Reconciling predictions of climate change

Harvard University researchers have resolved a conflict in estimates of how much the Earth will warm in response to a doubling of carbon dioxide in the atmosphere.

That conflict - between temperature ranges based on global climate models and paleoclimate records and ranges generated from historical observations - prevented the United Nations' Intergovernmental Panel on Climate Change (IPCC) from providing a best estimate in its most recent report for how much the Earth will warm as a result of a doubling of CO2 emissions.

The researchers found that the low range of temperature increase - between 1 and 3 degrees Celsius - offered by the historical observations did not take into account long-term warming patterns. When these patterns are taken into account, the researchers found that not only do temperatures fall within the canonical range of 1.5 to 4.5 degrees Celsius but that even higher ranges, perhaps up to 6 degrees, may also be possible.

The research is published in Science Advances.

CO2 in Earth's atmosphere if half of global-warming emissions are not absorbed (NASA simulation). By NASA/GSFC [Public domain], via Wikimedia Commons

It's well documented that different parts of the planet warm at different speeds. The land over the northern hemisphere, for example, warms significantly faster than water in the Southern Ocean.

"The historical pattern of warming is that most of the warming has occurred over land, in particular over the northern hemisphere," said Cristian Proistosescu, PhD '17, and first author of the paper. "This pattern of warming is known as the fast mode - you put CO2 in the atmosphere and very quickly after that, the land in the northern hemisphere is going to warm."

But there is also a slow mode of warming, which can take centuries to realize. That warming, which is most associated with the Southern Ocean and the Eastern Equatorial Pacific, comes with positive feedback loops that amplify the process. For example, as the oceans warm, cloud cover decreases and a white reflecting surface is replaced with a dark absorbent surface.

The researchers developed a mathematical model to parse the two different modes within different climate models.

"The models simulate a warming pattern like today's, but indicate that strong feedbacks kick in when the Southern Ocean and Eastern Equatorial Pacific eventually warm, leading to higher overall temperatures than would simply be extrapolated from the warming seen to date," said Peter Huybers, Professor of Earth and Planetary Sciences and of Environmental Science and Engineering at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) and co-author of the paper.

Huybers and Proistosescu found that while the slow mode of warming contributes a great deal to the ultimate amount of global warming, it is barely present in present-day warming patterns. "Historical observations give us a lot of insight into how climate changes and are an important test of our climate models," said Huybers, "but there is no perfect analogue for the changes that are coming."

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Tipping points are real: Gradual changes in CO2 levels can induce abrupt climate changes

During the last glacial period, within only a few decades the influence of atmospheric CO2 on the North Atlantic circulation resulted in temperature increases of up to 10 degrees Celsius in Greenland - as indicated by new climate calculations from researchers at the Alfred Wegener Institute and the University of Cardiff. Their study is the first to confirm that there have been situations in our planet's history in which gradually rising CO2 concentrations have set off abrupt changes in ocean circulation and climate at "tipping points." These sudden changes, referred to as Dansgaard-Oeschger events, have been observed in ice cores collected in Greenland. The results of the study have just been released in the journal Nature Geoscience.

Ice core sample taken from drill. Photo by Lonnie Thompson, Byrd Polar Research Center, Ohio State University. [Public domain], via Wikimedia Commons

Previous glacial periods were characterised by several abrupt climate changes in the high latitudes of the Northern Hemisphere. However, the cause of these past phenomena remains unclear. In an attempt to better grasp the role of CO2 in this context, scientists from the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) recently conducted a series of experiments using a coupled atmosphere-ocean-sea ice model.

First author Xu Zhang explains: "With this study, we've managed to show for the first time how gradual increases of CO2 triggered rapid warming." This temperature rise is the result of interactions between ocean currents and the atmosphere, which the scientists used the climate model to explore. According to their findings, the increased CO2 intensifies the trade winds over Central America, as the eastern Pacific is warmed more than the western Atlantic. This is turn produces increased moisture transport from the Atlantic, and with it, an increase in the salinity and density of the surface water. Finally, these changes lead to an abrupt amplification of the large-scale overturning circulation in the Atlantic. "Our simulations indicate that even small changes in the CO2 concentration suffice to change the circulation pattern, which can end in sudden temperature increases," says Zhang.

Further, the study's authors reveal that rising CO2 levels are the dominant cause of changed ocean currents during the transitions between glacial and interglacial periods. As climate researcher Gerrit Lohmann explains, "We can't say for certain whether rising CO2 levels will produce similar effects in the future, because the framework conditions today differ from those in a glacial period. That being said, we've now confirmed that there have definitely been abrupt climate changes in the Earth's past that were the result of continually rising CO2 concentrations."

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Methane muted: How did early Earth stay warm?

For at least a billion years of the distant past, planet Earth should have been frozen over but wasn't. Scientists thought they knew why, but a new modeling study from the Alternative Earths team of the NASA Astrobiology Institute has fired the lead actor in that long-accepted scenario.

Humans worry about greenhouse gases, but between 1.8 billion and 800 million years ago, microscopic ocean dwellers really needed them. The sun was 10 to 15 percent dimmer than it is today - too weak to warm the planet on its own. Earth required a potent mix of heat-trapping gases to keep the oceans liquid and livable.

For decades, atmospheric scientists cast methane in the leading role. The thinking was that methane, with 34 times the heat-trapping capacity of carbon dioxide, could have reigned supreme for most of the first 3.5 billion years of Earth history, when oxygen was absent initially and little more than a whiff later on. (Nowadays oxygen is one-fifth of the air we breathe, and it destroys methane in a matter of years.)

Full structural formula of the methane molecule

"A proper accounting of biogeochemical cycles in the oceans reveals that methane has a much more powerful foe than oxygen," said Stephanie Olson, a graduate student at the University of California, Riverside, a member of the Alternative Earths team and lead author of the new study published September 26 in the Proceedings of the National Academy of Sciences. "You can't get significant methane out of the ocean once there is sulfate."

Sulfate wasn't a factor until oxygen appeared in the atmosphere and triggered oxidative weathering of rocks on land. The breakdown of minerals such as pyrite produces sulfate, which then flows down rivers to the oceans. Less oxygen means less sulfate, but even 1 percent of the modern abundance is sufficient to kill methane, Olson said.

Olson and her Alternative Earths coauthors, Chris Reinhard, an assistant professor of earth and atmospheric sciences at Georgia Tech University, and Timothy Lyons, a distinguished professor of biogeochemistry at UC Riverside, assert that during the billion years they assessed, sulfate in the ocean limited atmospheric methane to only 1 to 10 parts per million - a tiny fraction of the copious 300 parts per million touted by some previous models.

The fatal flaw of those past climate models and their predictions for atmospheric composition, Olson said, is that they ignore what happens in the oceans, where most methane originates as specialized bacteria decompose organic matter.

Seawater sulfate is a problem for methane in two ways: Sulfate destroys methane directly, which limits how much of the gas can escape the oceans and accumulate in the atmosphere. Sulfate also limits the production of methane. Life can extract more energy by reducing sulfate than it can by making methane, so sulfate consumption dominates over methane production in nearly all marine environments.

The numerical model used in this study calculated sulfate reduction, methane production, and a broad array of other biogeochemical cycles in the ocean for the billion years between 1.8 billion and 800 million years ago. This model, which divides the ocean into nearly 15,000 three-dimensional regions and calculates the cycles for each region, is by far the highest resolution model ever applied to the ancient Earth. By comparison, other biogeochemical models divide the entire ocean into a two-dimensional grid of no more than five regions.

"Free oxygen [O2] in the atmosphere is required to form a protective layer of ozone [O3], which can shield methane from photochemical destruction," Reinhard said. When the researchers ran their model with the lower oxygen estimates, the ozone shield never formed, leaving the modest puffs of methane that escaped the oceans at the mercy of destructive photochemistry.

With methane demoted, scientists face a serious new challenge to determine the greenhouse cocktail that explains our planet's climate and life story, including a billion years devoid of glaciers, Lyons said. Knowing the right combination other warming agents, such as water vapor, nitrous oxide, and carbon dioxide, will also help us assess habitability of the hundreds of billions of other Earth-like planets estimated to reside in our galaxy.

"If we detect methane on an exoplanet, it is one of our best candidates as a biosignature, and methane dominates many conversations in the search for life on Mars," Lyons said. "Yet methane almost certainly would not have been detected by an alien civilization looking at our planet a billion years ago - despite the likelihood of its biological production over most of Earth history."

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Researchers reduce climate-warming CO2 to building blocks for fuels

Turning carbon dioxide into stored energy sounds like science fiction: researchers have long tried to find simple ways to convert this greenhouse gas into fuels and other useful chemicals. Now, a group of researchers led by Professor Ted Sargent of the University of Toronto's Faculty of Applied Science & Engineering have found a more efficient way, through the wonders of nanoengineering.

Drs. Min Liu and Yuanjie Pang, along with a team of graduate students and post-doctoral fellows in University of Toronto Engineering, have developed a technique powered by renewable energies such as solar or wind. The catalyst takes climate-warming carbon-dioxide (CO2) and converts it to carbon-monoxide (CO), a useful building block for carbon-based chemical fuels, such as methanol, ethanol and diesel.

The frozen version of CO2, small pellets of dry ice sublimating in air. By Richard Wheeler (Zephyris) at en.wikipedia (Transferred from en.wikipedia) [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0/)], via Wikimedia Commons

"CO2 reduction is an important challenge due to inertness of the molecule," says Liu. "We were looking for the best way to both address mounting global energy needs and help the environment," adds Pang. "If we take CO2 from industrial flue emissions or from the atmosphere, and use it as a reagent for fuels, which provide long-term storage for green energy, we're killing two birds with one stone."

The team's solution is sharp: they start by fabricating extremely small gold "nanoneedles" - the tip of each needle is 10,000 times smaller than a human hair. "The nanoneedles act like lightning rods for catalyzing the reaction," says Liu.

When they applied a small electrical bias to the array of nanoneedles, they produced a high electric field at the sharp tips of the needles. This helps attract CO2, speeding up the reduction to CO, with a rate faster than any catalyst previously reported. This represents a breakthrough in selectivity and efficiency which brings CO2 reduction closer to the realm of commercial electrolysers. The team is now working on the next step: skipping the CO and producing more conventional fuels directly.

Their work is published in the journal Nature.

"The field of water-splitting for energy storage has seen rapid advances, especially in the intensity with which these reactions can be performed on a heterogeneous catalyst at low overpotential - now, analogous breakthroughs in the rate of CO2 reduction using renewable electricity are urgently needed," says Michael Graetzel, a professor of physical chemistry at École Polytechnique Fédérale de Lausanne and a world leader in this field. "The University of Toronto team's breakthrough was achieved using a new concept of field-induced reagent concentration."

"Solving global energy challenges needs solutions that cut across many fields," says Sargent. "This work not only provides a new solution to a longstanding problem of CO2 reduction, but opens possibilities for storage of alternative energies such as solar and wind."

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Unexpected information about Earth's climate history from Yellow River sediment

By meticulously examining sediments in China's Yellow River, a Swedish-Chinese research group are showing that the history of tectonic and climate evolution on Earth may need to be rewritten. 

Their findings are published today in the highly reputed journal Nature Communications.

To reconstruct how the global climate and topography of the Earth's surface have developed over millions of years, deposits of eroded land sediment transported by rivers to ocean depths are often used. This process is assumed to have been rapid and, by the same token, not to have resulted in any major storages of this sediment as large deposits along the way.

However, knowledge gaps and contradictory data in research to date are impeding an understanding of climate and landscape history. In an attempt to fill the gaps and reconcile the contradictions, the researchers have been investigating present-day and ancient sediment deposits in the world's most sediment-rich river: the Yellow River in China.

The researchers, from Uppsala University (led by Dr. Thomas Stevens) and Lanzhou University (led by Dr. Junsheng Nie), China, analysed Yellow River sediment from source to sink and determined its mineral composition. They also determined the age of mineral grains of zircon, a very hard silicate mineral that is highly resistant to weathering.

Zircon ages serve as a unique fingerprint that yields information about the sources of these sediment residues from mountain chains, according to Thomas Stevens of Uppsala University's Department of Earth Sciences, one of the principal authors of the study.

The Yellow River is believed to gain most of its sediment from wind-blown mineral dust deposits called loess, concentrated on the Chinese Loess Plateau. This plateau is the largest and one of the most important past climate archives on land, and also records past atmospheric dust activity: a major driver of climate change.

The scientists found that the composition of sediment from the Yellow River underwent radical change after passing the Chinese Loess Plateau. Contrary to their expectations, however, the windborne loess was not the main source of the sediment. Instead, they found that the Loess Plateau acts as a sink for Yellow River material eroded from the uplifting Tibetan plateau.

This finding completely changes our understanding of the origin of the Chinese Loess Plateau. It also demonstrates large scale sediment storage on land, which explains the previously contradictory findings in this area.

'Our results suggest that a major change in the monsoon around 3.6 million years ago caused the onset of Yellow River drainage, accelerated erosion of the Tibetan plateau and drove loess deposition,' Thomas Stevens writes.

Weathering of this eroded material also constitutes a further mechanism that may explain the reduced levels of atmospheric carbon dioxide at the beginning of the Ice Age. The researchers' next step will be to compare terrestrial and marine records of erosion to gauge how far sediment storage on land has impacted the marine record.

'Only then will we be able to assess the true rates of erosion and its effect on atmospheric CO2 and thus the climate in geologic time,' says Stevens.

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What happened to early Mars' atmosphere? New study eliminates one theory

Scientists may be closer to solving the mystery of how Mars changed from a world with surface water billions of years ago to the arid Red Planet of today.

A new analysis of the largest known deposit of carbonate minerals on Mars suggests that the original Martian atmosphere may have already lost most of its carbon dioxide by the era of valley network formation.

"The biggest carbonate deposit on Mars has, at most, twice as much carbon in it as the current Mars atmosphere," said Bethany Ehlmann of the California Institute of Technology and NASA Jet Propulsion Laboratory, both in Pasadena. "Even if you combined all known carbon reservoirs together, it is still nowhere near enough to sequester the thick atmosphere that has been proposed for the time when there were rivers flowing on the Martian surface."

Carbon dioxide makes up most of the Martian atmosphere. That gas can be pulled out of the air and sequestered or pulled into the ground by chemical reactions with rocks to form carbonate minerals. Years before the series of successful Mars missions, many scientists expected to find large Martian deposits of carbonates holding much of the carbon from the planet's original atmosphere. Instead, these missions have found low concentrations of carbonate distributed widely, and only a few concentrated deposits. By far the largest known carbonate-rich deposit on Mars covers an area at least the size of Delaware, and maybe as large as Arizona, in a region called Nili Fossae.

Christopher Edwards, a former Caltech researcher now with the U.S. Geological Survey in Flagstaff, Arizona, and Ehlmann reported the findings and analysis in a paper posted online by the journal Geology. Their estimate of how much carbon is locked into the Nili Fossae carbonate deposit uses observations from numerous Mars missions, including the Thermal Emission Spectrometer (TES) on NASA's Mars Global Surveyor orbiter, the mineral-mapping Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) and two telescopic cameras on NASA's Mars Reconnaissance Orbiter, and the Thermal Emission Imaging System (THEMIS) on NASA's Mars Odyssey orbiter.

Edwards and Ehlmann compare their tally of sequestered carbon at Nili Fossae to what would be needed to account for an early Mars atmosphere dense enough to sustain surface waters during the period when flowing rivers left their mark by cutting extensive river-valley networks. By their estimate, it would require more than 35 carbonate deposits the size of the one examined at Nili Fossae. They deem it unlikely that so many large deposits have been overlooked in numerous detailed orbiter surveys of the planet. While deposits from an even earlier time in Mars history could be deeper and better hidden, they don't help solve the thin-atmosphere conundrum at the time the river-cut valleys formed.

The modern Martian atmosphere is too tenuous for liquid water to persist on the surface. A denser atmosphere on ancient Mars could have kept water from immediately evaporating. It could also have allowed parts of the planet to be warm enough to keep liquid water from freezing. But if the atmosphere was once thicker, what happened to it? One possible explanation is that Mars did have a much denser atmosphere during its flowing-rivers period, and then lost most of it to outer space from the top of the atmosphere, rather than by sequestration in minerals.

"Maybe the atmosphere wasn't so thick by the time of valley network formation," Edwards said. "Instead of Mars that was wet and warm, maybe it was cold and wet with an atmosphere that had already thinned. How warm would it need to have been for the valleys to form? Not very. In most locations, you could have had snow and ice instead of rain. You just have to nudge above the freezing point to get water to thaw and flow occasionally, and that doesn't require very much atmosphere."

NASA's Curiosity Mars rover mission has found evidence of ancient top-of-atmosphere loss, based on the modern Mars atmosphere's ratio of heavier carbon to lighter carbon. Uncertainty remains about how much of that loss occurred before the period of valley formation; much may have happened earlier. NASA's MAVEN orbiter, examining the outer atmosphere of Mars since late 2014, may help reduce that uncertainty.

Arizona State University, Tempe, provided the TES and THEMIS instruments. The Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland., provided CRISM. JPL, a division of Caltech, manages the Mars Reconnaissance Orbiter and Mars Odyssey project for NASA's Science Mission Directorate, Washington, and managed the Mars Global Surveyor project through its nine years of orbiter operations at Mars. Lockheed Martin Space Systems in Denver built the three orbiters.

For more information about the Mars Reconnaissance Orbiter mission, visit:

http://mars.nasa.gov/mro

For more information about the Mars Odyssey mission, visit:

http://mars.nasa.gov/odyssey

Story Source:

The above post is reprinted from materials provided by NASA/Jet Propulsion Laboratory. Note: Materials may be edited for content and length.

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Volcanic rocks resembling Roman concrete explain record uplift in Italian caldera

The discovery of a fiber-reinforced, concrete-like rock formed in the depths of a dormant supervolcano could help explain the unusual ground swelling that led to the evacuation of an Italian port city and inspire durable building materials in the future, Stanford scientists say.

The "natural concrete" at the Campi Flegrei volcano is similar to Roman concrete, a legendary compound invented by the Romans and used to construct the Pantheon, the Coliseum, and ancient shipping ports throughout the Mediterranean.

"This implies the existence of a natural process in the subsurface of Campi Flegrei that is similar to the one that is used to produce concrete," said Tiziana Vanorio, an experimental geophysicist at Stanford's School of Earth, Energy & Environmental Sciences.

Campi Flegrei lies at the center of a large depression, or caldera, that is pockmarked by craters formed during past eruptions, the last of which occurred nearly 500 years ago. Nestled within this caldera is the colorful port city of Pozzuoli, which was founded in 600 B.C. by the Greeks and called "Puteoli" by the Romans.

Beginning in 1982, the ground beneath Pozzuoli began rising at an alarming rate. Within a two-year span, the uplift exceeded six feet-an amount unprecedented anywhere in the world. "The rising sea bottom rendered the Bay of Pozzuoli too shallow for large craft," Vanorio said.

Making matters worse, the ground swelling was accompanied by swarms of micro-earthquakes. Many of the tremors were too small to be felt, but when a magnitude 4 quake juddered Pozzuoli, officials evacuated the city's historic downtown. Pozzuoli became a ghost town overnight.

A teenager at the time, Vanorio was among the approximately 40,000 residents forced to flee Pozzuoli and settle in towns scattered between Naples and Rome. The event made an impression on the young Vanorio, and inspired her interests in the geosciences. Now an assistant professor at Stanford, Vanorio decided to apply her knowledge about how rocks in the deep Earth respond to mechanical and chemical changes to investigate how the ground beneath Pozzuoli was able to withstand so much warping before cracking and setting off micro-earthquakes.

"Ground swelling occurs at other calderas such as Yellowstone or Long Valley in the United States, but never to this degree, and it usually requires far less uplift to trigger earthquakes at other places," Vanorio said. "At Campi Flegrei, the micro-earthquakes were delayed by months despite really large ground deformations."

To understand why the surface of the caldera was able to accommodate incredible strain without suddenly cracking, Vanorio and a post-doctoral associate, Waruntorn Kanitpanyacharoen, studied rock cores from the region. In the early 1980s, a deep drilling program probed the active geothermal system of Campi Flegrei to a depth of about 2 miles. When the pair analyzed the rock samples, they discovered that Campi Flegrei's caprock-a hard rock layer located near the caldera's surface-is rich in pozzolana, or volcanic ash from the region.

The scientists also noticed that the caprock contained tobermorite and ettringite-fibrous minerals that are also found in humanmade concrete. These minerals would have made Campi Flegrei's caprock more ductile, and their presence explains why the ground beneath Pozzuoli was able to withstand significant bending before breaking and shearing. But how did tobermorite and ettringite come to form in the caprock?

Once again, the drill cores provided the crucial clue. The samples showed that the deep basement of the caldera-the "wall" of the bowl-like depression-consisted of carbonate-bearing rocks similar to limestone, and that interspersed within the carbonate rocks was a needle-shaped mineral called actinolite.

"The actinolite was the key to understanding all of the other chemical reactions that had to take place to form the natural cement at Campi Flegrei," said Kanitpanyacharoen, who is now at Chulalongkorn University in Thailand.

From the actinolite and graphite, the scientists deduced that a chemical reaction called decarbonation was occurring beneath Campi Flegrei. They believe that the combination of heat and circulating mineral-rich waters decarbonates the deep basement, prompting the formation of actinolite as well as carbon dioxide gas. 

