Here’s a round-up of recent science headlines we didn’t want you to miss!

Ancient Rivers

Without a smart phone or GPS device, how did early humans find their way out of Africa? A study published last week in PLoS One determines that ancient rivers, now covered by the Sahara Desert, provided habitable routes to follow.

Simulating paleoclimates in the region, the researchers found evidence of three major river systems that likely existed in North Africa 130,000–100,000 years ago, but are now largely buried by dune systems in the desert. When flowing, these rivers likely provided fertile habitats for animals and vegetation, creating “green corridors” across the region.

“It’s exciting to think that 100,000 years ago there were three huge rivers forcing their way across 1000-km of the Sahara desert to the Mediterranean—and that our ancestors could have walked alongside them,” says lead author Tom Coulthard of the University of Hull, UK.

Cosmic Beginnings?

Did life on Earth hail from Mars, as one researcher proposed last month, or comet collisions? Apparently, in both cases, it all has to do with the chemistry. Carl Zimmer, one of our favorite science writers, has a recent New York Times article about the chemistry needed to produce DNA from RNA. And while it doesn’t look like early Earth had those compounds, Mars might have.

Then, earlier this week, a study published in Nature Geoscience finds that the collision of icy comets with planetary bodies could result in the formation of complex amino acids, the building blocks of proteins (and life).

The researchers suggest that this process provides another piece to the puzzle of how life was kick-started on Earth, after a period of time between 4.5 and 3.8 billion years ago when the planet was being bombarded by comets and meteorites.

The team made their discovery by recreating the impact of a comet by firing projectiles through a large high-speed gun. This gun, located at the University of Kent, uses compressed gas to propel projectiles at speeds of 7.15 kilometers per second into targets of ice mixtures, which have a similar composition to comets. The resulting impact created amino acids such as glycine and D- and L-alanine. Sounds like a fun method of discovery…

Speaking of fun collisions, if you want more of them, the Morrison Planetarium at the Academy is featuring Cosmic Collisions in its current show rotation. From the our website:

Creative and destructive, dynamic and dazzling, collisions are a key mechanism in the evolution of the Universe.

Missing Mars Methane

One chemical Mars seems to be missing? Methane. The gas was sought as a possible sign of microbial life currently living on the seemingly barren world. However, despite earlier reports that NASA’s Mars rover, Curiosity, discovered methane on the red planet, NASA reports today in Science that none has been found.

Curiosity’s earlier evidence of methane detection turned out to be within leftover air from Earth. And previous reports of localized methane concentrations up to 45 parts per billion on Mars were based on observations from Earth and from orbit around Mars.

“It would have been exciting to find methane, but we have high confidence in our measurements,” says the report’s lead author, Chris Webster. “We measured repeatedly from Martian spring to late summer, but with no detection of methane.”

But don’t give up on microbial Martians just yet… “This important result will help direct our efforts to examine the possibility of life on Mars,” says NASA’s Michael Meyer. “It reduces the probability of current methane-producing Martian microbes, but this addresses only one type of microbial metabolism. As we know, there are many types of terrestrial microbes that don’t generate methane.”

Looking for extraterrestrial life? Next month’s Brilliant!Science festival can deliver it to you. Visit this page for more information.

Image: the Tunable Laser Spectrometer on-board Curiosity: NASA/JPL-Caltech

When are extreme events part of natural climate variability and when are they due to climate change? It’s important to ask—no matter where you stand on the role of humanity’s impact on the environment.

A group of international scientists decided to address this question, focusing on a dozen or so extreme events from 2012. Their results were published last week in the Bulletin of the American Meteorological Society. (The findings are also available in a downloadable report.)

And the results, were, well, variable.

The researchers did not look at Hurricane Sandy, but they did examine the flooding and the inundation it caused. Because of sea-level rise (a direct result of climate change), the researchers determined that the superstorm did far greater damage than it would have with oceans at normal levels.

The team also determined that heavy rains in the United Kingdom, Japan, and China were not due to global warming, and Australia’s above-average rainfall was due to a La Niña event (or short-term climate variability).

However, a deluge in New Zealand was due to climate change. From Wired:

Total moisture available for this extreme event was 1% to 5% higher as a result of anthropogenic greenhouse gas emissions.

And Arctic sea ice melt? The cap of sea ice covering the North Pole shrunk to its smallest extent last summer. The cause? Climate change.

What about last year’s devastating drought in the Midwest? Scientists judged that climate variability was to blame—not global warming.

