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The latest Research, Reviews, News and information about Geology / Earth Science from around the web. GEOLOGY INFO
Simulated sunlight powers a solar cell that converts atmospheric carbon dioxide directly into syngas. Credit: University of Illinois at Chicago/Jenny Fontaine
Simulated sunlight powers a solar cell that converts atmospheric carbon dioxide directly into syngas. Credit: University of Illinois at Chicago/Jenny Fontaine
Researchers at the University of Illinois at Chicago have engineered a potentially game-changing solar cell that cheaply and efficiently converts atmospheric carbon dioxide directly into usable hydrocarbon fuel, using only sunlight for energy.

The finding is reported in the July 29 issue of Science and was funded by the National Science Foundation and the U.S. Department of Energy. A provisional patent application has been filed.

Unlike conventional solar cells, which convert sunlight into electricity that must be stored in heavy batteries, the new device essentially does the work of plants, converting atmospheric carbon dioxide into fuel, solving two crucial problems at once. A solar farm of such "artificial leaves" could remove significant amounts of carbon from the atmosphere and produce energy-dense fuel efficiently.

"The new solar cell is not photovoltaic -- it's photosynthetic," says Amin Salehi-Khojin, assistant professor of mechanical and industrial engineering at UIC and senior author on the study.

"Instead of producing energy in an unsustainable one-way route from fossil fuels to greenhouse gas, we can now reverse the process and recycle atmospheric carbon into fuel using sunlight," he said.

While plants produce fuel in the form of sugar, the artificial leaf delivers syngas, or synthesis gas, a mixture of hydrogen gas and carbon monoxide. Syngas can be burned directly, or converted into diesel or other hydrocarbon fuels.

The ability to turn CO2 into fuel at a cost comparable to a gallon of gasoline would render fossil fuels obsolete.

Chemical reactions that convert CO2 into burnable forms of carbon are called reduction reactions, the opposite of oxidation or combustion. Engineers have been exploring different catalysts to drive CO2 reduction, but so far such reactions have been inefficient and rely on expensive precious metals such as silver, Salehi-Khojin said.

"What we needed was a new family of chemicals with extraordinary properties," he said.

Salehi-Khojin and his coworkers focused on a family of nano-structured compounds called transition metal dichalcogenides -- or TMDCs -- as catalysts, pairing them with an unconventional ionic liquid as the electrolyte inside a two-compartment, three-electrode electrochemical cell.

The best of several catalysts they studied turned out to be nanoflake tungsten diselenide.

"The new catalyst is more active; more able to break carbon dioxide's chemical bonds," said UIC postdoctoral researcher Mohammad Asadi, first author on the Science paper.

In fact, he said, the new catalyst is 1,000 times faster than noble-metal catalysts -- and about 20 times cheaper.

Other researchers have used TMDC catalysts to produce hydrogen by other means, but not by reduction of CO2. The catalyst couldn't survive the reaction.

"The active sites of the catalyst get poisoned and oxidized," Salehi-Khojin said. The breakthrough, he said, was to use an ionic fluid called ethyl-methyl-imidazolium tetrafluoroborate, mixed 50-50 with water.

"The combination of water and the ionic liquid makes a co-catalyst that preserves the catalyst's active sites under the harsh reduction reaction conditions," Salehi-Khojin said.

The UIC artificial leaf consists of two silicon triple-junction photovoltaic cells of 18 square centimeters to harvest light; the tungsten diselenide and ionic liquid co-catalyst system on the cathode side; and cobalt oxide in potassium phosphate electrolyte on the anode side.

When light of 100 watts per square meter -- about the average intensity reaching Earth's surface -- energizes the cell, hydrogen and carbon monoxide gas bubble up from the cathode, while free oxygen and hydrogen ions are produced at the anode.

"The hydrogen ions diffuse through a membrane to the cathode side, to participate in the carbon dioxide reduction reaction," said Asadi.

The technology should be adaptable not only to large-scale use, like solar farms, but also to small-scale applications, Salehi-Khojin said. In the future, he said, it may prove useful on Mars, whose atmosphere is mostly carbon dioxide, if the planet is also found to have water.

"This work has benefitted from the significant history of NSF support for basic research that feeds directly into valuable technologies and engineering achievements," said NSF program director Robert McCabe.

"The results nicely meld experimental and computational studies to obtain new insight into the unique electronic properties of transition metal dichalcogenides," McCabe said. "The research team has combined this mechanistic insight with some clever electrochemical engineering to make significant progress in one of the grand-challenge areas of catalysis as related to energy conversion and the environment."

