Featured Research

from universities, journals, and other organizations

Scientists refine Earth's clock: Some events in planet's history happened more recently than previously thought

Date:
March 29, 2012
Source:
British Geological Survey
Summary:
New research has revealed that some events in Earth's history happened more recently than previously thought. Scientists have refined the data used to determine how much time has passed since a mineral or rock was formed. They report uranium isotopic composition of minerals, used to date major geological events, which are more accurate than previously published.

238U/235U is measured with a mass spectrometer.
Credit: Image courtesy of British Geological Survey

New research has revealed that some events in Earth's history happened more recently than previously thought. Scientists from the British Geological Survey and the Massachusetts Institute of Technology, publishing recently in the journal Science, have refined the data used to determine how much time has passed since a mineral or rock was formed. They report uranium isotopic composition of minerals, used to date major geological events, which are more accurate than previously published. The major effect of this is to reduce previous age determinations by up to 700,000 years.

Minerals naturally capture uranium when they form, which in turn undergoes a chain of radioactive decays to other elements, ending with lead. This new research has shown that, by more accurately measuring the relative amount of the uranium isotopes 238U and 235U, we now have a better understanding of how much time has passed since a mineral or rock has formed.

A major effect of this work will be to decrease all previous uranium-lead (U-Pb) age determinations, by up to 700,000 years for samples that are about 4.5 billion years old -- the age of Earth. In particular, the new 238U/235U ratio will allow geologists to place more accurate limits on the exact timing of a broad range of geological processes, from the initial formation of our planet, continents and economic mineral deposits, to past evolutionary events and climate change. Left: Uranium is purified from dissolved minerals. Right: 238U/235U is measured with a mass spectrometer.

Blair Schoene, a geologist from Princeton University said "This new determination will not only improve the accuracy of each U-Pb age but ultimately our understanding of events in Earth history."

For over 35 years, a 238U/235U ratio of 137.88 has been used to calculate U-Pb dates, from the oldest rocks that formed four billion years ago, to much younger rocks that are hundreds of thousands of years old. When scientists recently evaluated the measurements used to arrive at the 137.88 value, they came to a dead end: the value could not be traced back to standard units such as the kilogram.

This new study shows that many naturally occurring uranium-rich minerals, such as zircon, actually have a lower 238U/235U value with an average of 137.818 0.045 (the uncertainty assigned to this value relates to the variation observed between different samples).

Agreement between these results, other rocks, and meteorites indicate the new average 238U/235U value and uncertainty may also be representative of Earth's 'bulk' uranium isotopic composition.


Story Source:

The above story is based on materials provided by British Geological Survey. Note: Materials may be edited for content and length.


Journal Reference:

  1. J. Hiess, D. J. Condon, N. McLean, S. R. Noble. 238U/235U Systematics in Terrestrial Uranium-Bearing Minerals. Science, 2012; 335 (6076): 1610 DOI: 10.1126/science.1215507

Cite This Page:

British Geological Survey. "Scientists refine Earth's clock: Some events in planet's history happened more recently than previously thought." ScienceDaily. ScienceDaily, 29 March 2012. <www.sciencedaily.com/releases/2012/03/120329141918.htm>.
British Geological Survey. (2012, March 29). Scientists refine Earth's clock: Some events in planet's history happened more recently than previously thought. ScienceDaily. Retrieved July 31, 2014 from www.sciencedaily.com/releases/2012/03/120329141918.htm
British Geological Survey. "Scientists refine Earth's clock: Some events in planet's history happened more recently than previously thought." ScienceDaily. www.sciencedaily.com/releases/2012/03/120329141918.htm (accessed July 31, 2014).

Share This




More Earth & Climate News

Thursday, July 31, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

Visitors Feel Part of the Pack at Wolf Preserve

Visitors Feel Part of the Pack at Wolf Preserve

AP (July 31, 2014) Seacrest Wolf Preserve on the northern Florida panhandle allows more than 10,000 visitors each year to get up close and personal with Arctic and British Columbian Wolves. (July 31) Video provided by AP
Powered by NewsLook.com
Florida Panther Rebound Upsets Ranchers

Florida Panther Rebound Upsets Ranchers

AP (July 31, 2014) With Florida's panther population rebounding, some ranchers complain the protected predators are once again killing their calves. (July 31) Video provided by AP
Powered by NewsLook.com
Big Waves In Arctic Ocean Threaten Polar Ice

Big Waves In Arctic Ocean Threaten Polar Ice

Newsy (July 30, 2014) Big waves in parts of the Arctic Ocean are unprecedented, mainly because they used to be covered in ice. Video provided by Newsy
Powered by NewsLook.com
Raw: Thousands Flocking to German Crop Circle

Raw: Thousands Flocking to German Crop Circle

AP (July 30, 2014) Thousands of people are trekking to a Bavarian farmer's field to check out a mysterious set of crop circles. (July 30) Video provided by AP
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:

Breaking News:
from the past week

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



    Save/Print:
    Share:

    Free Subscriptions


    Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

    Get Social & Mobile


    Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

    Have Feedback?


    Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
    Mobile: iPhone Android Web
    Follow: Facebook Twitter Google+
    Subscribe: RSS Feeds Email Newsletters
    Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins