Professor uses volcanic emissions to study Earth’s atmospheric past

On March 20, Iceland’s Eyjafjallajokull volcano woke from its nearly 200-year slumber to change the way the world viewed volcanoes forever. Bringing almost all transatlantic air travel to a halt for the first time in modern history, this volcano reminded humanity of the powers these forces of nature contain – and of our relative inability to understand them. Associate Professor Huiming Bao of LSU’s Department of Geology & Geophysics has published research in the journal Nature about massive volcanic eruptions and their atmospheric consequences in the past in North America.

“Past volcanic eruptions have had significant impacts on the environment,” said Bao. “We humans have witnessed the various impacts of volcanic eruptions like the 1991 Mount Pinatubo and the more recent Icelandic one. The physical aspect of the impacts such as explosion or ash plumes is often short-lived, but the chemical consequence of its emitted massive gases can have a long-lasting effect on global climate.”

The paper, titled “Massive Volcanic SO2 Oxidation and Sulfate Aerosol Deposition in Cenozoic North America,” represents research into the Earth’s climactic past. Using computer models and geological data, Bao and his colleagues, Shocai Yu of the EPA and Daniel Tong of the National Oceanic and Atmospheric Administration, or NOAA, were able to simulate the sulfur gas oxidation chemistry and atmospheric condition of the northern high plains region of North America long before human activities began significantly impact the air quality. Yu and Tong contributed to the modeling aspect of the study. They used a state-of-the-art atmospheric sulfur chemistry and transport model to simulate the atmospheric conditions necessary for the observed sulfate isotope data preserved in rock records.

Bao and his colleagues discovered that many of the volcanic ash beds are rich in sulfate, the product of atmospheric oxidation of sulfur gases. Most importantly, these sulfates have distinct stale isotope signatures that can tell how they were formed in the atmosphere, particularly which oxidation pathways they went through. In order to explain their geological data, they did an extensive modeling test and found that it is imperative to have an initial alkaline cloudwater pH condition, which rarely exists in modern days.

According to Bao, the most important volcanic gas – as far as atmospheric implications go – is sulfur dioxide, or SO2. This gas is oxidized in the atmosphere, where it is turned into sulfate aerosol, which plays a very sensitive role in the rate and impact of climate change. When the sulfate aerosol is dense or long-lasting and the depositional condition is right, the sulfate aerosol can be preserved in rock records.

“These sulfate aerosol deposition events were so intense that the sulfate on the ground or small ponds reached saturation and gypsum mineral formed,” Bao said. He pointed out that the closest analog event is perhaps the 1783 Laki eruptions of Iceland and the subsequent “dry fogs” in continental Europe. “That event devastated Iceland’s cattle population. People with lung problems suffered the worst. In North America, the next year’s winter was the longest and one of the coldest on record. The Mississippi River froze at New Orleans. The French Revolution in 1789 may have been triggered by the poverty and famine caused by the eruption.”

These explosive eruptions are much more intense and sulfur rich than any human has ever experienced or recorded. But that doesn’t mean that eruptions of such magnitude can’t happen today.

“It is important to note that the volcanic eruptions we experienced in the past thousands of years are nothing compared to some of the eruptions occurred in the past 40 million years in western North America, either in the level of power or the amount of SO2 spewed,” said Bao. “What we reported in our Nature paper is that there were many massive volcanic SO2 emissions and dense sulfate aerosol events in the northern High Plains of North America in the past. We show that in the past the sulfate aerosol formed in a very different way than today, indicating a difference in the past atmospheric condition or something peculiar with these explosive eruptions in the west.”

Volcanic eruptions in North America were more explosive in ancient past

Multiple ancient volcanic ash beds exposed at Scotts Bluff in Nebraska. - Credit: Huiming Bao
Multiple ancient volcanic ash beds exposed at Scotts Bluff in Nebraska. – Credit: Huiming Bao

Millions of years ago, volcanic eruptions in North America were more explosive and may have significantly affected the environment and the global climate. So scientists report in this week’s issue of the journal Nature.

The researchers found the remains–deposited in layers of rocks–of eruptions of volcanoes located on North America’s northern high plains that spewed massive amounts of sulfate aerosols into the atmosphere 40 million years ago. The scientists conducted their research at Scotts Bluff National Monument, Neb., and in surrounding areas.