As the CO2 mixes with calcium-carbonate and hydrogen in the basement rocks, it triggers a chemical cascade that produces several compounds, one of which is calcium hydroxide. Calcium hydroxide, also known as portlandite or hydrated lime, is one of the two key ingredients in humanmade concrete, including Roman concrete. Circulating geothermal fluids transport this naturally occurring lime up to shallower depths, where it combines with the pozzolana ash in the caprock to form an impenetrable, concrete-like rock capable of withstanding very strong forces.

"This is the same chemical reaction that the ancient Romans unwittingly exploited to create their famous concrete, but in Campi Flegrei it happens naturally," Vanorio said.

In fact, Vanorio suspects that the inspiration for Roman concrete came from observing interactions between the volcanic ash at Pozzuoli and seawater in the region. The Roman philosopher Seneca, for example, noted that the "dust at Puteoli becomes stone if it touches water."

"The Romans were keen observers of the natural world and fine empiricists," Vanorio said. "Seneca, and before him Vitruvius, understood that there was something special about the ash at Pozzuoli, and the Romans used the pozzolana to create their own concrete, albeit with a different source of lime."

Pozzuoli was the main commercial and military port for the Roman Empire, and it was common for ships to use pozzolana as ballast while trading grain from the eastern Mediterranean. As a result of this practice, volcanic ash from Campi Flegrei-and the use of Roman concrete-spread across the ancient world. Archeologists have recently found that piers in Alexandria, Caesarea, and Cyprus are all made from Roman concrete and have pozzolana as a primary ingredient.

Interestingly, the same chemical reaction that is responsible for the unique properties of the Campi Flegrei's caprock can also trigger its downfall. If too much decarbonation occurs-as might happen if a large amount of saltwater, or brine, gets injected into the system-an excess of carbon dioxide, methane and steam is produced. As these gases rise toward the surface, they bump up against the natural cement layer, warping the caprock. This is what lifted Pozzuoli in the 1980s. When strain from the pressure buildup exceeded the strength of the caprock, the rock sheared and cracked, setting off swarms of micro-earthquakes. As pent-up gases and fluids vent into the atmosphere, the ground swelling subsided. Vanorio and Kanitpanyacharoen suspect that as more calcium hydroxide was produced at depth and transported to the surface, the damaged caprock was slowly repaired, its cracks "healed" as more natural cement was produced.

Vanorio believes the conditions and processes responsible for the exceptional rock properties at Campi Flegrei could be present at other calderas around the world. A better understanding of the conditions and processes that formed Campi Flegrei's caprock could also allow scientists to recreate it in the lab, and perhaps even improve upon it to engineer more durable and resilient concretes that are better able to withstand large stresses and shaking, or to heal themselves after damage.

"There is a need for eco-friendly materials and concretes that can accommodate stresses more easily," Vanorio said. "For example, extracting natural gas by hydraulic fracturing can cause rapid stress changes that cause concrete well casings to fail and lead to gas leaks and water contamination."

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The Event that Transformed Earth

Up until 2.4 billion years ago, there was no oxygen in the air. It took something big to change that – perhaps the biggest evolutionary leap of all.

If you could build a time machine and go back to Earth's distant past, you'd get a nasty surprise. You wouldn't be able to breathe the air. Unless you had some breathing apparatus, you would asphyxiate within minutes.

The Great Oxidisation Event (Credit: APIX / Alamy)

For the first half of our planet's history, there was no oxygen in the atmosphere. This life-giving gas only started to appear about 2.4 billion years ago.

This "Great Oxidation Event" was one of the most important things to ever happen on this planet. 

Without it, there could never have been any animals that breathe oxygen: no insects, no fish, and certainly no humans.

For decades, scientists have worked to understand how and why the first oxygen was pumped into the air. They have long suspected that life itself was responsible for creating the air that we breathe.

But not just any life. If the latest findings are to be believed, life itself was undergoing a tremendous transformation just before the Great Oxidation Event. This evolutionary leap forward may be the key to understanding what happened.

Earth was already 2 billion years old at the time of the Great Oxidation Event, having formed 4.5 billion years ago. It was inhabited, but only by single-celled organisms.

It's not clear exactly when life began, but the oldest known fossils of these microorganisms date back 3.5 billion years, so it must have been before that. That means life had been around for at least a billion years before the Great Oxidation Event.

Those simple life-forms are the prime suspects for the Great Oxidation Event. One group in particular stands out: cyanobacteria. Today, these microscopic organisms sometimes form bright blue-green layers on ponds and oceans.

Their ancestors invented a trick that has since spread like wildlife. They evolved a way to take energy from sunlight, and use it to make sugars out of water and carbon dioxide.

This is called photosynthesis, and today it's how all green plants get their food. That tree down your street is pretty much using the same chemical process that the first cyanobacteria used billions of years ago.

It was the cyanobacteria, pumping out unwanted oxygen, that transformed Earth's atmosphere

From the bacteria's point of view, photosynthesis has one irritating downside. It produces oxygen as a waste product. Oxygen is of no use to them, so they release it into the air.

So there's a simple explanation for the Great Oxidation Event. It was the cyanobacteria, pumping out unwanted oxygen, that transformed Earth's atmosphere.

But while this explains how it happened, it doesn't explain why, and it certainly doesn't explain when it happened.

The problem is that cyanobacteria seem to have been around long before the Great Oxidation Event. 

"They're probably among the first organisms we have on this planet," says Bettina Schirrmeister of the University of Bristol in the UK.

We can be confident that there were cyanobacteria by 2.9 billion years ago, because there is evidence of isolated "oxygen oases" at that time. They might date as far back as 3.5 billion years, but it's hard to tell because the fossil record is so patchy.