However, Stanford researchers did find that the extreme heat that came with last summer’s drought could be attributed to climate change. They also found strong evidence that the high levels of greenhouse gases now in the atmosphere have increased the likelihood of severe heat.

In addition, their findings indicate that extreme weather in the north-central and northeastern United States is more than four times as likely to occur than it was in the pre-industrial era.

The Palo Alto scientists hope the results from these studies can help to quantify the true cost of emissions to society, since the cost of the disaster is measurable.

“Knowing how much our emissions have changed the likelihood of this kind of severe heat event can help us to minimize the impacts of the next heat wave, and to determine the value of avoiding further changes in climate,” says lead author Noah Diffenbaugh, a Stanford associate professor of environmental Earth system science.

Image: Theresa L Wysocki/Flickr

How can you hide a large volcano here on Earth? Place it several miles below the surface of the Pacific Ocean.

Researchers, reporting this week in Nature Geoscience, have discovered just that: a hidden volcano so big it can rival some of the largest in the Solar System. (Think Olympic Mons on Mars.) For several million years, Tamu Massif, has been under cover in the northwest Pacific Ocean, about 1,000 miles east of Japan where three tectonic plates meet: the Pacific, the Farallon and the Izanagi.

Scientists knew there were underwater volcanoes in the Shatsky Rise but it was unclear whether Tamu Massif was a single volcano, or a composite of many eruption points. By integrating several sources of evidence, including core samples and data collected on board the JOIDES Resolution research ship, the authors have confirmed that the mass of basalt that constitutes Tamu Massif did indeed erupt from a single source near the center.

Tamu Massif stands out among underwater volcanoes not just for its size, but also its shape. It is low and broad, meaning that the erupted lava flows must have traveled long distances compared to most other volcanoes on Earth.

Although it rivals Olympic Mons in width and sheer area (about 120,000 square miles), it only rises about 13,000 feet above the sea floor. (Mons is about 14 miles tall! You can thank low martian gravity for that.) Tamu Massif’s tallest point rests at about 6,500 feet below the ocean surface.

“It’s not high, but very wide, so the flank slopes are very gradual,” says lead author William Sager, of the University of Houston. “In fact, if you were standing on its flank, you would have trouble telling which way is downhill. We know that it is a single immense volcano constructed from massive lava flows that emanated from the center of the volcano to form a broad, shield-like shape.”

Thankfully, the massive Tamu Massif is an inactive volcano. Sager and his team put the megavolcano at about 145 million years old, and believe it became inactive within a few million years after it was formed.

“Its shape is different from any other sub-marine volcano found on Earth, and it’s very possible it can give us some clues about how massive volcanoes can form,” Sager says. “An immense amount of magma came from the center, and this magma had to have come from the Earth’s mantle. So this is important information for geologists trying to understand how the Earth’s interior works.”

Image: Will Sager

While the planet warmed steadily at a rate of 0.13° C per decade since 1950, since 1998 it’s been on a hiatus, despite the fact that levels of carbon dioxide, the main greenhouse gas produced by human activities, continued a steady rise, reaching 400 parts per million for the first time in human history in May 2013.

Two researchers from Scripps Institution of Oceanography at UC San Diego discovered the reason for this hiatus, publishing their findings last week in Nature.

The reason for the warming break? Cooling in the eastern tropical Pacific Ocean. The team predicts that long-term global warming will resume when the tropical Pacific switches back to a warm state.

The researchers arrived at their conclusion using innovative computer modeling methods to simulate regional patterns of climate anomalies. This enabled them to see global warming in greater spatial detail, revealing where it has been most intense and where there has been no warming or even cooling.

The current cooling phase began just after a strong El Niño year in 1998. The study considers the tropical Pacific Decadal Oscillation (PDO), a climate cycle that plays out over the course of several decades. Within this large pattern fall El Niño and La Niña, well-known faster cycles that cause shifts in the distribution of warm water in the equatorial Pacific Ocean. While El Niño and La Niña last only a few years, the PDO lasts several decades. The last time it was in a cooling phase—cooling waters in the eastern equatorial Pacific Ocean—it lasted from roughly 1940 to the early 1970s. The researchers are unsure how this long this phase will last.

“That speaks to the challenge in predicting climate for the next few years,” says study co-author Shang-Ping Xie.  “We don’t know precisely when we’re going to come out of [the hiatus] but we know that over the timescale of several decades, climate will continue to warm as we pump more greenhouse gases into the atmosphere.”

