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!
Novel method for investigating pore geometry in rocks
18.06.2018 | Kyushu University, I2CNER
Decades of satellite monitoring reveal Antarctic ice loss
14.06.2018 | University of Maryland
In a recent publication in the renowned journal Optica, scientists of Leibniz-Institute of Photonic Technology (Leibniz IPHT) in Jena showed that they can accurately control the optical properties of liquid-core fiber lasers and therefore their spectral band width by temperature and pressure tuning.
Already last year, the researchers provided experimental proof of a new dynamic of hybrid solitons– temporally and spectrally stationary light waves resulting...
Scientists from the University of Freiburg and the University of Basel identified a master regulator for bone regeneration. Prasad Shastri, Professor of...
Moving into its fourth decade, AchemAsia is setting out for new horizons: The International Expo and Innovation Forum for Sustainable Chemical Production will take place from 21-23 May 2019 in Shanghai, China. With an updated event profile, the eleventh edition focusses on topics that are especially relevant for the Chinese process industry, putting a strong emphasis on sustainability and innovation.
Founded in 1989 as a spin-off of ACHEMA to cater to the needs of China’s then developing industry, AchemAsia has since grown into a platform where the latest...
The BMBF-funded OWICELLS project was successfully completed with a final presentation at the BMW plant in Munich. The presentation demonstrated a Li-Fi communication with a mobile robot, while the robot carried out usual production processes (welding, moving and testing parts) in a 5x5m² production cell. The robust, optical wireless transmission is based on spatial diversity; in other words, data is sent and received simultaneously by several LEDs and several photodiodes. The system can transmit data at more than 100 Mbit/s and five milliseconds latency.
Modern production technologies in the automobile industry must become more flexible in order to fulfil individual customer requirements.
An international team of scientists has discovered a new way to transfer image information through multimodal fibers with almost no distortion - even if the fiber is bent. The results of the study, to which scientist from the Leibniz-Institute of Photonic Technology Jena (Leibniz IPHT) contributed, were published on 6thJune in the highly-cited journal Physical Review Letters.
Endoscopes allow doctors to see into a patient’s body like through a keyhole. Typically, the images are transmitted via a bundle of several hundreds of optical...
13.06.2018 | Event News
08.06.2018 | Event News
05.06.2018 | Event News
20.06.2018 | Materials Sciences
20.06.2018 | Materials Sciences
20.06.2018 | Materials Sciences