Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Extreme melting event defines Earth’s early history

17.06.2005


Could Earth have had an even more violent infancy than previously imagined? New isotope data suggest that the Earth not only had a very violent beginning but also point to new information about our planet’s chemical evolution.



New and precise measurements of a neodymium isotope ratio (142Nd/144Nd) led Maud Boyet and Rick Carlson of Carnegie Institution’s Department of Terrestrial Magnetism to the discovery that all terrestrial rocks have an excess of 142Nd compared to the expected building blocks of the planet. The results will appear in the June 16, 2005 edition of Science.

Prior research suggested that the Earth formed by the accumulation of planetesimals -- small cold bodies present in early solar system history. The chemical composition of these early bodies is reflected today in a type of stony meteorite called chondrites. Scientists had expected that the Earth would have a composition similar to these meteorites. However, this new research challenges these earlier conclusions by showing that terrestrial rocks have excess 142Nd caused by the radioactive decay of the now extinct isotope 146Sm.


One possible explanation of the difference in 142Nd/144Nd between Earth and chondrites is that the Earth’s average composition is not chondritic, but on the basis of several chemical arguments this explanation is unlikely. More probable is that the portion of the Earth involved in creating crustal rocks was chemically differentiated very early in the planet’s history – Boyet and Carlson’s results suggest within the first 30 million years, or less than 1%, of Earth’s history. As such, this evidence fits the growing number of observations from the Moon and Mars that the early history of planets was a very violent one, where collisions with planetesimals, the release of radioactive heat, and the energy involved in separating a metallic core all provide enough energy to melt the planet. Cooling and crystallization of the molten planet over timescales of millions to a few tens of millions of years then result in its chemical differentiation, segregating material according to density. This differentiation left most of the Earth’s mantle similar in composition to the present-day upper mantle from which volcanic rocks are derived.

There must then be material that is complementary in composition to the bulk of the mantle. This complementary region, if the Earth is to have an average composition matching chondrites, must be enriched in potassium, uranium, and thorium -- radioactive elements that have provided most of the heat generation in the Earth’s interior throughout its history. Furthermore, this complementary mantle reservoir must be very deep, because none of the magmas that have erupted at the Earth’s surface have ever sampled it. Boyet and Carlson suggest that the reservoir coincides with the so-called D" layer imaged seismically at the very base of the mantle, just above the core. A radioactive-element-rich layer deep in the Earth is like a heating plate at the bottom of a pot: it will keep the bottom of the pot hot for a long time. Such a layer will also keep the top of the core hot and hence delay its cooling and crystallization. The scientists postulate that the early differentiation of the Earth and the deep layer produced by that process may be the reason that the Earth still has its magnetic field. The deep layer may also be responsible for generating hot plumes of upwelling mantle material that give rise to volcanic island chains such as Hawaii.

Maud Boyet | EurekAlert!
Further information:
http://www.dtm.ciw.edu
http://www.CarnegieInstitution.org

More articles from Earth Sciences:

nachricht The melting ice makes the sea around Greenland less saline
16.10.2017 | Aarhus University

nachricht WSU researchers document one of planet's largest volcanic eruptions
12.10.2017 | Washington State University

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Breaking: the first light from two neutron stars merging

Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.

Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....

Im Focus: Smart sensors for efficient processes

Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).

When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...

Im Focus: Cold molecules on collision course

Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.

How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...

Im Focus: Shrinking the proton again!

Scientists from the Max Planck Institute of Quantum Optics, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.

It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly...

Im Focus: New nanomaterial can extract hydrogen fuel from seawater

Hybrid material converts more sunlight and can weather seawater's harsh conditions

It's possible to produce hydrogen to power fuel cells by extracting the gas from seawater, but the electricity required to do it makes the process costly. UCF...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ASEAN Member States discuss the future role of renewable energy

17.10.2017 | Event News

World Health Summit 2017: International experts set the course for the future of Global Health

10.10.2017 | Event News

Climate Engineering Conference 2017 Opens in Berlin

10.10.2017 | Event News

 
Latest News

Study suggests oysters offer hot spot for reducing nutrient pollution

17.10.2017 | Life Sciences

Breaking: the first light from two neutron stars merging

17.10.2017 | Physics and Astronomy

World first for reading digitally encoded synthetic molecules

17.10.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>