Source:
The above post is reprinted from materials provided by University of Illinois at Chicago.

Reference:
Mohammad Asadi et al. Nanostructured transition metal dichalcogenide electrocatalysts for CO2 reduction in ionic liquid. Science, July 2016 DOI: 10.1126/science.aaf4767
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The latest Research, Reviews, News and information about Geology / Earth Science from around the web. GEOLOGY INFO
Schematic diagram of the atmosphere. Credit: Graphics: C. Kersten, GEOMAR
Schematic diagram of the atmosphere. Credit: Graphics: C. Kersten, GEOMAR
Water plays a major role for our planet not only in its liquid form at the surface. In the atmosphere too, it considerably affects our lives as well as weather and climate. Clouds and rainfall are one example. Water vapor, the gaseous form of water, also plays a prominent role on Earth. It is the most important greenhouse gas in the atmosphere, without it the Earth would be a frozen planet. For climate variations, water vapor is particularly important in the stratosphere at altitudes between 15 and 50 kilometers. How much of the gas actually reaches the stratosphere mainly depends on the temperature at the transition between the lowest atmospheric layer, the troposphere, and the overlying stratosphere. This boundary layer is called the tropopause.

Now scientists of the GEOMAR Helmholtz Centre for Ocean Research Kiel, together with a colleague from Bergen (Norway), were able to demonstrate for the first time that natural fluctuations in water temperatures of the Pacific -- which occur on decadal timescales -- are directly related to the temperature of the tropical tropopause. "It has long been thought that human influences already affected the tropopause. However, it seems that natural variability is still the dominating factor," says Dr. Wuke Wang from GEOMAR, lead author of the study just published in the international journal Scientific Reports.

For their study, the researchers used observations for the period 1979-2013 and also climate models. "We were thus able to extend the study period to nearly 150 years. The model allows us to easily look at both human and natural influences and to separate their impacts from each other," explains Prof. Dr. Katja Matthes, climate researcher at GEOMAR and co-author of the study.

A well-known climatic phenomenon is the so-called Pacific Decadal Oscillation (PDO). "This natural variation with decadal timescale leads to anomalously high or low water temperatures of the Pacific," explained Dr. Wang. The PDO influences the climate and ecosystems in the Pacific region and also the global mean temperature of the Earth.

The model simulations show that the fluctuations in water temperatures also affect the wind systems over the tropical and subtropical Pacific. This in turn also alters the air transport between the lower and upper layers of the troposphere, ultimately regulating the temperatures at the boundary to the stratosphere. "We were now able to demonstrate these relationships for the first time," said Dr. Wang.

Thus, the current study contradicts earlier hypotheses about the temperature variability of the tropical tropopause. As early as in the late 20th century, scientists had seen a cooling trend there which began in the 1970s. They traced this observation back to anthropogenic causes, in particular the increase in greenhouse gases. "However, this assumption was based on a rather patchy data base and simplified climate models. Our study shows that the cooling of the tropical tropopause does not have to be a one-way street but could also be part of a natural fluctuation which extends over several decades," Professor Matthes emphasized.

This knowledge is also of paramount importance for the general climate research. The temperature of the tropopause decides on the input of water vapor into the stratosphere: The higher the water vapor content in the stratosphere, the higher the increase in surface temperatures. Anthropogenic climate change also has an effect on the temperature of the tropopause, and this effect could become more evident in the coming decades. "Only if we can clearly distinguish natural variability from anthropogenic influences, we can make reliable forecasts for the future development of our climate," Prof. Matthes summarizes.
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Source:
The above post is reprinted from materials provided by Helmholtz Centre for Ocean Research Kiel (GEOMAR).

Reference:
Wuke Wang, Katja Matthes, Nour-Eddine Omrani, Mojib Latif. Decadal variability of tropical tropopause temperature and its relationship to the Pacific Decadal Oscillation. Scientific Reports, 2016; 6: 29537 DOI: 10.1038/srep29537
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Climate Change. Credit: Jacob Braun / flickr
Climate Change. Credit: Jacob Braun / flickr
There is some consolation in how the fossil fuel-induced climatic changes we increasingly experience through droughts and storm surges are playing out. It could have happened sooner, and therefore already have been much worse.

