IRA FLATOW, host:
For the rest of the hour, we're going to talk about the Grand Canyon. You know, there's the Grand Canyon's in the news this week because there're hundreds of thousands of gallons of water per second rushing through the Grand Canyon to try to clean it out and restore a little bit to where - the state it used to be before the dam was built there.
But if you take that tour of the Grand Canyon, the tour guide inevitably will get asked and you probably have been there, just how old is this big hole in the ground? And the official guide tour answer is usually, oh, around six million years old. But new research out in today's issue of the journal Science, puts the age of the canyon at about 17 million years. That's 17 million. That's several million years older.
And according to the researchers, the older age come from a new dating technique that enabled them to study how water interacted with cave formations; cave formations that were present when the canyon was being carved. But not everybody agrees with their assessment - some scientist say that the new dates don't mesh with the geologic evidence for the Grand Canyon's age and formation.
One of the lead authors on the Science paper is here to make the case for a much older Grand Canyon, and address those criticisms. Victor Polyak is a senior research scientist at the University of New Mexico in Albuquerque. He joins us today from his office.
Welcome to SCIENCE FRIDAY.
Dr. VICTOR POLYAK (Geologist, University of New Mexico): Well, thank you, Ira.
FLATOW: Why is your age so much older than the older age?
Dr. POLYAK: Well, we don't know why it's older.
(Soundbite of laughter)
Dr. POLYAK: We did our research and that's what we came up with.
FLATOW: Let's walk through the sequence of events that you think occurred. Tell us how in your research, you think, the Grand Canyon started, and it involves more than one river that we have there, the Colorado, but two other nameless rivers.
Dr. POLYAK: Well, we call for possibly a smaller river system working on the edge of the Colorado plateau from 17 million years ago to, you know, perhaps six million years ago. Working a canyon headward, or eastward in this case, slowly. So we called for that because we know that it's well established that the Colorado River system was through flowing about six million years ago. So before that, you didn't have a through-flowing system, so there must have been something there cutting the canyon.
FLATOW: MM-hmm. And what evidence do you use? What new evidence do you have for the…
Dr. POLYAK: Well, we approach the problem of the age of the canyon through the caves of the canyon. And one of the problems with determining the age of a canyon is that the processes that form canyons tend to remove its evidence of origin.
FLATOW: Sweeps it down river, so to speak.
Dr. POLYAK: Right.
Dr. POLYAK: And so, except close to the river where scientists have some good date on incision rates in the canyon, in two areas at least.
FLATOW: So, you went down into the caves that were there as the water level dropped down?
Dr. POLYAK: We went - what we did is we started a study of the caves in the canyon about 10 years ago, and we identified at least four cave deposit types. The cave deposits are called speleothems. So, four speleothem types that are related to groundwater tables, and one of them is called a cave mammillary, or mammillary coatings, and these are coatings on the cave walls that form close to the water table.
And so we knew, by visiting these caves, that if we could date these materials then we could place the position of a pre-existing water table at a particular place at a certain time in the canyon.
FLATOW: And so you basically rappel down the side of those canyon walls?
Dr. POLYAK: We had to do that in some cases. We had a lot of climbing to do. And Carol and I are - the co-author Carol Hill and I are both cavers. We're experienced cavers. But getting off trail in the canyon can be very dangerous and getting to these caves can be very dangerous. So, we surrounded ourselves with expert cavers and climbers to help us get to these caves.
FLATOW: So when you saw the layer in the caves, how did you date that layer?
Dr. POLYAK: We used a - it's not a new process, it's a process called uranium-lead dating. And it's been improved greatly over the last 20 years or so by the use of mass spectrometers, so we're able to do a better job of dating younger materials now because of those advances. So we had the opportunity to apply this to these calcite deposits in these caves in the canyon.
And what's nice about the caves is that, you know, they were there. They were there before the canyon formed, and so they have deposits in them that pre-date the canyon deposits that were deposited while the canyon was forming and those that were deposited after the canyon, after the water table dropped down through the caves.
FLATOW: And so you pushed the date back to 17 million years?
