Chemistry: Matter and ChangeChapter 26: Chemistry in the EnvironmentIn the NewsAtmospheric Chemistry--but Whose Atmosphere?October 2004It was only some four hundred years ago that a philosopher named Giordano Bruno speculated that there may be countless other worlds in the sky with countless other living things on them. As a result, the church burned him at the stake for heresy! It's ironic that today, most scientists who study the heavens assume Bruno's suggestion to be correct. We call those “other worlds” extrasolar planets, or planets orbiting stars other than our own. As for living things out there, we have no direct evidence for it yet. Still, many scientists also assume that alien life exists--indeed, that life of various sorts can probably be found all over the Milky Way. Of course, that doesn't necessarily mean advanced alien civilizations with floating cities and moon bases. But then, it could; we really don't know what shape life has taken on other planets. In fact, until just recently, it didn't seem possible to know. Extrasolar planets are just too far away to go there and see. But new technology is being created right now that is letting chemists right here on Earth check out alien worlds . . . and even scan them for evidence of life. Atmospheric Chemistry How can we do such a seemingly impossible thing? By understanding atmopsheric chemistry. That term means just what it sounds like: scientists now know a good amount about what kinds of chemical processes on a planet produce what kinds of atmosphere. For example, our atmosphere is rich in oxygen. That seems commonplace to us, but it's actually kind of odd. Why is that? Because oxygen combines with rocks, so you wouldn't actually expect a lot of “free” oxygen to be floating around. In order to have an oxygen-rich atmosphere, you need something that keeps producing more oxygen. What do we have on this planet that does that? You got it: plants. That's one way the metabolic cycles that plants and animals go through have an effect on the atmosphere itself. In fact, in all sorts of subtle ways, the presence of living things here alters the chemical composition of the air all around us. So, in principle, we could tell a lot about alien planets just by doing some atmospheric chemistry on them. But since even the closest stars are light years away from Earth, how can chemists here possible analyze atmospheres way, way out there? Answer? Starlight. Chemistry by Starlight The idea is this: the light from a distant star is shining at Earth. That's why we can see the star. That light is largely unimpeded, unless a planet circling that star happens to get in the way. When that occurs, we have a terrific opportunity, because we know that some of the light coming to us from that star is now passing through the atmosphere of the alien planet. The atmosphere, depending on its composition, will allow some kinds of light through and not other kinds. If we can tell the difference between what the starlight contains when the planet is behind it and what it contains when the planet is in front of it, we can tell what the planet's atmosphere is made of chemically. This sounds incredible, but with modern telescopes and computing power, it's possible. In fact, it's already been done. In 2001 the Hubble Space Telescope made the first observation of the chemical sodium in the atmosphere of a distant planet as it passed in front of star HD 209458. That's a start; we know the process works. Now, the dream of many starry-eyed chemists on Earth is to refine this process until we can check out extrasolar planets one by one, examining their atmospheric chemistries in detail. And who knows? Maybe one of them will show a little biology, too . . . Activity: Take a walk around your neighborhood today, or through some nearby woods if you can. Keep your eyes open for evidence of living things. What traces are left behind by life? How do living things alter the environment they live in? See if you can find ten examples of things that wouldn't be the way they are if not for the presence of life. Finally, see whether you can spot specifically chemical changes that are taking place right now because of living things. NASA: ABC News: Reactive Reports: Chemistry Web Magazine: Center for Atmospheric Chemistry: Looking Forward to the PastMarch 2005A lot of scientists--and smart people in general--are concerned about global warming. That's the trend toward increased temperature our planet is experiencing, largely as a result of things we humans do. Burning fossil fuels, such as oil, puts chemicals into the air which change the atmosphere. Gradually, this changes other things, too, from how high or low the oceans are to how strongly the winds blow to plenty of things we don't yet understand. How might the climate react if we keep on affecting the atmosphere the way we are? Scientists would like to know--but how can they predict the future? Actually, there are ways. One way is to look into the past. Deep Ocean Cores In order to help them think about these issues, chemists at the University of California, San Diego and Stanford University have managed to look back into Earth's past . . . 130 million years back, in fact. They wanted to see what things were like during previous periods in our planet's history in order to get a sense of how the climate changes. How can you examine the ancient past without a time machine? By drilling up deep ocean cores. Ocean cores are long, thin rods of matter drilled from the floor of the ocean. If you've ever cored an apple, you have a sense of this process already. You insert a tube-shaped blade into the apple, push it all the way in, and pull out a long, thin section. It's the same idea here, although ocean cores are much larger than an apple core. Cut the Cake Once the cores have been brought up to the surface, they can be examined for the presence of various chemicals at different spots. Why do that? Because the floor of the ocean is like a time capsule: since sediment is laid down across time, the deeper you dig, the older the sediment you're seeing. Imagine slicing into a big birthday cake and then examining the side of the slice. You'd see layers. The bottom layer was made first; then some icing was put on it; then another layer of cake was added; and so on. So the bottom of the cake is older (by a few minutes, anyway) than the top of the cake. Deep ocean cores are like that, only the very bottom is 130 million years older than the top! Quest for Sulfur These chemists were especially interested in the presence of sulfur along the cores they dug up. That's because different types of sulfur are laid down on the ocean floor under different conditions. A lot of sulfur of a particular type *here* means there were volcanoes going off during *this* period (and chemicals they blasted out eventually sifted into the oceans); a lot of sulfur of another type *here* means lots of continental weathering was happening during *this* period, and so on. By learning these things, the chemists could infer what the atmosphere on Earth was like at different times, how long those conditions lasted, and more. Quick Changes What does this have to do with global warming? By looking into this long-buried record, the chemists were able to see when climate changes have occurred in our past. Were oxygen levels going up or down? Were the glaciers freezing or melting? When? For how long? Once they knew these things, they had some direct evidence on which to base their theories of how the climate behaves. One of the more sobering insights the researchers gained from this work is that things can happen pretty quickly. That means the changes we are causing to our planet's atmosphere--which are already making the glaciers melt, for example--may have serious effects sooner than we had anticipated. “Some relatively rapid changes can happen on Earth,” says Adina Paytan, the first author of the report that came out in Science magazine in June. “So we have to be prepared.” Activity: If you have access to a refrigerator (other than the one your family uses!) that has a dial for setting the temperature, ask your parents whether they will help you with an experiment using it. Try keeping some food items in this refrigerator for a week, taking notes on how well it preserves things. Next, then turn the dial down by one degree for one day, and see what happens. You wouldn't think that a one-degree change would make much difference, but does it? Take more notes, examining everything in the refrigerator before and after you change the temperature. What has been affected? What surprised you? (If you have liquids in your refrigerator, be careful--liquids expand when they freeze and can break out their containers, leaving you with a goopy mess.) UCSD: Science Magazine: Paytan Chemical Oceanography Lab: |  |