Luckily, the natural atmosphere already contained carbon dioxide, enough that the human-induced changes were relatively small, for a long time. Had these concentrations been even slightly lower, the effects of the emission of harmful greenhouse gases would have been felt much earlier, at a time when humankind was not yet ready or knowledgeable enough to face up to mitigation efforts. This silver lining approach is taken by David Archer of the University of Chicago in the US, in a scenario exercise in Springer's journal Climatic Change.

The concentration of carbon dioxide molecules in the atmosphere is measured as parts per million of dry air, or ppm. In the climatic past and earlier glacial periods, this level fluctuated between 180 ppm and 260 ppm. Measurements taken of Antarctic sheet ice show that the concentration of naturally occurring carbon dioxide in the atmosphere was already 278 ppm in the 1750s before industrialization started in earnest.

"If the initial atmospheric carbon dioxide concentration were half its actual value, we would currently be experiencing the climate expected for the year 2050," says Archer, setting out one possible scenario. "If there were only one-tenth as much carbon dioxide in the atmosphere initially, the climate forcing we are experiencing today would have already happened, in the year 1900."

Archer therefore describes the climatic changes currently being experienced on Earth as "moderate," thanks to the blanketing effect that naturally occurring carbon dioxide in the atmosphere has had. This has given scientists the time to piece together an understanding of Earth's climate system and the effects of fossil fuel emissions.

The first ideas about radiative balance and the greenhouse effect date back to 1827, while predictions about climatic sensitivity due to carbon dioxide were made by 1896. It was, however, only after the advent of the computer that a modern understanding emerged of how fossil fuel use would impact the climate. This understanding was able to mature to the extent of public warnings about it by the 1970s.

"If the natural concentration had been a factor of two or more lower, the climate impacts of fossil fuel carbon dioxide release would have occurred about 50 or more years sooner, making it much more challenging for the developing human society to scientifically understand the phenomenon of humanmade climate change in time to prevent it," he says. "To the extent that a thorough scientific understanding is also a requisite for making a decision to abandon fossil fuels, the outlook for humanity would have been considerably darker in this altered world than it has turned out in actuality."
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Source:
The above post is reprinted from materials provided by Springer.

Reference:
David Archer. Near miss: the importance of the natural atmospheric CO2 concentration to human historical evolution. Climatic Change, 2016; DOI: 10.1007/s10584-016-1725-y
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The first six months of 2016 were the warmest six-month period in NASA's modern temperature record, which dates to 1880. Credit: NASA/Goddard Institute for Space Studies
The first six months of 2016 were the warmest six-month period in NASA's modern temperature record, which dates to 1880. Credit: NASA/Goddard Institute for Space Studies
Two key climate change indicators - global surface temperatures and Arctic sea ice extent - have broken numerous records through the first half of 2016, according to NASA analyses of ground-based observations and satellite data.

Each of the first six months of 2016 set a record as the warmest respective month globally in the modern temperature record, which dates to 1880, according to scientists at NASA's Goddard Institute for Space Studies (GISS) in New York. The six-month period from January to June was also the planet's warmest half-year on record, with an average temperature 1.3 degrees Celsius (2.4 degrees Fahrenheit) warmer than the late nineteenth century.

Five of the first six months of 2016 also set records for the smallest respective monthly Arctic sea ice extent since consistent satellite records began in 1979, according to analyses developed by scientists at NASA's Goddard Space Flight Center, in Greenbelt, Maryland. The one exception, March, recorded the second smallest extent for that month.

While these two key climate indicators have broken records in 2016, NASA scientists said it is more significant that global temperature and Arctic sea ice are continuing their decades-long trends of change. Both trends are ultimately driven by rising concentrations of heat-trapping carbon dioxide and other greenhouse gases in the atmosphere.

The extent of Arctic sea ice at the peak of the summer melt season now typically covers 40 percent less area than it did in the late 1970s and early 1980s. Arctic sea ice extent in September, the seasonal low point in the annual cycle, has been declining at a rate of 13.4 percent per decade.

"While the El Niño event in the tropical Pacific this winter gave a boost to global temperatures from October onwards, it is the underlying trend which is producing these record numbers," GISS Director Gavin Schmidt said.

Previous El Niño events have driven temperatures to what were then record levels, such as in 1998. But in 2016, even as the effects of the recent El Niño taper off, global temperatures have risen well beyond those of 18 years ago because of the overall warming that has taken place in that time.

The global trend in rising temperatures is outpaced by the regional warming in the Arctic, said Walt Meier, a sea ice scientist at NASA Goddard.

"It has been a record year so far for global temperatures, but the record high temperatures in the Arctic over the past six months have been even more extreme," Meier said. "This warmth as well as unusual weather patterns have led to the record low sea ice extents so far this year."

