SOLAR SYSTEM

The Extreme Files

by Diane Boudreau

A few brave souls enjoy living life to the extreme. Some people climb mountains so tall they need oxygen tanks to breathe. Others explore the freezing reaches of Antarctica. A few fly airplanes faster than the speed of sound.

However, people aren't the only ones who take life to the extreme. Jack Farmer is a planetary geologist at Arizona State University. He works with daredevils of a tinier sort-microbes. Some of these microscopic creatures live in almost impossible places. They float around in hot springs with scalding water temperatures as high as 237 degrees Fahrenheit. Or they live in lakes filled with chemicals that would burn human skin.

"These are extreme environments where higher life forms are excluded," Farmer says. "The types of organisms that live here are called 'extremophiles.'"

Extremophiles live in places where most animals and plants can't survive. Their homes include some of the hottest, coldest, saltiest, most acidic, or most alkaline places in the world.

Besides being just plain fascinating, extremophiles can teach us about the beginnings of life on Earth, and possibly on other planets.

"We believe the early Earth was a microbial world," Farmer says. In fact, the common ancestor of all modern living things was probably a type of extremophile called a hyperthermophile. Hyperthermophiles live at temperatures above 176 degrees Fahrenheit (80 degrees Celsius).

"Hyperthermophiles are very deeply rooted in the universal tree of life," says Farmer.

Scientists think they have found evidence of life on Earth as long ago as 3.9 billion years. But some time between 4.4 and 3.8 billion years ago, when life was just beginning, scientists think that several huge meteorites slammed into Earth.

When they hit, these objects vaporized the oceans and raised the surface temperature on Earth. As the climate heated up, only the hyperthermophiles survived. Everything else died, leaving just the heat-loving creatures to repopulate the Earth.

By studying these kinds of microbes, Farmer can learn about the early Earth. He studies the extremophiles that live today, and the fossils they leave behind.

Most fossils consist of bones, teeth, or shells-hard parts that don't decay over time. Microbes are completely soft-bodied, so they hardly ever form fossils. But under certain special conditions, they can be preserved.

Farmer finds lots of microbial fossils at Mono Lake in California. Mono Lake is a very unusual lake. First, it is almost three times saltier than seawater. The lake also has a pH level of 10.5, which is highly alkaline. Pure water only has a pH of 7. Mono Lake is closer to bleach, which has a pH of just below 13.

"You get a mild chemical burn when you dive into the lake, which I've done," says Farmer. "Your skin flakes off for days afterward."

Not many kinds of creatures can live in this kind of environment, but some do. Most of the inhabitants of Mono Lake are diatoms (a type of algae) and other microscopic life forms such as brine shrimp and the larvae of alkali flies.

"That's pretty much it," says Farmer. Mono Lake is a very important environment, however, because it is a kind of service station for migrating birds, who stop there to eat these little creatures.

The microbes are what interest Farmer the most. He studies how they leave behind a record of themselves.

The microbes at the bottom of Mono Lake clump together in communities. Many flourish around springs on the lake floor, where calcium carbonate (lime) and other minerals crystallize from the water. As the minerals form, they surround the microbes and form bigger structures that you can see without a microscope. Scientists often find fossil microbes inside these structures. Some of them form clumps of filaments that look like a tiny head of hair.

Over time, the microbes themselves usually decay, but the structures around them preserve their shape, size, and orientation.

Imagine pressing a leaf into clay, then letting the clay dry. If you peeled off the leaf, you would find a permanent impression in the clay. If you showed your "fossil" to another person, he or she might be able to identify what kind of leaf you used based on its shape and size. In the same way, Farmer tries to identify microbes based on their fossils.

Sometimes, when the rock forms quickly enough, microbes get trapped inside before they can decay.

"It's like being vacuum-packed in," explains Farmer. "The material is preserved, potentially forever, until the rock is broken apart. If it gets entombed fast enough it can't decay. There are fossil microbes preserved like this that are older than 3 billion years."

Farmer studies the information stored in these fossils, and the storage process itself. To do this, he examines every stage of the process. He studies the microbes while they're living and when they start to become fossilized. The ASU scientist also studies how the surrounding rock changes as the fossil is buried.

This approach helps him recognize ancient fossils that were alive long before people walked on our planet. Farmer is learning about Earth's earliest history. He also is gathering information that will help us look for life on other planets.

"We don't think that Mars is a good place for life today, but it could have been in the past," he says. "When we look at the early geologic record on Earth, it is like going to another planet, things were so different back then. Why not look for life on other planets in the same way we would look for early life on Earth?" Farmer asks.

Looking for microbial fossils on Mars is hard to do from more than 35 million miles away. One way to search is by using an infrared spectrometer, like ASU's TES device (see Invisible Mars). Farmer and other researchers are using such a device at Mono Lake to answer questions about how to search for life signs during future Mars missions.

Scientists have lots of questions. Can we detect these kinds of deposits from orbit? What kind of distance and resolution are required?

Farmer also studies hyperthermophiles, the microbes that thrive in extremely hot water. Some microbes can grow at temperatures up to 237 degrees F (114 degrees C), and survive at temperatures as high as 266 degrees F (130 degrees C). That's hotter than boiling water!

Scientists have discovered organisms that live in hot springs and near heated vents on the ocean floor. Farmer does lots of work at Yellowstone National Park, a giant volcanic area dotted with hundreds of such hot springs.

"You'd think these places would be sterile, but they're not," says Farmer. "We think we're sterilizing things by running them through the dishwasher, but many microbes can live under really harsh conditions. Fortunately, most of these microbes are harmless to us, and some even help us. For example, we have microbes that live in our digestive systems that help us digest our food."

Stomach acid, boiling water, salty lakes-none of these things get in the way of the drive to survive.

"Near the bubbling hot springs at Yellowstone, we are hard-pressed to find a rock without evidence of life on it," says Farmer.

Lots of volcanoes rise from the surface of Mars. Scientists now know that many of these volcanoes exist in spots where water flowed long ago, or where ice was present. Farmer thinks that microbes could have lived near these hot spots, just like they do on Earth today. His research will help us find out for sure.