Let’s say the length of your arms stretched out is the history of Earth. Then you take a nail file and rub your furthest fingernail. You’ve just removed all of human history. That’s one of writer John McPhee’s analogies for geologic time that I use when I’m teaching. But the truth is that the scale of geology is so much bigger than the human experience that it’s hard to wrap your mind around it. And at the time I was first introduced to it, there were distractions.

There was only one other girl in my class. I wasn’t dating anyone in particular and didn’t really want to. It soon became clear to me that it was considered weird to be a single woman who wanted to study rock formations, of all things. I felt like I was on the defensive at a time when I wanted to be open to all that I was learning.

It was stressful, so on geology field trips to the mountains around Chandigarh, I often went off on my own and sketched. The hardest part of sketching mountains, especially the Himalayas, is getting a sense of scale. You can put on paper only little vistas of what you see here and there. And what you see from one vantage point changes completely when you go to another.

There I was, in the fall of 1989, plopped down in the middle of this country, where there are no mountains. It was a bit of a shock, but it probably didn’t matter where I lived because I always seemed to be up for three nights in a row, studying to catch up. I hadn’t had access to the latest textbooks in India. There was so much I didn’t have a clue about. One day, a faculty member, Ghislaine Crozaz, asked me, “Would you like to see a piece of Mars?”

It may be hard for you to imagine what it was like for me to hear those words at that time. I was 21. I knew about the manned Apollo 11 moon landing in 1969, but I didn’t know how many there had been after that, or that hundreds of kilograms of moon rocks were available to be studied. So my reaction was, “Whoa! You actually have a piece of Mars?”

She explained that some large impacts had most likely occurred there and chucked pieces of Mars’s crust into space, and that they eventually fell to Earth. The first piece of Mars I saw was a very thin slice that we looked at under a microscope. Most scientists who study meteorites believe that this sample came from Mars because the gases trapped in it have the exact same composition as the Mars atmosphere—a very distinctive composition that was determined by the Viking spacecraft in 1976. The section must have been about 30 microns thick—a micron is one thousandth of a millimeter—and at that level the minerals are essentially transparent. When polarized light is passed through them, you can see brilliant colors—reds and greens and yellows and blues that are diagnostic of the different minerals.

It was beautiful, but it was strange because it wasn’t weird. In fact, it was a little disappointing because the sample looked so much like Earth rocks that I’d seen. Then I thought, “What can you learn about the history of this other planet that’s supposed to have evolved so differently from ours, yet was able to produce this rock that looks so familiar?”

From that moment on, there was no pulling me away.

Professor Crozaz was using state-of-the-art equipment to analyze the sample’s formation. Working with mass spectrometers, where you can apply physics and chemistry to try to understand rocks from Earth and other planets, brought together everything I wanted to do and to learn about.

Then Professor Crozaz mentioned that she was going to hunt for meteorites in Antarctica . . .

A couple of years later, in December 1992, I was on a snowmobile. Six of us had been dropped by plane on an ice field roughly 100 miles from McMurdo Base, the largest camp in Antarctica.

Also, there’s a unique conveyer belt–like mechanism that operates in Antarctica. These ice sheets move very slowly from the interior of the continent out toward the shoreline. They’ve been around for hundreds of thousands of years. During that time, meteorites have fallen on them, become embedded, and gotten carried along. The deep freeze within the ice sheets keeps the meteorites virtually pristine. Sometimes a moving ice sheet gets blocked by a mountain where high velocity winds ablate the surface, eventually exposing the meteorites. As soon as they come up, these meteorites do begin to get weathered and oxidized, but it’s much less severe than the weathering that occurs in meteorites found in hotter or wetter environments. So, in many cases, Antarctic meteorites are the better samples to study.

You might find hundreds of meteorites in a zone the size of a football field. What you do is map out the field, then space the members of your team 20 feet apart and systematically drive your snowmobiles up and down the field. When you find the first one, you holler, everybody speeds over, and you jump up and down. Then you find 10 others, and you get sort of used to it.