NASA tracks temperature and sea ice as part of its effort to understand the Earth as a system and to understand how Earth is changing. In addition to maintaining 19 Earth-observing space missions, NASA also sends researchers around the globe to investigate different facets of the planet at closer range. Right now, NASA researchers are working across the Arctic to better understand both the processes driving increased sea ice melt and the impacts of rising temperatures on Arctic ecosystems.

NASA's long-running Operation IceBridge campaign last week began a series of airborne measurements of melt ponds on the surface of the Arctic sea ice cap. Melt ponds are shallow pools of water that form as ice melts. Their darker surface can absorb more sunlight and accelerate the melting process. IceBridge is flying out of Barrow, Alaska, during sea ice melt season to capture melt pond observations at a scale never before achieved. Recent studies have found that the formation of melt ponds early in the summer is a good predictor of the yearly minimum sea ice extent in September.

"No one has ever, from a remote sensing standpoint, mapped the large-scale depth of melt ponds on sea ice," said Nathan Kurtz, IceBridge's project scientist and a sea ice researcher at NASA Goddard. "The information we'll collect is going to show how much water is retained in melt ponds and what kind of topography is needed on the sea ice to constrain them, which will help improve melt pond models."

Operation IceBridge is a NASA airborne mission that has been flying multiple campaigns at both poles each year since 2009, with a goal of maintaining critical continuity of observations of sea ice and the ice sheets of Greenland and Antarctica.

At the same time, NASA researchers began in earnest this year a nearly decade-long, multi-faceted field study of Arctic ecosystems in Alaska and Canada. The Arctic-Boreal Vulnerability Experiment (ABoVE) will study how forests, permafrost and other ecosystems are responding to rising temperatures in the Arctic, where climate change is unfolding faster than anywhere else on the planet.

ABoVE consists of dozens individual experiments that over years will study the region's changing forests, the cycle of carbon movement between the atmosphere and land, thawing permafrost, the relationship between fire and climate change, and more.
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The above post is reprinted from materials provided by NASA/Goddard Space Flight Center.
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Weather station. Credit: © ted007 / Fotolia
Weather station. Credit: © ted007 / Fotolia
A new NASA-led study finds that almost one-fifth of the global warming that has occurred in the past 150 years has been missed by historical records due to quirks in how global temperatures were recorded. The study explains why projections of future climate based solely on historical records estimate lower rates of warming than predictions from climate models.

The study applied the quirks in the historical records to climate model output and then performed the same calculations on both the models and the observations to make the first true apples-to-apples comparison of warming rates. With this modification, the models and observations largely agree on expected near-term global warming. The results were published in the journal Nature Climate Change. Mark Richardson of NASA's Jet Propulsion Laboratory, Pasadena, California, is the lead author.

The Arctic is warming faster than the rest of Earth, but there are fewer historic temperature readings from there than from lower latitudes because it is so inaccessible. A data set with fewer Arctic temperature measurements naturally shows less warming than a climate model that fully represents the Arctic.

Because it isn't possible to add more measurements from the past, the researchers instead set up the climate models to mimic the limited coverage in the historical records.

The new study also accounted for two other issues. First, the historical data mix air and water temperatures, whereas model results refer to air temperatures only. This quirk also skews the historical record toward the cool side, because water warms less than air. The final issue is that there was considerably more Arctic sea ice when temperature records began in the 1860s, and early observers recorded air temperatures over nearby land areas for the sea-ice-covered regions. As the ice melted, later observers switched to water temperatures instead. That also pushed down the reported temperature change.

Scientists have known about these quirks for some time, but this is the first study to calculate their impact. "They're quite small on their own, but they add up in the same direction," Richardson said. "We were surprised that they added up to such a big effect."

These quirks hide around 19 percent of global air-temperature warming since the 1860s. That's enough that calculations generated from historical records alone were cooler than about 90 percent of the results from the climate models that the Intergovernmental Panel on Climate Change (IPCC) uses for its authoritative assessment reports. In the apples-to-apples comparison, the historical temperature calculation was close to the middle of the range of calculations from the IPCC's suite of models.

Any research that compares modeled and observed long-term temperature records could suffer from the same problems, Richardson said. "Researchers should be clear about how they use temperature records, to make sure that comparisons are fair. It had seemed like real-world data hinted that future global warming would be a bit less than models said. This mostly disappears in a fair comparison."
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Source:
The above post is reprinted from materials provided by NASA/Jet Propulsion Laboratory.