Dr. POLYAK: Yes. Our oldest date was from a commercial cave just outside the canyon called Grand Canyon Caverns, and we have a uranium-lead age on that calcite of 17 million years. Today, it's 1,200 meters - I think it's 1,200 meters above the river.
And so, just assuming a relatively flat water table, you know we can calculate an incision rate over that time period. And we have that age pretty early but we needed - when we got our first couple of dates, our first results, we applied for a grant with the National Science Foundation and we got it, and we were able to do a lot more work once funded. And we filled in some gaps since then, so now we have four dates on the western end of the Grand Canyon, and they're spread out vertically.
So the closest one to the river is - should be the youngest in the western Grand Canyon. That sample was about two million years old, a little over 100 meters above the river. And so all of those samples in the western Grand Canyon showed that the groundwater table had to be dropping steadily over the last 17 million years.
FLATOW: Uh-huh. 1-800-989-8255, let's go to the phones. Dr. Luchita(ph) from Flagstaff.
Dr. LUCHITA (Caller): Hello.
FLATOW: Hi there.
Dr. LUCHITA: Hi. How are you doing?
Dr. LUCHITA: Alright. I would like to make a couple of comments.
FLATOW: Well, quickly.
Dr. LUCHITA: Quickly, all right, I'll do my best. In many years, 45 years of working on the Grand Canyon, I've learned that rivers are very hard to trace directly so you have to use indirect evidence. Of this indirect evidence, there are 80 years worth of very useful data that bear on the problem. Many of these, or I would say even most of these pieces of evidence contradicts the hypothesis presented by these people on this paper. And…
FLATOW: What evidence in particular?
Dr. LUCHITA: Would you - well, do I have time?
FLATOW: No. Give me - to present a piece of evidence, I think so.
Dr. LUCHITA: Okay. Let me, for example, tell you that before - okay, I have to set the stage a little bit.
Dr. LUCHITA: See that's the problem.
FLATOW: Okay. You can't tell me what the evidence is. Okay.
Dr. LUCHITA: I can tell you what the evidence is. There's a lot of it. And basically there's no evidence for Grand Canyon in the western Grand Canyon until about six million years ago, and it's of many different kinds, including most notably the fact that's in the big trough just beyond the mouth of the Grand Canyon, which was filled with material coming from the west. But there's no evidence of any kind of a river deposit or anything else like that until after six million years ago. Had there been a Grand Canyon, had there been a river, you should see some evidence.
FLATOW: You'd see a lot of debris coming out of the Grand Canyon.
Dr. LUCHITA: Correct.
FLATOW: Dr. Polyak, can you answer that?
Dr. POLYAK: Well, I would start by saying that we have direct evidence to work with, and I'm not - it's a - it could be a problem. But, for instance, there's one deposit just at the mouth of the Grand Canyon called the Hualapai Limestone, and it fits our model pretty well. It's a large carbonate deposit, a lacustrine(ph) deposit. And it could explain, you know, it matches our groundwater table dropping down through the carbonate units in the western Grand Canyon, and that could explain how that deposit formed.
Dr. LUCHITA: Right. But the Hualapai is pretty late. It's not 17 million years old at all.
Dr. POLYAK: Well, the top of it is…
Dr. LUCHITA: Right.
Dr. POLYAK: …five or six million years old.
Dr. LUCHITA: Right. And I, you know, I studied that for my dissertation and it starts out by being very small, playa-like deposit, and with time, it gets bigger and bigger. And it only gets large towards the end, about six million or thereabouts.
Dr. POLYAK: Right. And that does fit our theory.
Dr. LUCHITA: But not 17 million.
Dr. POLYAK: Not 17 million. But by the time the canyon cuts down into the carbonate rocks, you know, 10 million years or so up to recent, you know, that's a source of a lot of carbonate material that would explain…
Dr. LUCHITA: Sure.
Dr. POLYAK: …the Hualapai Limestone.
FLATOW: All right. Let me interrupt and say this is TALK OF THE NATION: SCIENCE FRIDAY from NPR News. I'm Ira Flatow, talking with Victor Polyak of the University of Mexico in Albuquerque.
