards,
and had experienced a great disturbance in its flow toward the end
of the last ice age. [Sound of hammer on rock]
The team then visited the area on foot, and in sediments deposited by a river
draining out of the glacier, they found grains of the mineral quartz that showed signs
of being physically shocked in a massive impact.
Models suggest, the asteroid was more than a kilometer wide.
The Hiawatha crater is one of the 25 largest known
impact craters on Earth, and the first found under any of
our planet’s ice sheets.Crucially, the Hiawatha impact
crater still looks like an impact crater, even though it’s covered by ice
and seems to be rapidly eroding. The data as a whole
suggests it’s quite young – geologically speaking
But we don’t know exactly when an asteroid sped
toward Earth, through the atmosphere, and into the
planet’s crust in Northwest Greenland. [Sound of impact]
It was likely less than 3 million years ago.
But it might have been as recently as during the last ice age,
12 to 115 thousand years ago.
The impact could have also occurred when ice already covered Greenland
and it would have instantly vaporized billions of tons of ice and re-routed
the flow of ice and water into the ocean.
Whenever the impact happened, life on Earth at the time would have been profoundly affected.
An impact of this size is unlikely
to happen again soon, but evidence that it might have happened
not so long ago, in Earth’s history is essential to assessing the risk today.
This is the first study of the Hiawatha
impact crater, but it still holds many secrets waiting to be discovered.
[music fades]