That means the cyanobacteria were busy pumping out oxygen for at least half a billion years before oxygen started appearing in the air. That doesn't make a lot of sense.

One explanation is that there were a lot of chemicals around – perhaps volcanic gases – that reacted with the oxygen, effectively "mopping it up".

But there's another possibility, says Schirrmeister. Maybe the cyanobacteria changed. "Some evolutionary innovation in cyanobacteria helped them to become more successful and more important," she says.

Some modern cyanobacteria have done something that, by bacterial standards, is remarkable. While the vast majority of bacteria are single cells, they are multicellular.

The individual cyanobacterial cells have joined up into stringy filaments, like the carriages of a train. 

That in itself is unusual for bacteria, but some have gone further.

"Many cyanobacteria are able to produce specialised cells that lose their ability to divide," says Schirrmeister. "This is the first form of specialisation we see." It's a simple version of the many specialised cells that animals have, such as muscle, nerve and blood cells.

Schirrmeister thinks multicellularity could have been a game-changer for Earth's early cyanobacteria. It offers several possible advantages.

On the early Earth, single-celled organisms often lived together in flat layers of gunk called "mats". 

Within each mat there would have been many different species of cyanobacteria, and a host of other things to boot.

A multicellular cyanobacterium would have one clear advantage compared to its single-celled rivals. 

It would find it easier to spread, because its larger surface area would mean it was better at attaching itself to slippery rocks. Such an organism would be "less likely to wash away in the current", says Schirrmeister.

Many modern multicellular cyanobacteria can move around within their mats. "They're not extremely fast but they can move," says Schirrmeister. That suggests the primordial ones could as well.

Moving could have helped them survive. At the time the Earth was being bombarded with harmful ultraviolet radiation from the Sun, and there was no ozone layer to keep it out.

"In modern mats, cyanobacteria will turn around and appear vertical instead of horizontal to protect themselves from excess sunlight," says Schirrmeister. "You have also movement between layers. It might be these multicellular cyanobacteria had the ability to position themselves optimally within the mat."

It's a neat idea. But for it to be true, cyanobacteria must have evolved multicellularity before the Great Oxidation Event.

Schirrmeister has spent the last few years trying to figure out when cyanobacteria first evolved multicellularity.

The clues lie in their genes. By examining genes that all cyanobacteria share, and identifying tiny differences between them, Schirrmeister could figure out how they are all related – essentially drawing up a family tree of cyanobacteria.

With that tree in place, Schirrmeister could then home in on the multicellular cyanobacteria, and estimate roughly when they first became multicellular.

Her first attempt, published in 2011, suggested that most modern cyanobacteria are descended from multicellular ancestors. That suggested multicellularity was ancient, but it was difficult to put a firm date on it.

Schirrmeister refined her methods for a second paper, published in 2013. This suggested that multicellularity evolved not long before the Great Oxidation Event, at a time when cyanobacteria were diversifying rapidly.

But that didn't clinch the argument. Her family tree was only based on one gene, albeit a gene shared by every single species of cyanobacterium. That meant the tree was suspect.

So Schirrmeister has now gone one better.

"This time I worked with 756 genes," says Schirrmeister. "The genes I took are present in all cyanobacteria."

Her estimate of the origin of multicellularity is still rough, but it seems to be around 2.5 billion years ago – before the Great Oxidation Event.

There are several different ways to calculate these family trees, and they all gave the same answer. "No matter how we calibrate our phylogeny, it seems more likely we have multicellularity evolving before the Great Oxidation Event," says Schirrmeister.

The results are published in Palaeontology.

This may not be the end of the story. Even if Schirrmeister's results are confirmed, and cyanobacteria did become multicellular just before the Great Oxidation Event, there are two big questions.

The first is, did multicellularity really offer them the advantages she thinks it did? We don't know, but we could find out: by testing how modern single-celled and multicellular cyanobacteria cope with different situations.

The second question is harder: why did it take so long for cyanobacteria to become multicellular? If it is so advantageous, why did they not evolve it sooner, and trigger an earlier Great Oxidation Event?

"The next step is to find out which genes are responsible for multicellularity in cyanobacteria," says Schirrmeister. "Then I could say why did it take that long, why didn't it evolve earlier." If lots of new genes were required, it becomes understandable that it took the cyanobacteria a long time to evolve it.

Whatever caused the Great Oxidation Event, it's clear that it is one of the most important things to ever happen on this planet.

In the short term, it was probably rather bad news for life.

"Oxygen would have been lethal for many bacteria," says Schirrmeister. "It's hard to prove, because from the fossil record we don't have a lot of deposits from that time… [but] we can assume we had a lot of bacteria dying at that point."

But in the longer term, it allowed a whole new kind of life to evolve. Oxygen is a reactive gas – that's why it starts fires – so when some organisms figured out how to harness it, they suddenly had access to a major new source of energy.

By breathing oxygen, organisms could become much more active, and much larger. Moving beyond the simple multicellularity developed by cyanobacteria, some organisms became far more intricate. 

They became plants and animals, from sponges and worms to fish and, ultimately, humans.

If Schirrmeister is right, those first multicellular cyanobacteria triggered the evolution of complex life, including us, by producing oxygen on a global scale. "It made complex life possible," she says.
Not bad for a bunch of tiny blue-green bacteria.

For more information visit:-

http://www.bbc.com/earth/story/20150701-the-origin-of-the-air-we-breathe

http://www.prlabs.co.uk/lab-supplies.php?N=gastube-carbon-dioxide-hr-05-20&Id=11735

When will we find aliens?