I was in Antarctica for more than two months of that continent’s summer. Your sense of time gets warped when there’s constant light: The days just slip by. But then the wind would start gusting, and it’d get down to –70 with the windchill, and we’d have to stay in our double-walled tents. Try that for 10 straight days and you’ll know time at the other extreme. My best advice for when time becomes interminable is: read.

Every two or three weeks we’d get a mail drop. I’d open a letter from India and think about boundaries. You know, Indian families can be pretty governing. Parents often make important life decisions for their children regarding career and marriage. I was very lucky that my family supported my decisions. Because they did, I was able to stand in places where only a handful of people have ever been. My boundaries were evolving—they still are. If there’s one thing you learn as a scientist, it’s never close your mind off to things that seem far-fetched.

I went to grad school in St. Louis, so I know about Mark McGwire. I work at the Field Museum in Chicago, so I know about Sammy Sosa. I’ve seen how the crowd reacts after home runs, especially record-breaking runs. I would never dive over anyone’s back to try to grab a home-run ball. But in the spring of 2003, I got an idea of what the scramble must feel like.

Around midnight on March 26, a meteorite shower pelted houses and streets in Park Forest, a suburb south of Chicago. This was the most densely populated urban area ever hit by a meteorite shower. People reported objects falling through their roofs, and police took a lot of the meteorites as evidence. I headed over to the police station as soon as I heard. They had 15 or 20 pieces all laid out on a table like suspects in a lineup: a rogues’ gallery of meteorites! Freshest stuff I’ve ever seen. To see and hold a meteorite that has been in space only a few hours ago is amazing. And these were chondrites, a class of meteorites that were formed early in the history of our solar system.

I started out thinking that $1 a gram would be a reasonable price to offer. But dealers and collectors descended upon Park Forest, and it became a feeding frenzy. Meteorites that break through windows and roofs are actually worth more on the dealer-collector market. There’s nothing more scientifically interesting about the house smashers than any other pieces of meteorite, but their value rises when there’s a good story attached. If they crash through your roof, you may have hit the jackpot.

People were trying to sell them for $5 to $25 a gram, so many of the pieces that weighed hundreds of grams were worth a considerable amount. There were times when I felt totally helpless. I tried to explain how much the rocks meant to science, to the museum, to me, but it’s hard for someone to be civic-minded when a lot of money is involved. People received offers that were incredibly high. What’s more, there was no assigned value. It could change the next day. So it was wild. You’d get a call from someone who’d say: “Don’t deal with my sister! She stole the meteorite from me.”

I was nervous that the Field was not going to end up with any of the meteorites. When you’re in a situation like that you can’t say to yourself, “I’m a scientist who is above this sort of stuff.” There is no high road. If you want samples, you’ve got to dive in.

We eventually got about three kilograms.

We’ve built a lab at the museum that is able to get at these questions by measuring very, very small quantities of material. It’s pretty unusual for a museum to have a laboratory of this sort.

Now there are mass spectrometers, and there are mass spectrometers. Ours arrived in a several-ton FedEx package on a pallet that was 10 feet by 10 feet. I call it the Beast—not just because of the size, but because it takes some taming to get good results. It’s very versatile in terms of the different elements it can analyze, from elements as light as lithium all the way up to uranium. We measure not just meteorites but all kinds of rock samples. The front end has a plasma torch that gets up to many thousands of degrees Celsius, as hot as the sun’s surface. It strips electrons off the atoms to make ions. Then we pull the ionized sample into the mass spectrometer, where we can measure elements that may be present in one part in a billion—or less.

We can separate these elements from the rock matrix and look at their exact chemical makeup, their isotope ratios. We can measure radioactive elements so precisely that we can determine how old a particular rock sample is. Examining the nonradioactive elements, we can look at how heavy isotopes or light isotopes are favored and learn something about the process by which they formed. So our lab focuses on timescales and processes.