“Combining measurements of the sulfate in ancient volcanic ash beds with a detailed atmospheric chemistry model, we found that the long-ago chemistry of volcanic sulfate gases is distinct from that of more modern times,” says Huiming Bao, a geologist at Louisiana State University and lead author of the paper.

“This is the first example showing that the history of massive volcanic sulfate emissions, and their associated atmospheric conditions in the geologic past, may be retrieved from rock records.”

Volcanic eruptions may have significant impacts on the environment, Bao says, citing the 1991 Mt. Pinatubo and more recent Iceland volcanic eruptions.

“The physical impacts of these eruptions, such as ash plumes, are relatively short-lived, but the chemical consequences of the emitted gases may have long-lasting effects on global climate,” says Sonia Esperanca, program director in the National Science Foundation (NSF)’s Division of Earth Sciences, which funded the research.

One of the most important volcanic gases is sulfur dioxide. It is oxidized in the atmosphere and turned to sulfate aerosol. This aerosol plays an important role in climate change.

“The volcanic eruptions of the last several thousand years hardly compare with some of the eruptions in the past 40 million years in western North America, especially in the amount of sulfur dioxide those eruptions spewed out,” says Bao.

What’s more important, he says, is that the formation of sulfate aerosol is related to atmospheric conditions at the time of a volcano’s eruption.

In the Nature paper, he and colleagues show that past sulfate aerosol formed in a different way than it does today, indicating a change from atmospheric conditions then to now.

A similar volcanic event to the long-ago past likely will happen again, Bao says: in the next Yellowstone eruption.

The closest analog, Bao believes, is the 1783 Laki, Iceland, eruption and the subsequent “dry fogs” in continental Europe.

That event devastated Iceland’s cattle population. People with lung problems suffered the worst, he says.

In North America, the very next year’s winter, that of 1784, was the longest and one of the coldest on record. The Mississippi River froze as far south as New Orleans. The French Revolution in 1789 may have been triggered by the poverty and famine caused by the eruption, scientists believe.

“Millions of years ago, volcanic eruptions in North America were more explosive,” Bao says, “and the quantity of sulfur dioxide released was probably hundreds of times more–greater even than in Laki in 1783.”

Delineating primary and secondary organic carbon in neoproterozoic glacial sediments

How do we begin to understand what early life was like on Earth about 700 million years ago as our planet shifted from an oxygen-free and probably ice-covered realm to the oxygen-rich world that we know today?

One geochemist who decodes the early record of life on Earth has found a method featuring a combination of chemical analysis for a significantly clearer picture of this dynamic environment. Alison Olcott Marshall of the University of Kansas presented her findings today at the Goldschmidt Conference in Knoxville, Tenn. The conference is attended by several thousand geochemists and features new scientific discoveries regarding the Earth, energy and the environment. It is hosted by the University of Tennessee, Knoxville, and Oak Ridge National Laboratory.

Marshall is particularly interested in the time called Snowball Earth, a period at the end of the Precambrian Era when geochemists speculate that the world was covered from pole to pole with glacial ice and the existing organisms lived exclusively in water. At that time life was still primarily single-cell organisms. So Marshall looks at chemical fossils to recreate the environment. The chemical complexes left from the cell walls of these organisms are more abundant and more easily classified than body fossils within the samples.

Marshall’s research carries her to southeast Brazil, where there is stable sedimentary rock from the late Precambrian era. Her samples come from exploratory drilling that reached eight hundred meters down into the core of black shale that was at
the bottom of a sea 700 million years ago.

“The one caveat with biomarkers (chemical fossils) is that there is always a danger of contamination,” Marshall said. Her initial tests using an instrument that looks at chemical compounds by molecular weight often had questionable results due to the possibility of contamination from material of a later period. However, by using another type of high resolution analysis called Raman spectroscopy, she also measured the subtle nuances of vibration that occur at the molecular level. Her high resolution results revealed two previously undetected distinctions in time generations.

Study begins on air-sea exchanges and their influence on climate

A two-year project, which will provide vital information on the interaction between the ocean and the atmosphere and its influence on climate, begins this month.

Scientists at the National Oceanography Centre (NOC), University of Leeds, and the British Antarctic Survey (BAS) are collaborating on the ‘Waves, Aerosols and Gas Exchange Study’ (WAGES), which begins this month with the installation of an autonomous air-sea flux system, ‘AutoFlux’, on the Royal Research Ship James Clark Ross, operated by BAS. The Autoflux makes continuous direct measurements of the air-sea exchange of carbon dioxide, sea-spray aerosol, heat, moisture, and momentum.

