Posted on 02/05/2007 2:38:10 PM PST by blam
Source: University of Chicago
Date: February 5, 2007
Ancient Rocks Show How Young Earth Avoided Becoming Giant Snowball
Science Daily — 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.
A rock from a banded iron formation in northern Quebec, Canada. The bands vary in thickness from approximately 10 microns (less than the width of a human hair), to 10 meters (30 feet). This sample is measures a few inches across. At 3.75 billion years of age, it is one of the oldest rocks on Earth. "These rocks, with meteorites, are the only time travel machines into the early history of our planet," said University of Chicago geoscientist Nicolas Dauphas. (Credit: Photo by Dan Dry)
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.
Note: This story has been adapted from a news release issued by University of Chicago.
Long odds that Earth could support life. All delicately arranged, seemingly.
What the Global Warming Thought Police and Al Gore-style morons fail to appreciate is that greenhouse gasses have resuscitated a totally frozen Snowball Earth on more than one occasion in the history of our planet.
From what I recall of the climate data from the mars rovers it seems that the warmest day they've seen was a steamy -25 degree summer day.
Granted it's further away but it's a good example of what getting rid of the CO2 can do for us.
Interesting photo, but it leaves lots of unanswered questions (IANAPG - I am not a paleogeologist). Assuming that the banded iron deposits are evidenced by the horizontal striations, what would be the cause of the lighter, angled coloration extending through those layers? It would not seem to be an indication of some other type of sediment. Perhaps it represents the effects of geologic forces acting on the sedimentary layers, indicative of twisting or upward thrusting forces? Or something else?
The Martian atmosphere is almost all CO2 and the warmest recorded temperature ever on Mars is about 40 degrees F. Not warm but not bad, it is a rare event tho
bump for later, thanks!
Guess I was thinking the CO2 was mostly locked up in the poles.
The Martian atmosphere is also only about 10 millibars of pressure (1% Earth). Not much CO2 or anything else there.
It also lacks the main greenhouse gas in the atmosphere. H2O
Oh man, I'm so glad I saw this story! I was just asking myself the other day, "How did the young earth avoid becoming a giant snowball?" I mean, it bugged me for the whole day -- I kept asking everyone at my office, calling my friends, but no one knew!
Wow, what a relief -- to finally find out the answer to that pressing question. Now, if someone could just tell me how teenage earth avoided becoming a massive fireball, my life will be complete!
A bane? Don't you mean a blessing?
No carbon dioxide = no plants.
No plants = no animals.
No plants + no animals = NO LIFE.
"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."
Does this or does this not sound like the C02 cycle acts as a natural thermostat on the atmosphere. During "cold" spells (ice ages) C02 accumulates in the atmosphere, which eventually produces a greenhouse affect, which produces a warm spell ("global warming"), which causes faster rate of the carbon sink affect, which decreases atmpospheric CO2 and temperature over time, leading to another "cold spell" which leads to another "warm spell", etc., etc., etc.
What then, if anything, can be the net "human affect" on this? It can only be the shortening of the time between the peaks and valleys of the cycle, and possibly addding the attainment of smaller peaks and valleys during those shorter cycles.
Which could mean, possibly, that any "warming" will end sooner than currently predicted, which will be followed by a cooling, which will only end in a shorter time if............we are still affecting the carbon release/carbon sink cycle.
If, instead, our activity increases the carbon sink during an upcoming warming (which reducing greenhouses gases will do), then the warming point in the cycle will last longer, and possibly reach higher temperatures before the atmospheric CO2 becomes high enough to trigger net additions to the carbon sink; that would bring in the cooling point in the cycle again.
Even if "human activity" is part of "global warming", the "global warming" political agenda could be the opposite of what we need to do; because of how C02 works as a natural thermostat. The warm cycles produce the C02 conditions leading to the next cool cycle and the cool cycles produce a C02 condition leading to the next warm cycle. The source (medium of exchange) is not important. Each cycle, cooling or warming, produces the C02 conditions for its reversal, based on the C02 balance, not how slowly or quickly it is obtained.
"..when astrophysicists believe the sun was 25 percent fainter than today."
There's my highlight of the article!
I'm surprised they don't mention it in this article, but I believe some of the oldest fossils (bacteria) can be found in some of the Canadian shield precambrian rock and date to almost 3.5 billion years ago.
may have
established with certainty
Ping.
Oh man, I'm so glad I saw this story! I was just asking myself the other day
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