Commentary by Roger Martin Martin writes about research at KU for Kansas media and in a Web zine. Contact Martin at rmartin@kucr.ukans.edu or (785) 864-7239. Martin also can be heard on KANU 91.5 FM public radio Archives More articles by Roger Martin Subscribe now to receive KU News by email

Water drops hold key to Earth's history

by Roger Martin

Seawater knows how to hang around.

And hang around.

And hang around.

Our human ancestors came from the oceans, and even today, about 70 percent of the human body is mildly salty water. Without enough salt, the heart won't beat and food won't digest.

You know what else is full of salt? Rocks. Many contain seawater that became trapped in their crystals hundreds of millions of years ago.

This fossil water is telling scientists about the Earth's history.

A little more than a year ago now, a Pennsylvania researcher reported finding a 250 million-year-old bacterium. He found the germ trapped, he said, in a tiny pocket of brine. The brine was nested inside a crystal.

Some scientists didn't believe it. The germ, they contended, had slipped into the brine pocket way more recently than any 250 million years ago.

Even so, plenty of scientists are poking around inside crystals formed millions of years ago, prospecting for trapped fluids and gases.

The waters trapped inside crystals have a fancy name: fluid inclusions. Robert Goldstein, a distinguished professor of geology at the University of Kansas, has written a whole book about them. His article in the November issue of Science magazine described what fluid inclusions can tell us about the environment of the ancient Earth.

Some fluid inclusions are found in salt crystals and other minerals that were deposited as seas dried up. Others are bottled up in glacial ice and have information about prehistoric atmospheres.

The size of inclusions makes them a difficult study. They may be only a few micrometers wide -- only one-tenth the width of a human hair.

Another challenge, says Goldstein, is removing water samples from the inclusion space without tainting them. Still another is making sure that nothing within the inclusion space contaminates the fluid.

This problem arose with one of the first inclusions ever discovered. In the late 1980s, a scientist found gas bubbles trapped in amber and thought he'd found remnants of the ancient atmosphere.

Actually, he'd found remnants of the amber's breakdown.

Even with all these problems, fluid inclusions have started to yield secrets about Earth's history.

Inclusions in rocks half a billion years old are telling us, for example, that the oceans have changed and that the ancient atmosphere was much richer in carbon dioxide than today's.

What really blows me away, though, is the idea that fluid stays locked up in crystals for hundreds of millions of years.

And get this: Some of these tiny pockets of fluid contain a bubble, and that bubble is maybe one-fiftieth the width of a human hair. Subtle temperature variations around the crystal can keep that bubble dancing for a hundred million years!

It also boggles me to think that humans, like the crystals of a great many rocks we pick up, are full of the sea. Our blood is about 1 percent salt, sea water about 3.5 percent salt.

Rocks and people: Trace us back far enough, and you'll see that we both come from a cradle of brine.