WAGES is a joint scientific project between the NOC, led by Dr Margaret Yelland and Professor Meric Srokosz, and the University of Leeds, led by Dr Ian Brooks. BAS is providing technical and logistical support.

“Sea spray aerosol is important for cloud formation, and the exchange of carbon dioxide and other gases between the sea and the atmosphere has an important impact on climate,” explained Margaret Yelland.

“These exchanges are not well understood, but are thought to depend on the type of waves that are present on the sea surface. For example, it may be that short steep waves produce more wave breaking and hence more gas transfer and aerosols than less steep waves. Similarly, wave breaking may be influenced by the sea surface temperature or the air-sea temperature difference,” added Ian Brooks.

Summer 2010 will see a commercial wave radar system added to obtain information on wave direction, along with digital cameras to image whitecap coverage. All systems will remain on the RRS James Clark Ross until at least the autumn of 2012.

In addition to the continuous flux and wave measurements, there will be a number of cruises during which WAGES personnel will deploy a spar buoy to obtain data on wave breaking. An aerial camera system will be flown by kite to obtain simultaneous wide-area whitecap coverage.

WAGES aims to continue and expand the work begun under three UK-SOLAS (Surface Ocean Lower Atmosphere Study) projects of limited duration or scope. Previous projects SEASAW and DOGEE only made measurements during relatively short research cruises, while HiWASE made three years of measurements from the weather ship Polarfront stationed at a single location in the North Atlantic.

“The exciting thing about WAGES is that it will obtain two years of data over the entire length of the Atlantic under a vast range of different conditions,” said Margaret Yelland:

“Measurements will be taken in sea-ice covered areas of the Antarctic and Arctic, the extreme seas of the Southern Ocean, the high temperatures of the equatorial Atlantic, and during the fierce storms of the North Atlantic.”

ESA makes first GOCE dataset available

The first products based on GOCE satellite data are now available online through ESA’s Earth observation user services tools. ESA launched the satellite in March 2009 on a mission to map Earth’s gravity with unprecedented accuracy and spatial resolution.

The final gravity map and model of the geoid based on GOCE data will provide users with well-defined products that will be instrumental in advancing science and applications in a broad range of disciplines.
However, there are a number of steps that have to be taken in order to turn the raw data into suitable products for users.

Raw data are downlinked from GOCE to the ground stations in Kiruna, northern Sweden, and on Svalbard, Norway. They are immediately forwarded to the Flight Operations Segment at ESA’s European Space Operations Centre (ESOC) in Darmstadt, Germany, which then links them through to the Payload Data Ground Segment at ESA’s European Space Research Institute (ESRIN) in Frascati, Italy. Here, through a process of calibration and validation, the data undergo an important transformation from telemetry to ‘level-1b’ data products.

Level-1b products are the time series of converted, calibrated and validated measurements taken by GOCE. They consist mainly of the gravity gradients in the instrument reference system and the orbit data (satellite-to-satellite tracking observations, positions and velocity) in an Earth-fixed coordinate system.

In addition, satellite data such as the attitude of the spacecraft and other housekeeping data complete the level-1b data.

These level-1b data, covering the period 1-30 November 2009, are available free of charge to scientific and non-commercial users, and much more will come in the following weeks and months.

“After an intensive calibration and validation phase, we are all very happy to see the science community at large getting involved in the exploitation of the data,” ESA GOCE Mission Manager Rune Floberhagen said.

“GOCE is proving to be a remarkable Earth science mission and we are more than confident that these data will not only change the way we see the gravity field of our planet but also the way the gravity field information is used in many branches of the geosciences.”

Subsequently, these level-1b data will be processed to level-2 through the High-level Processing Facility (HPF). Under ESA’s control, 10 European universities and research facilities that have complementary expertise in gravity and geodesy-related science fields, have joined together and will be operating the HPF throughout GOCE’s lifetime.

The first gravity field model (level-2 data) will be released at ESA’s Living Planet Symposium in Bergen, Norway, from 28 June to 2 July.

“The Living Planet Symposium will in many ways be a coming-out event for GOCE. We will spend two full days on the findings of the mission so far, and we certainly expect the release of our first gravity model to mark the beginning of a long and successful series of gravity field models based on GOCE’s novel measurement techniques,” Floberhagen said.