For the first time in human history, we have the means to answer the question.

Chris McKay's quest for extraterrestrial life started in 1976, when Viking 1 and 2 landed on Mars. Touching down on Mars for the first time was a big deal, sure, but the then-first-year graduate student was especially excited because the landers found what appeared to be signs of Martian life.

The spacecraft found that something in the dirt - possibly microbes - was taking in nutrients and producing gases like carbon dioxide. But when instruments failed to find any organic molecules, which are the building blocks of any organism, scientists concluded that no, aliens weren't living in the dirt.

To this day, however, scientists like McKay are still baffled by the Viking data, which never conclusively supported the existence of life, but were tantalizing nevertheless. For McKay, now a planetary scientist at NASA Ames Research Center, those results launched a career in astrobiology, despite the warnings of other scientists at the time. "Not only did they tell me not to," he says, "they made fun of me for being interested in it."

Four decades later, he's enjoyed some vindication. As robotic space probes continue to explore the solar system, visiting planets, moons, and asteroids, they're finding watery environments where microbial life could grab hold. Science can actually apply itself to the question instead of it being purely philosophical.

Outside the solar system, astronomers have discovered thousands of worlds - and they estimate our galaxy alone could be filled with hundreds of billions of planets. Many could be similar to Earth, with oceans, an atmosphere, and, yes, life.

In the coming decades, new space probes and telescopes will search for signs of life in the solar system and beyond. "We have a decent chance for finding Earth-like planets and evidence for life by sometime in the early 2030s," says Jim Kasting, a planetary scientist at Penn State University in the US.

Telescopes are used to eavesdrop on distant civilisations

And for the first time in human history, scientists have a plan and the means to answer the question of whether we're alone. "The fact that science can actually apply itself to the question instead of it being purely philosophical is very exciting," says Jason Wright, an astronomer also at Penn State. "It might be a long shot that we can do this, but the question is so compelling."

Undoubtedly, the most exciting kind of alien life would be the intelligent kind: the ETs or the ones depicted in Carl Sagan's novel Contact. Despite Roswell and Area 51, such close encounters have yet to happen. But scientists have been searching for decades, trying to eavesdrop on radio signals from a distant civilisation. Today, for example, the SETI Institute listens with the Allen Telescope Array in California.

Most recently, Wright led a hunt for super-advanced civilisations that have colonised an entire galaxy. In the 1960s, the physicist Freeman Dyson suggested that aliens could power their civilisation using energy from their planet's star. Consuming that energy - to run computers, spaceships, or whatever aliens might need - will radiate heat, like how your laptop gets warm. If such a civilisation took over a galaxy, then you could recognise it by searching for galaxies that radiate more heat than expected.

After scouring through images of 100,000 galaxies taken with the WISE satellite, Wright's team came up with nothing. But that's just for the extreme case of a super-advanced, galaxy-conquering alien. Maybe aliens stayed local. To find out, he says, the next step would be to study the galaxies in more detail, to see if certain regions within each galaxy are producing extra heat. "That would be very unusual," he says. "I don't know how we would go about getting a natural explanation for that."

Still, the search for intelligent life remains a reach. After all, life has flourished on Earth for about 3.5 billion years, and intelligent life (if we consider humans to be intelligent) has been around only for the last 200,000. For most of Earth's history, life consisted of primitive microbes. If we're ever to find life elsewhere, it will probably be microbial. Some could even be in our own cosmic backyard.

One intriguing place to look for life is on Titan, Saturn's largest moon. It's got a thick atmosphere and is the only other place in the solar system covered in seas and lakes - only they're filled with liquid methane, not water. Scientists think liquid is important for life, but the fact that it's methane means any Titanian critters would be fundamentally different from any Earthling.

That doesn't make life impossible, just maybe less probable. Life on Titan would also have to survive frigid temperatures of about -180 degrees C.

For life as we know it, the most important ingredient is still liquid water. And spacecraft are discovering the solar system to be quite wet. In March, observations with the Hubble Space Telescope suggested that an ocean lurks beneath the surface of Jupiter's largest moon, Ganymede. Right now, the Dawn spacecraft is orbiting Ceres, a dwarf planet in the asteroid belt that's 40 percent water by volume, including a possible subsurface ocean.

Among the most promising abodes for life are Mars, Saturn's moon Enceladus, and Jupiter's moon Europa. On Mars, the best chance for life might have been in the past, when the planet was warm and filled with rivers and lakes. Today, Mars is barren and likely inhospitable.

Microbes might, however, be able to eke out an existence below the surface. "I'd say it's 50/50 as to whether there's life on Mars right now," Kasting says. If there is, though, he says it's probably buried as deep as a kilometre underground, where temperatures are warm enough for water to be liquid. Getting there and finding proof, however, might require astronauts drilling on Mars.

Detecting life on Europa might also require drilling. A thick layer of ice maybe several kilometres deep encloses a potentially habitable ocean. Scientists have wanted to go to Europa for years, and they may soon get their chance. The White House's requested budget for 2016 includes $30 million for such a mission. But landing and drilling is difficult and expensive, so if the mission comes to fruition, it will probably study the world from space.

Which is why McKay thinks Enceladus - which also might have a subsurface ocean - is a better bet. "As people realise how difficult Europa is and how inaccessible its ocean is, they're going to be naturally attracted to Enceladus," says McKay, who was part of a team that recently proposed a NASA mission to Enceladus.

The icy moon became a top destination in 2009 when the Cassini spacecraft discovered plumes of water shooting hundreds of kilometres into space. Those plumes, spraying straight from the ocean below, could contain telltale signs of life. "You fly through the plumes from Enceladus," McKay says. "That gives you the best chance of detecting life." No drilling required.