Reference:
Mark Richardson, Kevin Cowtan, Ed Hawkins, Martin B. Stolpe. Reconciled climate response estimates from climate models and the energy budget of Earth. Nature Climate Change, 2016; DOI: 10.1038/nclimate3066
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Ocean. Researchers decipher the temperature indicator TEX86 and overcome a seeming weakness of global climate models. Credit: Copyright Michele Hogan
Ocean. Researchers decipher the temperature indicator TEX86 and overcome a seeming weakness of global climate models. Credit: Copyright Michele Hogan
Scientists from the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research (AWI) have overcome a seeming weakness of global climate models. They had previously not been able to simulate the extreme warm period of the Eocene. One aspect of this era that particularly draws interests to climatologists: It was the only phase in recent history when greenhouse gas concentration was as high as researchers predict it to be for the future. The AWI scientists have now found that the apparent model weakness is due to a misinterpretation of the temperature indicator TEX86. These molecules, which are produced by archaea do not record the surface temperature of the ancient ocean as expected, but rather the temperature of water depths up to 500 metres. In the current issue of the journal Nature Geoscience, the scientists report on this new finding which has now made it possible to correctly simulate the temperature distribution of the Eocene in climate models.

Climate scientists often hear the same complaint: How can climate models accurately predict the future of our planet if it is not even possible to correctly reproduce the climate of the past? One of the unsolved problems was that all previous attempts to simulate the extreme temperatures of the Eocene with climate models failed.

At that time, 49 to 55 million years ago, the carbon dioxide content of the air was likely more than 1000 ppm (parts per million) -- i.e. at least two times the current greenhouse gas concentration. The earth warmed up so strongly that the icesheets on Greenland and Antarctica disappeared. Instead of ice crystals, palm trees grew there. "Until recently, we believed that the sea surface temperature near the North Pole at the time was 23 degrees Celsius; in Antarctica, it was believed to have been more than 30 degrees Celsius," says Dr Thomas Laepple, climate researcher at the AWI Potsdam.

These temperature estimates were based on data from the climate indicator TEX86. This abbreviation stands for a ratio of specific organic compounds produced by archaea, depending on the water temperature in which they lived. "Archaea are unicellular organisms that can in part withstand surprisingly high ambient temperatures. The molecules of the organisms that were living at that time are still preserved in the sedimentary layers of the seafloor. They are one of our most important archives for warm climate conditions, but as we have seen, we decoded them wrongly in the past," says Thomas Laepple.

He and his AWI colleague at the time, Sze Ling Ho, first had doubts about the interpretation of the TEX86 temperature indicator during a comparison of climate data from the most recent ice age. The scientists noticed that the TEX86 temperatures were far too cold compared to other geological evidence. "The discrepancy was so obvious that we started to review the TEX86 values of around 3,000 sediment samples from different ocean basins and from different epochs of the Earth. It soon became apparent that the average temperature change inferred from TEX86 was exaggerated, always and on all time scales, by one and a half to two times. The temperature it showed for cold periods was much too cold and the one for warm periods was much too warm," explains geochemist Sze Ling Ho.

The cause of this pattern had to be of a fundamental nature, a suspicion that was confirmed upon closer analysis. "TEX86 had previously been interpreted as an indicator of sea surface temperature, in spite the fact that the archaea that produce TEX86 rarely directly live at the sea surface. Through the comparison with other climate archives, we have been able to constrain the depth in which the TEX86 signal is produced. We now assume that TEX86 represents the water temperature at a depth of up to 500 metres," Sze Ling Ho explains.

At this water depth, the temperature difference between the tropical oceans and the polar seas is smaller than at the surface. This has direct consequences for climate reconstruction, since the information generated from the indicator is differently translated into temperature values. "In practice, the TEX86 extreme values need to be roughly halved in the climate reconstructions. Comparing the corrected temperatures with the models shows that they now reflect the climate of the Eocene in a realistic and physically consistent way," explains Thomas Laepple.

