Sharp eyes of geologist find meteorite debris from Sudbury crater in Minnesota

William Atkins
Monday, 16 July 2007 22:20

Science - Energy

The Sudbury Basin is located near Greater Sudbury, a city in Northern Ontario, Canada.

Mark Jirsa, a member of the Minnesota Geological Survey, was the geologist who first found evidence of the debris while hiking along the Gunflint Trail near Ham Lake in northeastern Minnesota. He was on a field trip at the annual meeting of the Institute of Lake Superior Geology when he discovered the important geological find.

The exposed debris was able to be more easily seen after a large and damaging fire went through the area in 2007. The debris found by Jirsa consisted of darkish looking rocks that have a composition look of concrete and were found in all shapes and sizes.

The second-oldest meteorite impact crater, also known as the Sudbury Structure, is about 1.85 billion years old. At about 39 miles (62 kilometers) in diameter, the major geologic structure is also the world’s second-largest impact crater to have ever been discovered. Today, the impact crater is about 9 miles (15 kilometers) deep.

Its diameter is much smaller than when the meteorite first hit. Geological processes over the past 1.85 billion years modified the shape of the impact crater. It is estimated that the original depression was about 155 miles (250 kilometers) in diameter. It was formed when a 6- to 12-mile (10- to 20-kilometer) meteorite impacted the Earth’s surface.

The meteor—which is any type of small sized space debris, but in this case assumed to be either a comet or an asteroid—had a speed of about 12 to 37 miles (19 to 60 kilometers) per second before it hit the Earth's surface. Temperatures skyrocketed 10,000 degrees, causing rocks to melt and forming the crater. Rocks and dust particles traveled over 500 miles (800 kilometers) away in all directions.

The 186-mile (300-kilometer) diameter Vredefort Crater in South Africa is considered to be the largest impact crater on the Earth, while the Chicxulub Crater in Yucatan, Mexico, is considered the third largest impact crater.

From the article “Big fire, big hole, big discovery” within the Duluth News Tribune (July 15, 2007), Jirsa said, “There’s a lot of work that needs to be done in the field to see what this deposit tells us that other sites don’t. That’s the critical thing. This is a different geological setting; it’s a little farther away from the impact, the rocks are altered differently. It may reveal some secrets about the impact that other discoveries haven’t yet. That’s what we’re hoping.”