Such an alien-hunting spacecraft would look for two types of molecules: lipids and amino acids. Lipids include fats and oils, and are important for the structure and function of cells. Amino acids are the building blocks of proteins.

The thing about an amino acid is that it can come in two versions that are mirror opposites of each other, like a left and right hand. Of the 20 amino acids that make up life on Earth, 19 are left-handed. Maybe, the thinking goes, amino acids that are biological in origin must generally have the same handedness. Discovering such molecules would certainly suggest life. "That's a grand slam," McKay says.

Still, he admits, that's a fantasy scenario. Microbes might not reveal themselves so easily, or they might not be there at all. Space missions take time and money, so if one spacecraft doesn't find anything, you'd have to wait years for another shot.

Chances might be better outside our solar system, among the billions of other planets in the galaxy. While a mission within the solar system can visit only one place at a time, a space telescope can easily go through dozens or even hundreds of potentially habitable worlds. Instead of lipids and amino acids, such telescopes will look for other molecules: oxygen and other gases that reveal living, breathing aliens.

Building off the resounding success of the Kepler space telescope, which has found thousands of planets, NASA will launch its Transiting Exoplanet Survey Satellite, or TESS, in 2017. Like Kepler, TESS will search for planets that pass in front of their stars, causing a slight dip in starlight. But unlike Kepler, TESS will target planets closer to Earth, and therefore easier to study and detect life.

What's got alien hunters excited is that TESS will find targets for the James Webb Telescope, which, after launching in 2018, will search those planets for atmospheric gases indicative of life.

The idea is this: As a planet passes in front of its star, some of the starlight will penetrate the planet's atmosphere, which appears as a thin outline surrounding the disk of the planet. Depending on its chemical composition, the atmosphere will absorb certain wavelengths of light. By measuring which wavelengths of light get through, astronomers can identify the gases in the atmosphere.

Astronomers have already studied planetary atmospheres with Hubble, showing their methods are sound. With the more powerful JWST, however, they can analyse atmospheres in greater detail.

One of the gases they hope to find is oxygen, which doesn't sit around very long before reacting with other compounds. So to maintain a lot of oxygen in its atmosphere, a planet would need something to replenish it - something living. On Earth, plants and bacteria do the job.

Compared to Mars or even Enceladus, this could be the most likely way scientists find life. "If I was betting today, I would bet on oxygen on an exoplanet," McKay says.

But oxygen is just one gas. Earthlings, for example, produce thousands (just think of all the smells that people, animals, and plants make). Only a handful of them are abundant enough to be detectable from space, however, so astronomers are figuring out which ones could be realistic indicators of life. Some proposed so far include methane and dimethyl sulfide, which phytoplankton produce on Earth.

Of course, finding life won't simply be a matter of detecting gases. Non-living things - such as thermal vents and volcanoes - can spew out many of the same compounds. To determine whether a particular gas is biological in origin, astronomers will have to study the chemistry and the specific properties of the planet.

Even then, short of a message from ET, astronomers may only be able to give the odds for extraterrestrial life. "We won't be sure there's life there, but we may be able to work through all the scenarios and assign a probability," says Sara Seager, an astronomer at MIT.

Another issue is that no one knows what alien life really looks like, so the proposed biosignatures so far are based on Earth's life. "You don't want to be too targeted and only look for stuff like Earth," Wright says. "But you also can't be so general that you have no idea what you're looking for."

To go beyond Earth-based life, Seager wants to identify any and all gases that could be stable and abundant in an atmosphere, regardless of whether anything on Earth makes them. To see if they're viable biosignatures, she will work backwards, reverse engineering biological processes that could produce those gases.

If JWST is to detect life, it will have to get lucky. The telescope was proposed years before astronomers knew the galaxy had billions of planets, so it wasn't designed for planet or alien hunting.

TESS will find thousands of plants, but only some will be good targets for JWST. A suitable planet can't be too small compared to its star. Otherwise, the glare of such a bright star swamps the image, and you can't see the subtle signal from the atmosphere. According to Seager, observing a planet next to its star is like picking out a firefly next to a searchlight from 1,500 kilometres away.

"It's not going to be easy," she says. "We're only going to have a handful of planets to search for signs of life on."

TESS and JWST will also be limited because they can only study planets that pass in front of their stars, which requires a perfect alignment. If JWST fails to find anything, astronomers will have to wait for a specially designed telescope that doesn't rely on transits.

Such a telescope will observe a planet directly, but for that to work, something will have to block the light from the planet's star. One idea called Starshade, which Seager has worked on, is a spacecraft that unfolds like a parasol to block starlight, allowing a separate space telescope to peer into the planet.

The telescope will be able to observe an Earth-sized planet orbiting a sun-like star, something TESS can't do because the brightness of a sun-like star will overwhelm the planet. With more potentially habitable planets - and including truly Earth-like planets - the chances for detecting life improve. "For a direct-imaging telescope, I'd say the odds are pretty good," Kasting says.

If anything, the sheer number and diversity of planets is reason for optimism in the quest for extraterrestrial life. "We know that atmospheres are out there, we've studied many of them, so the possibility is out there for the first time ever," Seager says. "It would be foolish not to take this opportunity."

For more information visit:-

http://www.bbc.com/earth/story/20150429-will-we-find-aliens

http://www.prlabs.co.uk/lab-supplies.php?N=gastube-carbon-dioxide-hr-05-20&Id=11735