Rare meteor crash site discovered in Minnesota

CATHY WURZER: There are fewer than 200 confirmed meteorite crash sites in the world. In just the past week, the University of Minnesota has found one in Dakota county. Jim Cotter is a professor of geology at the university of Minnesota, Morris. Every month on the program, Professor Cotter tells the story of our state through geology, and he is back. Hey, Professor. How are you?

JIM COTTER: I'm good, Cathy. It's nice to be back.

CATHY WURZER: Oh, I'm glad you're here. Thanks. So I bet you were pretty excited about this. I understand this crash site was discovered buried several 100 feet, buried beneath Inver Grove Heights. How does one find a meteorite crash site?

JIM COTTER: It's a good question. One of the things our planet is very good at is hiding landforms. And when a meteorite hits, of course, it makes a very, very distinctive landform. But through processes that everyone's well aware of, running water, glaciers, landslides, that stuff gets obscured, obliterated. And in the case of this site, the Pine Bend Impact, it got buried. And so they are relatively hard to find.

CATHY WURZER: According to reports, the geological survey here in Minnesota discovered this crash site, as I mentioned, several 100 feet below Inver Grove. I don't even know how you start looking for something like that.

JIM COTTER: It really is just something you have to applaud. Julia Steinberg I think was the lead scientist on the work, but the whole Minnesota Geologic Survey really did some very nice work.

What they were doing was part of their county map system. They're systematically going through the state and mapping individual counties to look at rock types, possible resources, water resources, and maybe something that might be sensitive to environmental impact. So it's a very systematic approach they're taking.

And when you're doing something like that and depending on what's exposed on the surface, you depend a lot on drill course. And so well drillers and professional drillers will drill down and pull up rock samples. And so literally, you're feeling your way through the depths and looking at samples that come up in the shape of a core. It looks like a big straw almost, maybe four or five inches across. And you extrude the rock and then you start looking at it.

So you don't have a complete sense of anything that's more than a couple feet away from that exact point that you've drilled the core. And so when you start seeing interesting things, there are a couple of things you could do. You say, well, that's weird and then forget about it. Or you can say, I'm going to keep my eye out for more of that. And I think that's what the folks at the survey did. And they started seeing something very, very unique. And as a result, you get this great discovery.

CATHY WURZER: Is this called-- is it the unique finding shocked quartz?

JIM COTTER: There's actually a couple unique findings. One is that for anybody who lives in the Twin Cities or south of the Twin Cities, they're used to seeing rocks in layers. And the layers in southeastern Minnesota are relatively undisturbed. They're flat.

And what they started seeing were the layers being not only tipped and standing straight up, but also turned over completely. And then turning over thousands-- not thousands, but hundreds of feet of rock is a pretty significant event. So there's a disturbance there that they recognized.

And then they kept looking in greater detail. And what they found were shocked quartz. And that is really, really good evidence that the disturbance, the things that move the beds around was an impact event.

CATHY WURZER: Wow. So scientists date this crash site to about 490 million years ago. What was going on back then?

JIM COTTER: It was a spectacular time in Minnesota. I was going to talk about it one of these weeks. Minnesota would have been at the equator. And I was saving this one for cold weather, where we could talk about the equator.

Minnesota was at the equator, and north America was rotating in a clockwise manner towards Europe. And what happened was that the equator would have run parallel to the Western border of Minnesota. So it tapped on its side.

And the state and most of the country was covered by this beautiful equatorial ocean. And it was just at the beginning of abundant life. So there's really interesting animals that exist at the time, trilobites, people are aware of are beginning to flourish, and brachiopods, and animal with two shells that are not mirror image. And relatives of squids, Ammonites, are starting to come in.

And it just would have been a beautiful sight to see. Went out of the sky 490 million years ago comes this impactor. So it was-- it would have been just an amazing, and if you were nearby it, catastrophic. But it was a beautiful time in Minnesota.

CATHY WURZER: When you see the catastrophic, it was, I believe, two-and-a-half miles in width. So yeah, that would have made quite an impact obviously.

JIM COTTER: Yes.

CATHY WURZER: And so that's the name these craters-- these impacts for where they were found, right?

JIM COTTER: Yes, that's a geology tradition. You name something after the locale where you find it.

CATHY WURZER: So this will be the Pine Bend Impact site?

JIM COTTER: That's right.

CATHY WURZER: Wow. Well, what else was exciting for you when you read the article about this impact site?

JIM COTTER: So for-- I must admit, as I get older, I start thinking about the future. What a discovery-- not just this one, but this one is a good one. What a discovery does is bring up more and more questions.

And so the beginning of the Ordovician is a time of extinction. And if this coincides with the date they're suggesting, 490 million years, the question is was this part of an extinction event?

The other thing is how wide an impact? So the entire North American continent was under a shallow ocean at the time this thing would have hit. How far can we trace the tsunami that would have been generated by this impact?

And the great thing about it is that there'll be young men and women reading about this and hearing about it in classrooms and colleges and high schools in Minnesota. And they're the ones who are going to answer the question. So it's--

CATHY WURZER: I love that.

JIM COTTER: --really exciting stuff.

CATHY WURZER: Professor, always fun talking to you. Thank you so much.

JIM COTTER: Yeah, happy to be here. Thanks, Cathy.

CATHY WURZER: Jim Cotter is professor of geology at the University of Minnesota, Morris.