The final gravity map and model of the geoid will provide users with well-defined data products that will be instrumental in advancing science and applications in a broad range of disciplines, ranging from geodesy, geophysics and surveying to oceanography and sea-level research.

Storm elves and sprites recorded on video

This series of images shows the clash of two elves captured at high speed during a storm in December 2009. -  Montanyà et al.
This series of images shows the clash of two elves captured at high speed during a storm in December 2009. – Montanyà et al.

A team of Spanish researchers has made a high-speed recording of elves and sprites in storms, fleeting and luminous electric phenomena produced in the upper layers of the atmosphere. Their analysis of these observations has been published in the Journal of Geophysical Research.

“This is the first time in Europe that we have been able to use high-speed video to detect transitory luminous phenomena taking place in the upper atmosphere – so-called sprites (in the form of a carrot or column) and elves (which are ring shaped)”, Joan Montanyà, co-author of the study and a researcher at the Department of Electric Energy at the Polytechnic University of Catalonia (UPC), tells SINC.

The results have been published in the Journal of Geophysical Research and show there are many fewer elves in storms that form over land than those at sea, where electric currents apparently have greater energy, especially in winter. Some of the recordings show elves and sprites at the same time, evidence of the strength of lightning over the sea during winter storms.

The scientists also observed the interaction between two sprites. A branch of one of them hit and bounced off the second, giving clues about their dynamics and electric structure. Sprites normally appear for around 40 milliseconds and 20 or 30 kilometres away from the site of the lightning.

“All these phenomena are related with storms, particularly winter storms, but they only appear in mesoscale convective systems (usually in large fronts), which produce lightning with high levels of energy or extreme electric currents”, explains Montanyà.

As it is difficult to record these phenomena in situ during storms, the researchers placed a high-speed video camera on land with an image intensifier. This was used to remotely record a winter storm in the Western Mediterranean (at a distance of between 400 and 1,000 kilometres) between the coasts of Italy and Spain.

The physics of electric discharges

“The observations made it possible not only to capture images of these short duration events, but also mean we can study the structure and dynamics of these highly unique electric discharges”, explains Montanyà.

“Understanding the physics behind lightning and events associated with it will help us to protect ourselves better”, the scientist points out, stressing the importance of research into sprites and elves to better understand other phenomena, such as gamma rays from terrestrial sources (TGF, Terrestrial Gamma-ray Flash), which also develop above electric storms.

In fact, the European Space Agency (ESA)’s future Atmosphere-Space Interactions Monitor mission (ASIM) aims to monitor these phenomena by placing an instrument on the outside of the International Space Station, due to be launched in 2013.

A cooler Pacific may have severely affected medieval Europe, North America

Robert Burgman
Robert Burgman

In the time before Columbus sailed the ocean blue, a cooler central Pacific Ocean has been connected with drought conditions in Europe and North America that may be responsible for famines and the disappearance of cliff dwelling people in the American West.

A new study from the University of Miami (UM) has found a connection between La Niña-like sea surface temperatures in the central Pacific and droughts in western Europe and in what later became the southwestern United States and Mexico, as published in a recent issue of Geophysical Research Letters.

“We’ve known for some time the connection between El Niño and La Niña and the weather conditions in North America and Europe,” said Robert Burgman, a climate scientist at UM’s Rosenstiel School of Marine & Atmospheric Science. “La Niña-like conditions, such as those we found, can cause persistent drought, and as we know warm conditions cause increased precipitation.”

Using cores of fossil coral from the Palmyra Atoll in the central Pacific Ocean, Burgman and a team used reconstructed sea surface temperatures from the period 1320 to 1462 to simulate medieval climate conditions with a state-of-the-art climate model. When the differences between medieval and modern climate simulations were compared with paleo-records like tree-rings and sediment cores from around the globe, the authors found remarkable agreement.

During the 142-year study period, the sea surface temperature dropped only one-tenth of one degree, but it was enough to cause arid conditions in North America and Europe.

The Anastazi people-who lived in dramatic cliff dwellings near what later became known as the “Four Corners” area at the intersection of the state of Utah, Colorado, New Mexico, and Arizona-left their settlements at Mesa Verde and other locations some 600 years ago without explanation. A prolonged drought is thought to be one of the contributing factors to their departure.

