Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Geologists make better estimates of rock ages, study global climate change

25.10.2006
Ohio State University geologists have found that important rocks from Niagara Gorge -- rock formations that are used to judge the ages of rocks and fossils around North America -- formed five times faster than previously thought.

The finding means that scientists will have to re-examine studies of sedimentary rock deposited across North America during the Silurian period, from 416 to 443 million years ago.

Ultimately, the geologists hope to perform similar studies of rock from other time periods, to better pinpoint periods of global climate change in Earth's history. Just as tree rings, coral reefs, and ice cores contain chemical records of Earth's history, sedimentary rocks such as limestone vary in composition according to the climate in which they formed.

Bradley Cramer, a doctoral student in earth sciences at Ohio State , reported the study October 22 at the Geological Society of America meeting in Philadelphia.

Cramer and his advisor, Matthew Saltzman, professor of earth sciences, and their colleagues used a relatively new technique called high-resolution carbon isotope stratigraphy to determine the age of rocks in Niagara Gorge in New York .

Rocks that were originally estimated to have formed as sediments built up over 10 million years' time actually formed in only 2 million years, they found. That means that instead of forming between 428 and 418 million years ago, the rocks actually formed between 428 and 426 million years ago.

What do a few million years matter, when they happened so long ago? Saltzman and his team need to make precise time measurements as they search for evidence of ancient climate change.

"We have this great geological record of climate changes in the past," Cramer said. "The problem is, the rate of change that we're worried about in the modern day is on a very short time scale. And when we look into the deep past, our ability to know where we are in time isn't that precise. If we can get our time constraints down more precisely, we can begin to ask the same sort of questions of the past that we're asking of the modern era."

Ancient sedimentary rocks contain chemicals such as carbon that are indicators of atmospheric conditions at the time the rocks formed. During times of apparent rapid climate change at other locations around the globe, the rock composition shows a change as well, and pinpointing exactly when things happened can be difficult.

That's why the Ohio State geologists decided to re-examine the rock formations of Niagara Gorge, which had originally been studied in the 1800s.

"That very set of rocks contains a global extinction event -- one of the largest in Earth's history," Saltzman said, "and it hadn't been examined with the most modern techniques available."

Scientists believe this extinction event, the Ireviken event, happened approximately 428 million years ago, and may have been caused by climate change. Some 80 percent of conodont species -- wormlike sea creatures -- and 50 percent of trilobite species went extinct during that time.

The event was recorded in the rock composition of Niagara Gorge, and carbon isotope stratigraphy is the ideal technique to study it.

Cramer explained how the technique works. Scientists measure the ratio between two isotopes of carbon, carbon-13 and carbon-12, in a rock sample. Normally, the ratio is zero or one, but in certain times throughout history, such as during and after a great extinction, the ratio markedly increases. Scientists call the increase an "excursion" from the normal value of zero or one.

"What is so useful about these excursions is that they are time markers," Cramer said. "If you find an excursion in Ohio , and then the same one in Sweden , you know that the intervals containing the excursion are coincident in time. Essentially, we match the markers from one place to another. This is a chemical way of telling time."

The Niagara Gorge rocks contained a marker from the Ireviken extinction. That marker had been well documented in rocks in sites around the United States, Canada, and Sweden. In all those locations, the rocks that contain the marker formed at the same time in Earth's history.

The Niagara Gorge rocks were among the first North American rocks to be dated by geologists in the 1800s, and the gorge has been a treasure trove for scientists ever since. From the top of the escarpment, down to the floor of the gorge where the Niagara River cascades, scientists have thought that the gorge represented as much as 10 million years of history.

Cramer's analysis revealed that most of the formations originated during the Ireviken event, which lasted for only 1 million years or so.

Given this new information, the geologists decided that the formations of Niagara Gorge only represent 2 million years of history. Rock formations there are used as a frame of reference to judge the ages of rocks throughout North America . So these new results mean that many scientists will have to revise their work. Estimates of when certain animals went extinct may change.

"Unfortunately, this means that a lot of people are going to have to re-examine work that they thought was done," Cramer said.

Next, he wants to look further back in time, to the period before the Silurian: the Ordovician, which began 488 million years ago. Geologists disagree on where exactly the boundary between the Ordovician and the Silurian should be placed, and carbon isotope stratigraphy is an ideal tool to help solve the problem.

Ohio State coauthors on the presentation included Mark Kleffner, an associate professor, Stig Bergström, a professor emeritus, and Seth Young, a doctoral student, all of earth sciences.

The Friends of Orton Hall Fund -- a fund provided by Ohio State earth sciences alumni -- and the Geological Society of America funded this work. A laboratory at the University of Erlangen-Nuremberg in Germany analyzed the Niagara Gorge rock samples.

Matthew Saltzman | EurekAlert!
Further information:
http://www.osu.edu

More articles from Earth Sciences:

nachricht NASA looks to solar eclipse to help understand Earth's energy system
21.07.2017 | NASA/Goddard Space Flight Center

nachricht Scientists shed light on carbon's descent into the deep Earth
19.07.2017 | European Synchrotron Radiation Facility

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Manipulating Electron Spins Without Loss of Information

Physicists have developed a new technique that uses electrical voltages to control the electron spin on a chip. The newly-developed method provides protection from spin decay, meaning that the contained information can be maintained and transmitted over comparatively large distances, as has been demonstrated by a team from the University of Basel’s Department of Physics and the Swiss Nanoscience Institute. The results have been published in Physical Review X.

For several years, researchers have been trying to use the spin of an electron to store and transmit information. The spin of each electron is always coupled...

Im Focus: The proton precisely weighted

What is the mass of a proton? Scientists from Germany and Japan successfully did an important step towards the most exact knowledge of this fundamental constant. By means of precision measurements on a single proton, they could improve the precision by a factor of three and also correct the existing value.

To determine the mass of a single proton still more accurate – a group of physicists led by Klaus Blaum and Sven Sturm of the Max Planck Institute for Nuclear...

Im Focus: On the way to a biological alternative

A bacterial enzyme enables reactions that open up alternatives to key industrial chemical processes

The research team of Prof. Dr. Oliver Einsle at the University of Freiburg's Institute of Biochemistry has long been exploring the functioning of nitrogenase....

Im Focus: The 1 trillion tonne iceberg

Larsen C Ice Shelf rift finally breaks through

A one trillion tonne iceberg - one of the biggest ever recorded -- has calved away from the Larsen C Ice Shelf in Antarctica, after a rift in the ice,...

Im Focus: Laser-cooled ions contribute to better understanding of friction

Physics supports biology: Researchers from PTB have developed a model system to investigate friction phenomena with atomic precision

Friction: what you want from car brakes, otherwise rather a nuisance. In any case, it is useful to know as precisely as possible how friction phenomena arise –...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Closing the Sustainability Circle: Protection of Food with Biobased Materials

21.07.2017 | Event News

»We are bringing Additive Manufacturing to SMEs«

19.07.2017 | Event News

The technology with a feel for feelings

12.07.2017 | Event News

 
Latest News

NASA looks to solar eclipse to help understand Earth's energy system

21.07.2017 | Earth Sciences

Stanford researchers develop a new type of soft, growing robot

21.07.2017 | Power and Electrical Engineering

Vortex photons from electrons in circular motion

21.07.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>