Date: September 5, 2010
Title: The Nordlinger Ries: A Deep Impact in the Heart of Europe
Podcaster: Colm Ryan
Organization: Blackrock Castle Observatory in Cork, Ireland – www.bco.ie
Colm’s blog: http://woodpigeon01.wordpress.com/
Description: Colm Ryan travels to southern Germany to explore some of the world’s best preserved large impact craters.
Bio: Colm Ryan has been fascinated by the skies for over 30 years and is keenly interested in all things science related. He is an engineering graduate of Univerity College, Cork, Ireland. Colm lives in Ireland and has four children.
Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by John Sandlin because a little astronomy illuminates the darkest nights.
Transcript:
It’s a few minutes past midday, July 27th, and a thunderstorm has just rolled through this small town in southern Germany. I’ve come here to visit a museum with a difference. It’s a museum dedicated to one of the greatest catastrophes this part of the world has ever witnessed. The event extinguished all life for thousands of square miles. This is the town of Nordlingen and I have come to see for myself the scene of an enormous asteroid impact event.
To understand what happened, we need to go back in time to the Europe of 15 million years ago. It was the Miocene Epoch, a warm period characterized by the spread of grassland and the appearance of many modern mammals. In this part of Europe, the climate was at least ten degrees warmer than it is today. The countryside was a mix of dry plains and warm, almost tropical, valleys. Unlikely creatures roamed the landscape. Crocodiles, elephants, rhinoceroses and giant tortoises to name a few. Flamingoes flew in the skies.
Two asteroids were to change all that. Traveling side by side, their course through space was about to be rudely interrupted by a large inner planet, getting in their way. The small one was about 300 feet in diameter. Its companion was ten times longer – about half a mile in width. They were both speeding towards the Earth at 45,000 miles per hour.
The impacts were sudden. The smaller asteroid hit the region around Steinheim in Germany; the large one, 25 miles away in Nordlingen. Earth’s atmosphere, normally good at shielding the Earth from small meteoroids, would have provided no protection at all. The asteroids punched themselves into our planet, with the largest one coming to a rest half a mile below the surface just a few hundredths of a second after impact. This compressed the rocks all around to a quarter of their size. It was the resulting explosion, caused by this compression, that did all the damage. The energy released was 250,000 times greater than the atomic bomb that devastated Hiroshima. it scooped out a hole 2 miles deep and generated a mushroom cloud 19 miles high. A large amount of material was ejected ballistically in every direction. The mushroom cloud, full of melted bedrock (and what little remained of the asteroid), fell back violently to the ground – a deadly rain of material similar to a volcanic pyroclastic flow. Altogether, 250 cubic miles of rock were moved by the explosion, equivalent in scale to the Yellowstone supervolcano eruption 600,000 years ago. Large boulders have been found 40 miles from the impact center. Some small pieces of the melted bedrock even returned to Earth 250 miles away, in an area now part of the Czech Republic.
For 60 miles in every direction, life simply ceased to exist. The extremely high temperature shockwave saw to that. Trees all over Southern Germany would have been uprooted by the shock wave. The scale of the explosion greatly exceeds the threshold for a global nuclear winter, so it is possible that the world’s climate experienced sudden and temporary cooling as a result of the impact.
But life, tenacious as always, re-established itself in the region. A large lake was formed. Animals and plants returned. Over the intervening millennia, sedimentation and glaciation flattened out and smoothened the region in to the geological feature we see today. Nowadays this area of Germany is known as the Ries: a circular plain 15 miles in diameter, comparatively flat and circular compared to the surrounding hilly countryside of the Swabishe Alb.
The smaller impact crater in Steinheim also became a lake, but its features as an obvious crater site are much better preserved. It has a distinct central uplift upon which the small town of Steinheim am Albuch is located.
As early as 1792, questions began to asked about the Ries’ origins. Naturally enough, most people believed that it was volcanic, as volcanism is not unknown in this region. Questions surfaced however as to the non-volcanic character of the widespread debris field around the Ries. Despite this, the volcanic interpretation persisted until the 1960‘s, with some quite creative hypotheses being postulated to explain away the anomalies. Then along came Gene Shoemaker and Edward Chao, two American astrogeologists. They detected Coesite or “shocked quartz” in the immediate region of the Ries. They concluded that the Ries was a meteorite impact site, given that this material only occurs in the presence of extremely high pressures and temperatures – much higher than volcanism can ever generate. The Ries quickly became famous among the astronomical community, as it is regarded as one of the best preserved large impact craters on the planet. NASA moon astronauts were sent there in 1970 to learn as much as they could about the formation and geology of large craters. Information from the Ries contributed greatly to the discovery during the 1980’s of the Chixulub impact site, linked to the extinction of the dinosaurs.
The steeple of St Georg’s Church in Nordlingen, or the Daniel as it is called locally, offers the best possible view of the entire crater expanse. Looking around at the flat plain with the low hills in the distance gives you pause to consider. This feature, the dominant landform on so many of the rocky moons and planets of our solar system, is a rare enough sight on the surface of our own planet. It’s possible to imagine yourself on the Moon, or Mars, looking at a similar vista stretching into the distance. This view makes you realize that we are not so unlike our neighbors in space as we might imagine ourselves to be. We are vulnerable to giant impacts too.
The walled town of Nordlingen is peaceful, pretty, orderly. Walking around the town, it is hard to believe that it was the epicenter of such utter devastation as hit Germany 15 million years ago. If anything, it is a stark reminder that large asteroids can intrude on the planet in an instant, changing everything in seconds. They have happened in recent geologic history and will certainly happen again.
End of podcast:
365 Days of Astronomy
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