In Europe, the study period was preceded by three years of torrential rains, which led to the Great Famine from 1315 to 1320, and marked the transition from the Medieval Warm Period to the Little Ice Age, which began in the mid 1500s. During that time, extreme weather conditions were thought to be responsible for continued localized crop failures and famines throughout Europe during the remainder of the 14th Century.

“The marriage of complex climate models with paleo-records of sea surface temperature and other climate variables provide valuable insight to climate scientists who wish to understand climate variability and change before the instrumental record,” said Burgman.

Warning that the Palmyra Atoll data only represents one data point, Burgman emphasized that he would like to test his thesis with data from other oceans. “If we can fill in the gaps with data from corals and other records from the Atlantic, Pacific, and Indian oceans, we’ll have a better idea of what has happened to the global climate over time,” he added.

In the study, Burgman and his colleagues used the reconstructed tropical Pacific sea surface temperatures to create a 16-member ensemble of atmospheric general circulation model (ACGM) simulations, coupled with a one-layer ocean model outside of the tropical Pacific. When the ACGM simulations were compared with the modern climate simulations, they were able to reproduce many aspects of the medieval climate found in observational records for much of the Western Hemisphere, northern Eurasia, and the northern tropics. These results suggest that many features of global medieval hydroclimate changes can be explained by tropical Pacific sea surface temperatures.

The Earth and moon formed later than previously thought

The Earth and Moon were created as the result of a giant collision between two planets the size of Mars and Venus. Until now it was thought to have happened when the solar system was 30 million years old or approx. 4,537 million years ago. But new research from the Niels Bohr Institute shows that the Earth and Moon must have formed much later – perhaps up to 150 million years after the formation of the solar system. The research results have been published in the scientific journal, Earth and Planetary Science Letters.

“We have determined the ages of the Earth and the Moon using tungsten isotopes, which can reveal whether the iron cores and their stone surfaces have been mixed together during the collision”, explains Tais W. Dahl, who did the research as his thesis project in geophysics at the Niels Bohr Institute at the University of Copenhagen in collaboration with professor David J. Stevenson from the California Institute of Technology (Caltech).

Turbulent collisions

The planets in the solar system were created by collisions between small dwarf planets orbiting the newborn sun. In the collisions the small planets melted together and formed larger and larger planets. The Earth and Moon are the result of a gigantic collision between two planets the size of Mars and Venus. The two planets collided at a time when both had a core of metal (iron) and a surrounding mantle of silicates (rock). But when did it happen and how did it happen? The collision took place in less than 24 hours and the temperature of the Earth was so high (7000º C), that both rock and metal must have melted in the turbulent collision. But were the stone mass and iron mass also mixed together?

Until recently it was believed that the rock and iron mixed completely during the planet formation and so the conclusion was that the Moon was formed when the solar system was 30 million years old or approximately 4,537 million years ago. But new research shows something completely different.

Dating with radioactive elements

The age of the Earth and Moon can be dated by examining the presence of certain elements in the Earth’s mantle. Hafnium-182 is a radioactive substance, which decays and is converted into the isotope tungsten-182. The two elements have markedly different chemical properties and while the tungsten isotopes prefer to bond with metal, hafnium prefers to bond to silicates, i.e. rock.

It takes 50-60 million years for all hafnium to decay and be converted into tungsten, and during the Moon forming collision nearly all the metal sank into the Earth’s core. But did all the tungsten go into the core?

“We have studied to what degree metal and rock mix together during the planet forming collisions. Using dynamic model calculations of the turbulent mixing of the liquid rock and iron masses we have found that tungsten isotopes from the Earth’s early formation remain in the rocky mantle”, explains Tais W. Dahl, Niels Bohr Institute at the University of Copenhagen.

The new studies imply that the moon forming collision occurred after all of the hafnium had decayed completely into tungsten.

“Our results show that metal core and rock are unable to emulsify in these collisions between planets that are greater than 10 kilometres in diameter and therefore that most of the Earth’s iron core (80-99 %) did not remove tungsten from the rocky material in the mantle during formation”, explains Tais W. Dahl.

The result of the research means that the Earth and the Moon must have been formed much later than previously thought – that is to say not 30 million years after the formation of the solar system 4,567 million years ago but perhaps up to 150 million years after the formation of the solar system.

Some like it hot: Site of human evolution was scorching

If you think summer in your hometown is hot, consider it fortunate that you don’t live in the Turkana Basin of Kenya, where the average daily temperature has reached the mid-90s or higher, year-round, for the past 4 million years.

