Hot springs microbes hold key to dating sedimentary rocks, researchers say

Mammoth Hotsprings in Yellowstone National Park
Mammoth Hotsprings in Yellowstone National Park

Scientists studying microbial communities and the growth of sedimentary rock at Mammoth Hot Springs in Yellowstone National Park have made a surprising discovery about the geological record of life and the environment.

Their discovery could affect how certain sequences of sedimentary rock are dated, and how scientists might search for evidence of life on other planets.

“We found microbes change the rate at which calcium carbonate precipitates, and that rate controls the chemistry and shape of calcium carbonate crystals,” said Bruce Fouke, a professor of geology and of molecular and cellular biology at the University of Illinois.

In fact, the precipitation rate can more than double when microbes are present, Fouke and his colleagues report in a paper accepted for publication in the Geological Society of America Bulletin.

The researchers’ findings imply changes in calcium carbonate mineralization rates in the rock record may have resulted from changes in local microbial biomass concentrations throughout geologic history.

A form of sedimentary rock, calcium carbonate is the most abundant mineral precipitated on the surface of Earth, and a great recorder of life.

“As calcium carbonate is deposited, it leaves a chemical fingerprint of the animals and environment, the plants and bacteria that were there,” said Fouke, who also is affiliated with the university’s Institute for Genomic Biology.

The extent to which microorganisms influence calcium carbonate precipitation has been one of the most controversial issues in the field of carbonate sedimentology and geochemistry. Separating biologically precipitated calcium carbonate from non-biologically precipitated calcium carbonate is difficult.

Fouke’s research team has spent 10 years quantifying the physical, chemical and biological aspects of the hot springs environment. The last step in deciphering the calcium carbonate record was performing an elaborate field experiment, which drew water from a hot springs vent and compared deposition rates with and without microbes being present.

“Angel Terrace at Mammoth Hot Springs in Yellowstone National Park is an ideal, natural laboratory because of the high precipitation rates and the abundance of microbes,” Fouke said. “Calcium carbonate grows so fast – millimeters per day – we can examine the interaction between microorganisms and the calcium-carbonate precipitation process.”

The researchers found that the rate of precipitation drops drastically – sometimes by more than half – when microbes are not present.

“So one of the fingerprints of calcium carbonate deposition that will tell us for sure if there were microbes present at the time it formed is the rate at which it formed,” Fouke said. “And, within the environmental and ecological context of the rock being studied, we can now use chemistry to fingerprint the precipitation rate.”

In a second paper, to appear in the Journal of Sedimentary Research, Fouke and colleagues show how the calcium carbonate record in a spring’s primary flow path can be used to reconstruct the pH, temperature and flux of ancient hot springs environments. The researchers also show how patterns in calcium carbonate crystallization can be used to differentiate signatures of life from those caused by environmental change.

“This means we can go into the rock record, on Earth or other planets, and determine if calcium carbonate deposits were associated with microbial life,” Fouke said.

Why Is The Ocean Salty?

Pacific Ocean at dawn. Today's ocean salt has ancient origins. As the earth formed, gases spewing from its interior released salt ions that reached the ocean via rainfall or land runoff. (Credit: Michele Hogan)
Pacific Ocean at dawn. Today’s ocean salt has ancient origins. As the earth formed, gases spewing from its interior released salt ions that reached the ocean via rainfall or land runoff. (Credit: Michele Hogan)

The saltiness of the sea comes from dissolved minerals, especially sodium, chlorine, sulfur, calcium, magnesium, and potassium, says Galen McKinley, a UW-Madison professor of atmospheric and oceanic sciences.

Today’s ocean salt has ancient origins. As the earth formed, gases spewing from its interior released salt ions that reached the ocean via rainfall or land runoff.

Now, the ocean’s salinity is basically constant. “Ions aren’t being removed or supplied in an appreciable amount,” McKinley says. “The removal and sources that do exist are so small and the reservoir is so large that those ions just stay in the water.” For example, she says, “Each year, runoff from the land adds only 0.00005 percent of total ocean salts.”

In lakes, relatively rapid turnover of water and its dissolved salts keeps the water fresh – a water droplet and its ions will stay in Lake Superior for about 200 years, compared to roughly 100 to 200 million years in the ocean. “Even if you did have any accumulation of an ion in a lake, it would be washed out quickly,” McKinley explains.

Ocean salts, however, have no place to go. “The ions that were put there long ago have managed to stick around,” McKinley says. “There is geologic evidence that the saltiness of the water has been the way that it is for at least a billion years.”

Geologist Discovers Three New Minerals

On a geological expedition along the windswept slopes of the Larsemann Hills in Antarctica, UMaine geologist Edward Grew collected samples of the area’s unique rock formations that would later reveal three minerals previously unknown to science. The minerals, stornesite-(Y), chopinite and tassieite, are extremely rare and represented only by microscopic samples collected by Grew.

