November 5th: Earth and Sky: Together at Last! Part 2

Date: November 5, 2009

Title: Earth and Sky: Together at Last! Part 2


Podcaster: Alan Perkins

Organization: Department of Geosciences at San Francisco State University:

Description: The disciplines of astronomy and geology, which used to be separate, are working together in the new field of planetary science. The episode also discusses how discoveries in astronomy and geology are useful in the study of the other field. Examples might be how geology assists in the understanding of other celestial objects, such as Titan. On the other hand, knowledge obtained through the study of astrophysics, for example cosmic rays, is useful to geologists in dating geologic processes on earth. The content is conveyed through an interview of Dr. Leonard Sklar of the Department of Geosciences at San Francisco State University.

Bio: Alan Perkins is an amateur astronomy/planetary science enthusiast. Dr. Leonard Sklar of the Department of Geosciences at San Francisco State University.

Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by Clockwork Active Media Systems. Clockwork invents, designs, develops and maintains web applications that market, sell, streamline, automate, and communicate. Visit clockwork dot net or email inquiries at clockwork dot net to get started on your web project.


Alan Perkins: I’ve heard the synergy of geology and astronomy is really a two-way street. Has the study of astronomy and astrophysics provided some useful techniques for the study of the earth?

Leonard Sklar: Oh, yes, for sure. I mean, one of the reasons that we go to study other planets is so that we understand our own better. But, for example, testing the model that I’ve developed for river incision into bedrock on Titan confronts us with the limitations and forces us to understand better the physics here on earth when we’re trying to explain what happens on some other planet.

But in terms of techniques there are many, many ways that astrophysics and the study, trying to develop both techniques and insight for how things work outside of earth, helps us here on earth.

One example is a very powerful dating technique called cosmogenic radionuclide dating that has revolutionized our understanding of the rate at which earth’s surface processes shape land forms.

And what this is, is an understanding from astrophysics of the flux of high energy particles that come in from other stars and even from other galaxies and there’s a rain of these particles that enter into our atmosphere and actually pass through our bodies even. When these particles, these charged particles, hit the atmosphere it actually creates a kind of complicated cascade of interactions in the atmosphere that makes a rain of these minute particles.

But the key thing that happens is when they strike the nucleus of an atom, for example, in a quartz grain, in a rock, they cause a reaction that forms an isotope that’s unstable. And that unstable isotope will decay at some known rate.

And so what we can do is we can go and take a sample of rock and dissolve and do quite extensive work on it in the lab. But eventually put it in a big machine where we can count the number of atoms that are produced by this process of the impact of the cosmogenic rays striking the nuclei and from that estimate how long the rock has been at the surface of the earth, because the influence of these reactions only happens right at the surface. It’s about a meter deep. The rate decays to a very negligible rate.

So you can think of this as a kind of a cosmic sunburn that the rocks receive and by how burned they are, or how unburned they are, if you like, we can work out how long those rocks have been sitting at the surface.

And from that we can work out how rapidly the surface is eroding. And that’s a super useful thing to know to try to infer how landscapes evolve and how they respond to the forcing from tectonics or from climate or how different rock types – at the rates that rock types erode. And as I said, this has really revolutionized our study of land forms on earth.

Alan Perkins: One question I have is if you don’t know how fast or how much or – volume, I guess – of cosmic rays are coming, how do you know that technique is accurate?

Leonard Sklar: Well, people have studied this a great deal. And so we now have a good idea of if you were outside the earth’s atmosphere what the rate of cosmic rays would be that you would experience. And the key thing is to know how that’s attenuated by where your place of interest is on the earth.

And so the thickness of the atmosphere matters and so elevation matters. So if you’re on top of a mountain you’ll be feeling – you’re more likely to get this cosmic sunburn than if you’re down at sea level.

And also the earth is in a plane orbiting around the sun which is also similar to the plane of our galaxy. And so the orientation of where you are with latitude, if you’re close to the pole versus being close to the equator also influences the flux.

And so when you take a measurement, you take a rock back to the lab, in the field at your site where you’ve sampled, you need to measure – you need to know your elevation, your latitude, but also you need to measure how much topographic shielding there is.