The need to stay cool in that cradle of human evolution may relate, at least in part, to why pre-humans learned to walk upright, lost the fur that covered the bodies of their predecessors and became able to sweat more, Johns Hopkins University earth scientist Benjamin Passey said.

“The ‘take home’ message of our study,” said Passey, whose report appears this week in the online early edition of Proceedings of the National Academy of Sciences, “is that this region, which is one of the key places where fossils have been found documenting human evolution, has been a really hot place for a really long time, even during the period between 3 million years ago and now when the ice ages began and the global climate became cooler.”

Passey, an assistant professor in the Morton K. Blaustein Department of Earth and Planetary Sciences at the university’s Zanvyl Krieger School of Arts and Sciences, says that conclusion lends support to the so-called “thermal hypothesis” of human evolution.

That hypothesis states that our pre-human ancestors gained an evolutionary advantage in walking upright because doing so was cooler (when it is sunny, the near-surface air is warmer than air a few feet above the ground) and exposed their body mass to less sunlight than did crawling on all fours. The loss of body hair (fur) and the ability to regulate body temperature through perspiration would have been other adaptations helpful for living in a warm climate, according to the hypothesis.

“In order to figure out if (the thermal hypothesis) is possibly true or not, we have to know whether it was actually hot when and where these beings were evolving,” he said. “If it was hot, then that hypothesis is credible. If it was not, then we can throw out the hypothesis.”

Evaluating whether the ancient Turkana Basin climate was, in fact, the same scorching place it is today has been difficult up until now because there are very few direct ways of determining ancient temperature. Efforts to get a handle on temperatures 4 million years ago through analysis of fossil pollen, wood and mammals were only somewhat successful, as they reveal more about plants and rainfall and less about temperature, Passey said.

Passey, however, previously was part of a team at the California Institute of Technology that developed a geochemical approach to the “temperature problem.” The method involves determining the temperatures of carbonate minerals that form naturally in soil (including a sedimentary rock called “caliche” and hard pan, which is a dense layer of soil, usually found below the uppermost topsoil layer) by examining “clumps” of rare isotopes. (Isotopes are atoms of the same element that have different masses due to differences in the number of neutrons they contain.)

In the case of soil carbonates common in the Turkana Basin, the amount of rare carbon-13 bonded directly to rare oxygen-18 provides a record of the temperature during the initial formation of the mineral. It told the team that soil carbonates there formed at average soil temperatures between 86 and 95 degrees Fahrenheit, leading to the conclusion that average daytime air temperatures were even higher. In other words, it was hot way back then in what is now northeastern Kenya.

“We already have evidence that habitats in ancient East Africa were becoming more open, which is also hypothetically part of the scenario for the development of bipedalism and other human evolution, but now we have evidence that it was hot,” Passey said. “Thus, we can say that the ‘thermal hypothesis’ is credible.”

Early Earth haze likely provided ultraviolet shield for planet

A new study by CU-Boulder researchers indicates a thick organic haze shrouding Earth several billion years ago was similar to the one now hovering over Saturn's largest moon, Titan (above) and may have protected primordial life on the planet from damaging ultraviolet radiation. -  Image courtesy NASA/JPL/Space Science Institute.
A new study by CU-Boulder researchers indicates a thick organic haze shrouding Earth several billion years ago was similar to the one now hovering over Saturn’s largest moon, Titan (above) and may have protected primordial life on the planet from damaging ultraviolet radiation. – Image courtesy NASA/JPL/Space Science Institute.

A new study shows a thick organic haze that enshrouded early Earth several billion years ago may have been similar to the haze now hovering above Saturn’s largest moon, Titan, and would have protected primordial life on the planet from the damaging effects of ultraviolet radiation.

The University of Colorado at Boulder scientists believe the haze was made up primarily of methane and nitrogen chemical byproducts created by reactions with light, said CU-Boulder doctoral student Eric Wolf, lead study author. Not only would the haze have shielded early Earth from UV light, it would have allowed gases like ammonia to build up, causing greenhouse warming and perhaps helped to prevent the planet from freezing over.

The researchers determined the haze of hydrocarbon aerosols was probably made up of fluffy, microscopic particles shaped somewhat like cottonwood tree seeds that would have blocked UV but allowed visible light through to Earth’s surface, Wolf said.

