Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Ancient rocks show how young Earth avoided becoming giant snowball

07.02.2007
Carbon dioxide may have acted as planet's 'thermostat' since earliest times

A greenhouse gas that has become the bane of modern society may have saved Earth from completely freezing over early in the planet's history, according to the first detailed laboratory analysis of the world's oldest sedimentary rocks.

Scientists have for years theorized that high concentrations of greenhouse gases could have helped Earth avoid global freezing in its youth by allowing the atmosphere to retain more heat than it lost. A team at the University of Chicago and the University of Colorado has now analyzed ancient rocks from the eastern shore of Hudson Bay in northern Quebec, Canada, which has yielded the first preliminary field evidence supporting this theory.

"Our study shows the greenhouse gas that could have sustained surface temperatures above freezing 3.75 billion years ago may have been carbon dioxide," said Nicolas Dauphas, Assistant Professor in Geophysical Sciences at the University of Chicago. Dauphas and his co-authors, Nicole Cates and Stephen Mojzsis of the University of Colorado, and Vincent Busigny, now of the Institut de Physique du Globe in Paris, present their data in the Feb. 28 issue of the journal Earth and Planetary Science Letters.

In a companion article in the same issue of the journal, Cates and Mojzsis establish with certainty the antiquity of the rocks and discuss their origin in a wider context.

The study led by Dauphas helps explain how the Earth may have avoided becoming frozen solid early in its history, when astrophysicists believe the sun was 25 percent fainter than today. Previous studies had shown that liquid water existed at the Earth's surface even though the weak sun should have been unable to warm the Earth above freezing conditions. But high concentrations of carbon dioxide or methane could have warmed the planet.

Discovered in 2001 by a team of Canadian scientists, the Quebec rocks are among the oldest-known in Earth's 4.5-billion-year history. Slow-acting geologic processes destroy and recycle the Earth's crust on vast time scales, leaving only scraps of land containing remains of the planet's oldest rock.

The only other outcropping of rocks that are about as old occur in western Greenland. Scientists have studied those rocks exhaustively for more than three decades. But the limited extent of the rocks of this antiquity may have provided only a biased view of the early Earth, Dauphas said.

Mojzsis and Cates revisited the Canadian site to pursue new but as yet unrealized opportunities for analysis and comparison. Today Mojzsis describes the area as a landscape of rolling hills of grass and marsh, punctuated by lakes, streams and craggy rock outcroppings. Stunted trees of willow grow no more than six feet high, leaving unobstructed views all around.

"It is a grand landscape of water, wind and rock carved by glaciers and only lightly touched by the people who live there," Mojzsis said. But the region would have looked much different 3.8 billion years ago.

"At that time it would have appeared to be a totally alien world to us, with a dense atmosphere of carbon dioxide and methane that would have imparted a reddish cast to the sky, and deep dark greenish-blue oceans of iron-rich water washing onto beaches of small continents scattered across the globe," Mojzsis said.

The Chicago-Colorado scientists focused their analysis on rocks they suspected contained chemical sediments that precipitate like salt from seawater. "A critical issue with these rocks is that they have been cooked and deformed during burial in the crust for several hundred million years, which makes it difficult to identify their nature," Dauphas said.

First they dissolved the rock, separating iron oxides and iron carbonates from other constituents. Then they used a mass spectrometer to measure the isotopic composition of the iron. All iron atoms have 26 protons at their core, but they can be accompanied by a varying number of more numerous neutrons.

"Iron has several isotopes, and the ratio of these isotopes changes from one to another," Dauphas explained. "Sediments that formed by precipitation from seawater have a very distinct signature of iron isotopes." When the Chicago scientists analyzed the iron composition of the rocks, "We found that indeed they had the typical signature of something that formed by precipitation in a marine setting."

The iron probably was released with other metals in hydrothermal vents called black smokers found along mid-ocean ridges, where molten lava emerges on the sea floor to create new oceanic crust. In today's oxygen-rich oceans, the iron rapidly precipitates and concentrates near these vents. But in the oxygen-starved oceans of 3.8 billion years ago, oceanic currents could transport the iron long distances before becoming partially oxidized and deposited in sea-floor sediments.