The unique mineralogy of the Larsemann Hills, located on the eastern shore of Prydz Bay in Princess Elizabeth Land, inspired Grew and his fellow researcher Chris Carson (now at Geoscience Australia) to make the four-month expedition in 2003 – 2004, which was funded by the National Science Foundation and made possible by the Australian Antarctic Division.

Grew and his colleagues identified and characterized the minerals using cutting edge technologies. Martin Yates used the powerful electron microprobe at UMaine to image the new minerals and measure their chemical compositions. Next, the minerals were sent to Olaf Medenbach at the Ruhr University (Bochum, Germany) and Thomas Armbruster at the University of Bern (Switzerland), who determined the new minerals’ optical properties and crystal structures, respectively. Then Grew submitted a complete dataset for each mineral to a special commission of the International Mineralogical Association, which formally approved them as valid new species. Grew has discovered a total of ten new minerals, and sees each as an opportunity to expand scientific understanding of the Earth and its complex geological processes.

“When new minerals are identified, some have little significance, and some end up being tremendously important,” said Grew. “They all tell us something about how rocks form. Ultimately, discoveries like these contribute to our understanding of the origin of rocks, plate tectonics and other processes, and give us valuable insights into temperature, pressure and other conditions within the Earth at different points of its history.”

Geologist discovers Martian mineral

Geology professor Ron Peterson discovered natural crystals in a frozen BC pond similar to ones that he grew in his garage -- and are also believed to exist on Mars. - Photo Courtesy: Ron Peterson
Geology professor Ron Peterson discovered natural crystals in a frozen BC pond similar to ones that he grew in his garage — and are also believed to exist on Mars. – Photo Courtesy: Ron Peterson

A Queen’s University researcher’s surprising discovery – made first in his garage and later verified through field work – has resulted in the naming of a new mineral species that may exist on Mars, and has caught the attention of the NASA space program.

Geologist Ron Peterson’s findings will be reported in the October issue of the journal, American Mineralogist. Dr. Peterson, who was invited to Houston last fall to present his original findings at the Johnson Space Center, continues to work with NASA scientists on Mars research.

The new mineral, meridianiite, is unusual because it is a planetary mineral and also thought to exist on the moons of Jupiter.

Also on the research team are Bruce Madu from the B.C. Ministry of Energy, Mines, and Petroleum Resources, Queen’s Chemistry Professor Herb Shurvell, and high school student Will Nelson, from Ascroft, B.C.

The Queen’s discovery was inspired by information sent back from Mars by the Mars Exploration Rover (MER), Opportunity, indicating that magnesium sulfate is present on that planet’s surface. The rover also sent back photographs of voids in rocks that are thought to have originally contained crystals.

This supports the team’s theory that regions of Mars were once covered with water, which later froze and then evaporated, leaving a residue of crystal molds in the sediment.

Based on these observations, in the winter of 2005, Dr. Peterson left a solution of drugstore epsom salts (hydrated magnesium sulfate) to crystallize in his unheated garage for several days. He then rushed the frozen crystals to a Queen’s chemistry lab, where experiments showed them to be an unusual form of magnesium sulfate that displayed some of the same properties reported earlier by Mars rovers.

Dr. Peterson wondered whether the same mineral might be found on Earth. In the fall of 2006 he located some ponds near Ashcroft in the Okanagan Valley of B.C., from which magnesium sulfate had once been mined. He then enlisted the help of a local high-school chemistry student to send him mineral samples from the ponds, by mail, throughout the fall.

In February 2007 Dr. Peterson visited the frozen ponds himself, and brought back crystals in a cooler packed with dry ice. These natural crystals were put through a series of tests, and in June meridianiite was approved as a new valid mineral species by the Commission on New Mineral names and Mineral Nomenclature of the International Mineralogical Association.

-The name was chosen to reflect the locality on Mars where a rover had observed crystal molds in sedimentary rock that are thought to be caused by minerals that have since dehydrated or dissolved,- says Dr. Peterson. -Observations obtained by using the rover wheels to dig trenches into the Martian soil show that magnesium sulfate minerals have been deposited below the surface.-

Between 20 and 30 new minerals are identified each year, the researcher notes, but -these often involve rare elements.- Meridianiite, on the other hand, is formed from the common materials magnesium, sulfate and water.

A geologist who normally studies mine waste, Dr. Peterson admits he has been a -space geek- since childhood, and says that working on this project has been exciting. -It began with a moment of insight – based on my previous geological experience – and now I have the chance to collaborate with experts from around the world who are studying the geology of the Martian surface.-