Prior to the new study, the prevailing scientific view was that the atmosphere of Earth some 3 billion years ago was primarily made up of nitrogen gas with lesser amounts of carbon dioxide, methane, hydrogen and water vapor, said Wolf. “Since climate models show early Earth could not have been warmed by atmospheric carbon dioxide alone because of its low levels, other greenhouse gases must have been involved. We think the most logical explanation is methane, which may have been pumped into the atmosphere by early life that was metabolizing it.”

A paper on the subject by Wolf and CU-Boulder Professor Brian Toon of the atmospheric and oceanic sciences department is being published in the June 4 issue of Science. NASA’s Planetary Atmosphere Program funded the study.

The output of the sun during the Archean period some 3.8 billion to 2.5 billion years ago is thought to have been 20 percent to 30 percent fainter than today, said Wolf. But previous work by other scientists produced geological and biological evidence that indicates Earth’s surface temperatures were as warm or warmer than today.

As part of the early Earth study, Wolf and Toon used a climate model from the National Center for Atmospheric Research and concepts from lab studies by another CU group led by chemistry and biochemistry Professor Margaret Tolbert that help explain the odd haze of Titan, the second largest moon in the solar system and the largest moon of Saturn. Titan came under intense study following the arrival of the Cassini spacecraft at Saturn in 2004, allowing scientists to determine it was the only moon in the solar system with both a dense atmosphere and liquid on its surface.

Previous modeling efforts of early Earth haze by other scientists assumed that aerosol particulates making up the haze were spherical, said Wolf. But the spherical shape does not adequately account for the optical properties of the haze that blanketed the planet.

Lab simulations helped researchers conclude that the Earth haze likely was made up of irregular “chains” of aggregate particles with greater geometrical sizes than spheres, similar to the shape of aerosols believed to populate Titan’s thick atmosphere. Wolf said the aggregate aerosol particulates are believed to be fragmented geometric shapes known as fractals that can be split into parts.

During the Archean period there was no ozone layer in Earth’s atmosphere to protect life on the planet, said Wolf. “The UV shielding methane haze over early Earth we are suggesting not only would have protected Earth’s surface, it would have protected the atmospheric gases below it — including the powerful greenhouse gas, ammonia — that would have played a significant role in keeping the early Earth warm.”

CU-Boulder researchers estimated there were roughly 100 million tons of haze produced annually in the atmosphere of early Earth during the Archean. “If this was the case, an early Earth atmosphere literally would have been dripping organic material into the oceans, providing manna from heaven for the earliest life to sustain itself,” Toon said.

“Methane is the key to make this climate model run, so one of our goals now is to pin down where and how it originated,” said Toon. If Earth’s earliest organisms didn’t produce the methane, it may have been generated by the release of gasses during volcanic eruptions either before or after life first arose — a hypothesis that will requires further study, he said.

The new CU-Boulder study will likely re-ignite interest in a controversial experiment by scientists Stanley Miller and Harold Urey in the 1950s in which methane, ammonia, nitrogen and water were combined in a test tube. After Miller and Urey ran an electrical current through the mixture to simulate the effects of lightning or powerful UV radiation, the result was the creation of a small pool of amino acids — the building blocks of life.

Toon said the theory of early Earth being shrouded by a gaseous blanket containing methane and ammonia first arose in the 1960s and was subsequently discarded by scientists. In the 1970s and 1980s some scientists suggested the early Earth atmosphere was similar to those on Mars and Venus with lots of carbon dioxide, another theory that eventually went by the wayside. Since CO2-rich atmospheres do not produce organic molecules easily, scientists began looking in deep-sea volcanic vents and at wayward asteroids to explain early Earth life.

A 1997 paper by the late Carl Sagan of Cornell University and Christopher Chyba, then at the University of Arizona, proposed that an organic aerosol shield in early Earth’s atmosphere would have protected the ammonia wafting beneath it, allowing heating to occur at Earth’s surface. But the authors proposed the haze particles were spherical rather than irregular aggregate particles Wolf and Toon suggest and did not consider methane to be the driver of the system, eventually sinking that theory.

“We still have a lot of research to do in order to refine our new view of early Earth,” said Wolf. “But we think this paper solves a number of problems associated with the haze that existed over early Earth and likely played a role in triggering or at least supporting the earliest life on the planet.”

From space, early Earth probably looked much like Titan looks today, said Toon. “It would have been shrouded by a reddish haze that would have been difficult to see through, and the ocean probably was a greenish color caused by dissolved iron in the oceans. It wasn’t a blue planet by any means.”