And then, Dr. Alva Luchita(ph), is that…
Dr. LUCHITA: Luchita.
FLATOW: Luchita. And you're with?
Dr. LUCHITA: Well, I'm a U.S. Geological Survey, retired, and emeritus.
FLATOW: Okay. So, okay, that was issue number one. Have you got another issue that - very nice succinct one.
Dr. LUCHITA: Yeah. The statement was made that they have direct evidence for the formation of the Grand Canyon. Well, I would submit that all things going swimmingly with the technique and everything else, they do not have evidence for the Grand Canyon. They have evidence for lowering of the water table. And I would submit that this big hole to the west of the Grand Canyon, which was formed by faulting starting, maybe, 17 million years ago - interesting the coincidence of the numbers - would be a wonderful place to start draining the edge of the Colorado Plateau because now, you've got the dam, you got a huge cliff, and groundwater is going to start draining into this big hole. And it would start doing that 17 million years ago or thereabouts whether there was a Grand Canyon or not.
FLATOW: Dr. Polyak?
Dr. POLYAK: Well, we have no problems with the different interpretation from our data, but at some point, you have to integrate what the canyon that's there today…
Dr. LUCHITA: Sure.
Dr. POLYAK: …well, you have to have some evidence of this pre-existing canyon.
Dr. LUCHITA: Well, we say that there wasn't a canyon until about six million years ago or thereafter. But you could have had groundwater leaking into the Grand Wash trough, canyon or no canyon.
Dr. POLYAK: Yeah. That would be - it seems like there should be some evidence of that because that's a lot of water.
Dr. LUCHITA: Well, yeah, not really, you know, you had interior basins. There was not much evidence that, in fact, we know there were some small drainages that emptied into that trough, and they have left plenty of evidence of themselves, far smaller than any Grand Canyon or Colorado River. So, we know that drainages existed and they left a signal. But at the mouth of the Grand Canyon, we see no signal at all.
FLATOW: I would have to end this debate. Thank you very much for calling.
Dr. LUCHITA: Okay. Thank you.
Dr. POLYAK: Thank you, Ira. Bye.
FLATOW: You're welcome. We have - many years ago, on SCIENCE FRIDAY, we first went on the air 18 years ago, people are wondering, I can't believe I heard scientists disagreeing with each other on the radio. So this is just another bit of evidence like that. Dr. Polyak, are you still with us?
Dr. POLYAK: Yes, still with you.
FLATOW: Where do you think now do you go with this research? Do you try to cement it in a little better, so to speak, with more evidence?
Dr. POLYAK: Oh, we absolutely do, yes. We're going to continue with our research and we're excited about it, and we think it's a step forward as far as changing the thinking about the Grand Canyon. And we think there are hundreds of these deposits scattered throughout the Grand Canyon that will hopefully tell us more about it.
FLATOW: And I'm sure you're not surprised by the reaction that you've been getting.
Dr. POLYAK: No, we're not surprised. No. I have great respect for all of these people who worked on the Grand Canyon. And we're not surprised by the…
FLATOW: All right. Well, we'll keep watching your research and your evidence for the Grand Canyon, and hopefully we'll have you back on soon with some more work.
Dr. POLYAK: Okay.
FLATOW: Thank you very much for taking time to be with us.
Dr. POLYAK: Thank you, Ira.
FLATOW: You're welcome. Dr. Victor Polyak, senior research scientist at the University of New Mexico in Albuquerque.
Well, we've run out of time.
If you'd like to surf over to our Web site, we're podcasting and blogging and we have new videos up there. You can see some videos that Laura(ph) put up today - looking for your videos, maybe you live by the Grand Canyon. You're up there, you have some ideas about your own ways the Grand Canyon were formed. You got a video you'd like to make, send them to us, we'll take a look at them, judge them and maybe put them up on our site or videos about any other kind of science that you're involved in. Maybe you're a researcher, you got some videos of what you're doing in the lab, send them to us. You'll see some of them already up on our site right there, right now.
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I'm Ira Flatow in New York.