Some of these sediments survive today as banded iron formations. "There are no banded iron formations being produced at present because there is too much oxygen," Dauphas said.

Previous research on the rocks from Greenland had already revealed the existence of ocean water at that early stage in Earth history, known as the Precambrian Period. But the Canadian rocks showed something else: the first hints that Precambrian oceans also contained iron carbonates. Iron carbonates can only form in an atmosphere that contains far higher levels of carbon dioxide than are found in Earth's atmosphere today, Dauphas said. This carbon dioxide would have played an important role as a planetary thermostat in the support of life on Earth.

"If it gets cold, ice caps form, chemical weathering decreases, carbon dioxide accumulates in the atmosphere, which increases the greenhouse effect and surface temperatures. If it gets hot, the rate of chemical weathering increases, the rate of burial of sedimentary carbonates increases, the amount of carbon dioxide in the atmosphere and surface temperatures decrease," Dauphas said.

Other factors are involved in this simplified scheme. "Still, it is possible that such a thermostat was at work as early as 3.75 billion years ago," he said.

Steve Koppes | EurekAlert!
Further information:
http://www.uchicago.edu

More articles from Earth Sciences:

nachricht Clear as mud: Desiccation cracks help reveal the shape of water on Mars
20.04.2018 | Geological Society of America

nachricht Hurricane Harvey: Dutch-Texan research shows most fatalities occurred outside flood zones
19.04.2018 | European Geosciences Union

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Spider silk key to new bone-fixing composite

University of Connecticut researchers have created a biodegradable composite made of silk fibers that can be used to repair broken load-bearing bones without the complications sometimes presented by other materials.

Repairing major load-bearing bones such as those in the leg can be a long and uncomfortable process.

Im Focus: Writing and deleting magnets with lasers

Study published in the journal ACS Applied Materials & Interfaces is the outcome of an international effort that included teams from Dresden and Berlin in Germany, and the US.

Scientists at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) together with colleagues from the Helmholtz-Zentrum Berlin (HZB) and the University of Virginia...

Im Focus: Gamma-ray flashes from plasma filaments

Novel highly efficient and brilliant gamma-ray source: Based on model calculations, physicists of the Max PIanck Institute for Nuclear Physics in Heidelberg propose a novel method for an efficient high-brilliance gamma-ray source. A giant collimated gamma-ray pulse is generated from the interaction of a dense ultra-relativistic electron beam with a thin solid conductor. Energetic gamma-rays are copiously produced as the electron beam splits into filaments while propagating across the conductor. The resulting gamma-ray energy and flux enable novel experiments in nuclear and fundamental physics.

The typical wavelength of light interacting with an object of the microcosm scales with the size of this object. For atoms, this ranges from visible light to...

Im Focus: Basel researchers succeed in cultivating cartilage from stem cells

Stable joint cartilage can be produced from adult stem cells originating from bone marrow. This is made possible by inducing specific molecular processes occurring during embryonic cartilage formation, as researchers from the University and University Hospital of Basel report in the scientific journal PNAS.

Certain mesenchymal stem/stromal cells from the bone marrow of adults are considered extremely promising for skeletal tissue regeneration. These adult stem...

Im Focus: Like a wedge in a hinge

Researchers lay groundwork to tailor drugs for new targets in cancer therapy

In the fight against cancer, scientists are developing new drugs to hit tumor cells at so far unused weak points. Such a “sore spot” is the protein complex...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

Invitation to the upcoming "Current Topics in Bioinformatics: Big Data in Genomics and Medicine"

13.04.2018 | Event News

Unique scope of UV LED technologies and applications presented in Berlin: ICULTA-2018

12.04.2018 | Event News

IWOLIA: A conference bringing together German Industrie 4.0 and French Industrie du Futur

09.04.2018 | Event News

 
Latest News

Scientists re-create brain neurons to study obesity and personalize treatment

20.04.2018 | Health and Medicine

Spider silk key to new bone-fixing composite

20.04.2018 | Materials Sciences

Clear as mud: Desiccation cracks help reveal the shape of water on Mars

20.04.2018 | Earth Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>