So if you’re in the shadow of a big mountain that’s going to reduce the flux of the cosmic rays. But there are well worked out techniques to do this.

Alan Perkins: Wow. Well, thank you. So in the future both astronomy and geology seem to be integral parts of the study of other celestial bodies. Does that mean that some fields of geology give a student a chance to use one set of skills to study both the earth and other bodies?

Leonard Sklar: Oh, very much so. It’s such an exciting time to be a geologist because of the influence of astronomy and the growth of the field of planetary geology.

So many problems that we are trying to understand on earth have analogs in trying to understand other planets. You know, for example, the question of how do you get valleys that have a sort of amphitheater shape to them has been a subject of a lot of recent study, and I’ve taken students on field trips in Southern Utah to go look at these features.

They’re very beautiful and compelling cliffs of red rock that have topographic analogs on other planets, for example, on Mars. And the classic interpretation of Mars, you know, people looking through telescopes at Mars was that these must be formed by water seeping out of the base of the cliff.

But we – here on earth we have examples of the same features that people made the assumption were formed by this seepage process, but when we’ve gone deeper to look at “Well, what are the exact mechanisms by which the particles are detached due to seepage and what are the alternative explanations that might be out there?” we find that more conventional river flow, water spilling over the edge of the cliff, is capable of creating these land forms as well.

So in Utah, there’s another place in Idaho, where students have gone to look at these box canyons, they stand there and are confronted not only with the question of, “How do things work on earth?” but “Could this be the way things work on Mars as well?”

Alan Perkins: What might be a typical curriculum in the U.S. for a university undergraduate who wanted to major in geology leading towards further study of planetary science?

Leonard Sklar: Well, there’s many ways you could go. Of course, the more math and physics a student has the more readily available the techniques and the whole fields of disciplines in geophysics and in astrophysics and so forth become available.

But I tell students who are interested in this that they should follow their curiosity and follow their passion. And so, you know, the study of sedimentology, for example, has application on planets. You know, for example, the Mars rovers have been sending back images from craters where we can see sedimentary structures in the crater walls.

Geomorphology, you know, my own discipline, is an excellent place to pursue one’s curiosity and passions for both understanding the earth and other planets.

So a conventional geology curriculum or one that has a stronger quantitative element of mathematics and physics and chemistry as well, either way could be a good path to further study and a career in planetary science.

Alan Perkins: Do you have any recommendations for websites or other references for people who wants to learn more about pursuing a career in planetary science?

Leonard Sklar: Oh, there’s a wealth of information on the web, so many great places to go. Of course, NASA has many excellent websites. I’ve certainly been inspired by the astronomy picture of the day site which has everyday a different image with many, many links. And some of those will lead back to planetary science.

There’s the International Association of Geomorphologists has a division of planetary geomorphology. They’re at the American Geophysical Union meetings, there’s a section on planetary geology where – so the American Geophysical Union or website is a good place to go to find more scholarly abstracts and so forth.

There are many researchers and good groups – research groups to pursue at Cal Tech, at Arizona, at Brown University. There’s another fantastic website has been created by a geomorphologist named Alan Howard at the University of Virginia.

Alan does numerical modeling, among other things, of the evolution of earth’s surface and planetary surfaces, and has some fantastic animations of calculated evolution of Mars and of the moon and of other planetary bodies.

Certainly the web is a fantastic place to find good connections. But I also would encourage people who are interested to directly contact other scientists, scientists such as myself or people researching in this field. You’ll find that geologists and planetary geologists are eager to talk about their field and delighted to share what they know with anybody who’s interested.

Alan Perkins: Well, Dr. Sklar, you pointed out that many professional scientists like you are extraordinary giving of their time to help people learn more about science. We appreciate your giving your time today to help the International Year of Astronomy. Thank you again for joining us.

This concludes today’s episode. We hope you look forward to future editions of the “365 Days of Astronomy” podcast.

End of podcast:

365 Days of Astronomy
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About Alan Perkins

Alan Perkins is an amateur astronomy/planetary science enthusiast. Dr. Leonard Sklar of the Department of Geosciences at San Francisco State University.

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