We also hope to analyze samples that will be returned from future spacecraft missions to other planets and asteroids. Right now there’s actually a NASA spacecraft, Genesis, sitting between the sun and Earth collecting solar wind, that will deliver a sample to us in September. Basically, it will tell us the exact composition of the outer skin of the sun. Did you know that the sun makes up more than 99.8 percent of the mass of our solar system? That’s another one of those mind-boggling facts. Earth is really nothing in comparison. Trying to wrap your mind around the scale of objects in the universe is a constant challenge.

Sometimes it amazes me that I get to try to answer huge questions about our solar system with sophisticated, expensive laboratory equipment. I can remember a time when I couldn’t afford a simple camera to photograph the Himalayas.

The very first solid grains formed within the solar system have been very precisely aged at 4,567 million years. I think of it as coincidence that I met the guy who became my husband at a specific moment in that time span.

It happened when I was traveling back to St. Louis from Antarctica in 1993. On a whim, I decided to stop off in Hawaii to thaw out for a while. There was a professor at the University of Hawaii I thought I might want to work with as a postdoc. Mark was a graduate student there at the time—and that’s how we met.

He’s a planetary geologist. As a research professor at Northwestern University, he attends some of the same conferences I go to, but those conferences sometimes host thousands of people. There’s no knowing whether we ever would have crossed paths had I not stopped in Hawaii.

If a third person were to hear our dinner conversations, it would probably be amusing. Or not amusing at all. He might ask, “What’s the range of iron content in the ordinary chondrites?” After dinner, it’s “Oh, I downloaded this really neat set of Mars Global Surveyor images. Wanna take a look?”

When you think of what happened to the space shuttle Columbia last year, it’s hard to get past the enormity of the blow to the families of the astronauts and the rest of us. For me, there was more involved. I’d known one of the astronauts, Kalpana Chawla, since I was 11. Her family lived in Karnal, a small town between Delhi and Chandigarh. She was about five years older than me and attended aeronautical engineering school. That was an unusual choice for a woman. She was interested in learning to fly. I remember being a little in awe of her.

The last time I saw her was in India in the early ’80s. I had the opportunity to catch up with her because I go to Houston every year for a planetary science conference. Many times I thought about getting in touch with her. But you get so busy, and I never did. It’s sad. There I was trying to wrap my mind around concepts like the depth of geologic time, and I didn’t take the 5 or 10 minutes to call her and see how she was doing.

The last year or so I’ve wondered about having kids. there’s work  in the lab—teaching, communicating with the public at the museum. It’s a challenge. I know women who always knew they wanted children. And I also know women who have not had them and have no regrets. I don’t have any desire right now. But when I see other women with children, I wonder, “Am I missing out on something important?” One thing everybody tells me: There’s no perfect time to have children. I’m 36. The unfortunate part is I don’t have too much time to figure it out.

I would love to have, within my lifetime, actual rocks picked up from the surface of Mars to examine in my laboratory. There’s a chance that the meteorites I’ve looked at from Mars are samples of atypical rocks on that planet. At the moment, there are no plans to bring back samples. The cost of such a mission is likely to be high—certainly higher than NASA’s Discovery class missions and also the New Frontiers missions that are planned. But I remain the eternal optimist.

There are questions that we’ll never have the answers to in our lifetime. But we can keep trying and lay down steps for those with that same sense of wonder who come after us.

The simple act of gazing at the stars allows us to see the universe back in time. I remember staring up at the sky with amazement the night after I’d learned that. I must have been 13. It’s hard to believe that there is now an asteroid named after that girl.

Astronomers have the prerogative of naming asteroids they discover. They nominate people based on research and accomplishments, and the nominations must be approved by the International Astronomical Union.

Carolyn Shoemaker and her husband, Gene, discovered this asteroid. The largest known asteroid is about 600 miles across, but many are much smaller. This particular one is not very big—a few tens of miles perhaps. In 1999 it was named Wadhwa. I’ve never seen it, and it’s unlikely that I ever will. But the great part is that it’s a Mars-crossing asteroid. So you never know, one day I just might have an impact on Mars.