However, we also have to correct our temperature-conception of the Eocene. Thomas Laepple: "The era remains the warmest period of the past 65 million years. The water temperatures that we assumed for the Arctic and Antarctica, though, were overstated by at least ten degrees Celsius. Now, we know that the water in the Southern Ocean had a temperature of about 20 to 25 degrees Celsius at that time. The region was therefore still warm enough for there to be palm trees sprouting on the beach."
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Source:

Reference:
Sze Ling Ho, Thomas Laepple. Flat meridional temperature gradient in the early Eocene in the subsurface rather than surface ocean. Nature Geoscience, 2016; DOI: 10.1038/NGEO2763
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A much faster pace of evolution means that species could have proliferated much more rapidly than they do now, affording the flora and fauna of Earth ample time to acquire their enormous diversity and complexity. Credit: © somchaisom / Fotolia
A much faster pace of evolution means that species could have proliferated much more rapidly than they do now, affording the flora and fauna of Earth ample time to acquire their enormous diversity and complexity. Credit: © somchaisom / Fotolia
Early life forms on Earth are likely to have mutated and evolved at much higher rates than they do today, suggests a new analysis from researchers at the University of North Carolina.

In a study published this week in the Proceedings of the National Academy of Sciences, Richard Wolfenden, PhD, and his colleagues found that the rate of a certain chemical change in DNA -- a key driver of organisms' spontaneous mutation rates and thus of evolution's pace -- increases extremely rapidly with temperature. Combining that finding with recent evidence that life arose when our planet was much warmer than it is now, the scientists concluded that the rate of spontaneous mutation was at least 4,000 times higher than it is today.

"At the higher temperatures that seem to have prevailed during the early phase of life, evolution was shaking the dice frantically," said Wolfenden, Alumni Distinguished Professor of Biochemistry and Biophysics at the UNC School of Medicine.

A much faster pace of evolution means that species could have proliferated much more rapidly than they do now, affording the flora and fauna of Earth ample time to acquire their enormous diversity and complexity.

That issue -- whether life could have evolved to its present level of complexity within the time available -- has lingered ever since Darwin published his theory more than a century and a half ago. Throughout that debate, both skeptics and proponents of evolutionary theory have often assumed that evolution's pace has stayed more or less constant over the eons.

The planet formed about 4.6 billion years ago from the cloud of dust and gas surrounding the early sun, and began as a hellish world of molten rock. It cooled until a crust condensed, and eventually, around 4.3 billion years ago, liquid brine began to fill the lower elevations, forming oceans.

"Recent evidence from rock samples in Australia indicates that life forms arose on Earth as early as 4.1 billion years ago -- almost in the blink of an eye after the appearance of liquid oceans," Wolfenden said.

At that time, the average temperature at Earth's surface would have been near the boiling point of water -- 100 degrees Celsius, about 75 degrees higher than today.

To get some idea of the effect of such a high temperatures on the rate of evolution, Wolfenden's team examined a chemical reaction known as cytosine deamination, which occurs from time to time in all cells and may be the single most frequent cause of spontaneous DNA mutations.

In the deamination reaction, cytosine -- the DNA base molecule known as "C" in the genetic code -- loses an ammonia-like "amine" group of atoms. Deamination leads to the mutation of the cytosine into the DNA base thymine ("T" in the genetic code).

Wolfenden's team experimentally determined the rates of spontaneous deamination at different temperatures for cytosine and several cytosine-related molecules. In collaboration with the UNC lab of Ronald Swanstrom, PhD, the Charles P. Postelle, Jr. Distinguished Professor of Biochemistry at UNC, the researchers also measured the rates of cytosine deaminations and spontaneous C-to-T mutations in single-stranded DNA from the HIV virus that causes AIDS. The results showed that the rates of cytosine deamination, for isolated molecules and for single-stranded DNA, rose very steeply as the temperature increased. The scientists then added the assumption that Earth's surface temperature has itself changed exponentially -- following Newton's law of cooling -- over the period in which life has existed.

"Cytosine-based mutations, when the temperature was near 100 degrees C, occurred at more than 4,000 times the modern rate,"Wolfenden said. "To me, that was surprising. I thought the ancient rate would be more rapid than the modern rate, but not that rapid."

How could early life forms have coped with a high-temperature environment where their genetic material was being altered so rapidly?

"That question is still out there," Wolfenden said. He noted, though, that there are microorganisms even now that normally live in hot springs or deep-sea thermal vents, and somehow survive and multiply at temperatures as high as 120 degrees C.

Originally, DNA was stabilized to some extent by the presence of a complementary strand of DNA, and as life forms evolved, they developed increasingly sophisticated mechanisms for repairing DNA damage.

"These findings give us some idea of the burden faced by primordial organisms before they evolved sophisticated systems for repair," Wolfenden said. "And they offer another clue about how evolution kick-started the creation of the diverse world we see today."
***

Source:
The above post is reprinted from materials provided by University of North Carolina Health Care System.
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