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Fluid ‘time capsules’ in salt shake up traditional views on seawater chemistry

Tim Lowenstein, a professor of geology who specializes in low-temperature geochemistry, is proving that the salt of the earth is peppered with important clues about the planet’s prehistoric past.

His research has as many facets as the salt crystals he studies. It is helping to reclaim from lake sediments ancient data that could help us to better understand the indicators of worldwide climate change. It is providing new contexts for the history and evolution of ocean-dwelling plants and animals. And, as documented in an article in the November 2, 2001 issue of Science, it is debunking age-old presumptions that the chemistry of seawater has remained unchanged for the past 600 million years.

“The relative amounts of salts in today’s oceans are the same everywhere,” Lowenstein said. “What we’re saying is that the levels of specific salts have fluctuated over very long time frames of 100 to 200 million years, and that the fluctuations we’re documenting seem to correspond quite nicely with the fossil record indicating that certain organisms have risen and fallen with the change in seawater chemistry.”

Coral, the animal that comprises today’s coral reefs, for instance, builds its skeleton out of a type of calcium carbonate called aragonite, Lowenstein said.

“At other times, reefs were made up of other animals, not coral, and those animals built their skeletons out of calcite.”

These changes correspond with the oscillations in seawater chemistry that Lowenstein and his research group have recorded.

Another application of Lowenstein’s work conceivably could help to shed new light on the origins of life on this planet. Techniques developed by his research team have been key in his collaboration with colleagues at West Chester University in Pennsylvania. There researchers are working to unravel the mysteries surrounding a Methuselan bacterium that was revived in the year 2000 after surviving 250 million years entombed in salt crystals.  The bacterium, dubbed 2-9-3, is a contender for the title of “the world’s oldest known organism,” and seems to push back by hundreds of millions of years the timeline of life. More than that, it seems to open up the possibility that life, in the form of bacteria, could originally have been transported to Earth by meteorites. Salt crystals similar to those containing the 2-9-3 bacterium were found in a meteorite in 1999, Lowenstein said.

Tapped for close to $525,000 in National Science Foundation awards over the past four years, Lowenstein received the University’s Excellence in Research award this year. He is an authority on the origin and significance of evaporites. These are sedimentary rocks composed of 50 or more saline minerals, the most common of which is halite, or common rock salt.  His main research focus, however, is “fluid inclusions,” small pockets of ancient seawater or other fluids that become trapped in ancient salt or rock formations. The bacterium being studied at West Chester was discovered in a fluid inclusion retrieved from a salt bed about a third of a mile beneath the earth’s surface near Carlsbad, N.M.  Lowenstein this summer gathered samples from salt mines that extend hundreds of feet beneath the city of Detroit to look for inclusions that might similarly contain signs of life.

Some fluid inclusions appear as bubbles large enough to be seen by the naked eye. Fluid inclusions in clear salt crystals were actually used, in fact, as the bubbles in early leveling tools, Lowenstein said.  Still, most fluid inclusions are only a fraction of the width of a human hair. Until recently, this made it difficult for researchers to work with them, and no matter the results, every analysis was subject to charges that ancient fluids might have been contaminated in the process.

Today, however, reliable scientific analysis of the ancient fluids is possible because of a new technique developed by Lowenstein’s research group, most notably Michael Timofeeff, Sean Brennan and microbeam specialist William Blackburn. The technique involves freezing and slicing open the inclusions and, then, using X-rays to determine their chemical composition.

Using this technique to analyze the chemistry of fluid inclusions from salt crystals gathered from Australia, the Middle East and the Americas, Lowenstein and his research group are showing that the chemistry of seawater has actually oscillated back and forth, perhaps every 200 million years or so, perhaps based on major shifts in the tectonic plates.

Some salt crystal samples Lowenstein has examined contained ancient seawater up to 500 or 600 million years old.

“These fluid inclusions are like tiny little time capsules of sea water and sometimes of life that could have been trapped in it.”

Lowenstein’s work also has major implications in the study of ancient climates. Since salts are formed by evaporation, salt itself provides “beautiful records of past climates,” by helping researchers determine if the climate was wetter or drier, hotter or colder, he said. More specific temperatures can be determined because fluid inclusions  serve as “little thermometers,” he said.  Researchers can figure out the temperatures at which salts were grown by using the homogenization temperature of fluid inclusions as a gauge, he said.

Increasing our knowledge of ancient climate changes could eventually help us to predict future climate changes, Lowenstein said, but it isn’t likely to do much to improve the accuracy of the weekend weather forecast. His work on samples taken from a dry basin in Bolivia indicates, for instance, shows that about 20,000 years ago, the area was the site of freshwater lake, probably hundreds of feet deep.

“I guess the hope for us is that we will eventually have a better understanding of long-term records of climate change so that we can look for clues about what might be driving it.”

Lowenstein isn’t yet used to seeing his research reported in places like The New York Times, which ran an article referring to his work last month.  But with journals, journalists and research scientists from around the world taking notice of his work, one thing seems certain: Lowenstein’s research will never again be taken with a grain of salt.

Related Links

Science [1]

Tim Lowenstein’s Home Page [2]

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