“These compelling new results provide a powerful illustration of how the remote eastern tropical Pacific guides the behavior of the global ocean-atmosphere system, in this case exhibiting a discernible influence on the recent hiatus in global warming,” says Dan Barrie, program manager at the NOAA Climate Program Office.

Image: Kosaka, Xie/Scripps

Those of us who live in the western United States learn to expect forest fires as an unwelcome, annual occurrence. And, the Sierra Rim Fire is no exception. But the size, heat and proximity to Yosemite and Hetch-Hetchy have taken many of us by surprise.

We thought we’d highlight some of this week’s visuals and stories surrounding the blaze.

Videos
We’ve seen timelapses of fog, auroras, and the four seasons, so why not the Rim Fire as viewed from Yosemite National Park? It’s equally stunning.

This link was included in a blog post yesterday from Discover, with this astonishing fact about the fire that started on August 17:

It has now consumed 300 square miles — an area nearly two thirds as large as the sprawling City of Los Angeles — making the blaze the sixth largest in California history.

How about a bird’s-eye view of the blaze? Well, these videos posted by KQED News actually show us a pilot’s-eye view, courtesy of the National Guard.

From Space
Not high enough for you? NASA released images this week of the huge fire from two different satellites. One, from Suomi NPP, shows infrared images of the fire gaining ground over days. The other, from the Terra spacecraft, displays the trail of smoke the fire causes. The smoke can also be seen from the International Space Station, as seen in this image.

We found these images via the Bad Astronomer, who also posted this link on his site, where you can get up-to-date information about the fire, including a projected containment date of Friday, September 20th, 2013.

More images and numbers
National Geographic (of course) offers several beautiful and heartbreaking images from the ground. Their site also offers an article that provides some numbers from the fire: 4,000 firefighters fighting a fire that will be “20 percent contained by [this past] Wednesday” and “has involved 16 helicopters, 49 bulldozers, 454 fire engines, and 39 water tenders, wheeled tankers that transport water.” The same article explores the history of this type of large-scale firefighting.

Devastation
The large fire is burning through these wild lands, devastating wildlife along the way and wreaking havoc on the San Francisco’s water and electricity sources at Hetch-Hetchy. City and state officials have declared a state of emergency, reports the New Scientist.

Climate change
New Scientist also sees this as “a taste of things to come”:

Wildfires have always been a part of life in the US west, but they are on the rise as climate change takes hold. In California’s Sierra Nevada mountains, the main problem is the earlier onset of spring.

National Geographic echoes these sentiments, stating that fires this size might be the “new normal.” And a study by Harvard scientists, out this week, comes to the same conclusion. It suggests that because of our warming world, wildfire seasons will be about three weeks longer by 2050, up to twice as smoky, and will burn a wider area in the western states.

The aftermath
Finally, Brandon Keim at Wired offers a glimpse of what the landscape may look like post-fire, reminding us that fire is a “natural, inevitable phenomenon, and one to which western North American ecologies are well-adapted, and even require to sustain themselves.”

Image: US Department of Agriculture

What’s going on with the oceans and what can we do?

As carbon dioxide (CO₂) rises in our atmosphere, the oceans absorb roughly a quarter of the amount. This lowers the pH level in the seawater, making the oceans more acidic. How this affects life in and out of the sea is continually studied.

This week, ocean acidification is the topic of several scientific papers. We thought we’d highlight a few of them here.

Nature Climate Change has two papers—one about the affect of acidification on several different species, and the other on how ocean acidification causes even more global warming.

For the first paper, German researchers surveyed previous studies that dealt with the consequences of ocean acidification for marine species from five animal taxa: corals, crustaceans, mollusks, fish, and echinoderms. By the end, they had compiled a total of 167 studies with the data from more than 150 different species.

Their findings? Different species are affected in different ways and to different extents, but all species are negatively affected by ocean acidification. “Our study showed that all animal groups we considered are affected negatively by higher carbon dioxide concentrations. Corals, echinoderms, and mollusks above all react very sensitively to a decline in the pH value,” says lead author Astrid Wittmann, of the Alfred Wegener Institute.

The second study demonstrates that the negative effects of ocean acidification aren’t just limited to marine life. The authors discovered that rising ocean acidity has the potential to amplify climate warming in general, through the decreased production of a biogenic sulfur compound.

Phytoplankton in the ocean produce dimethyl sulfid (DMS). As DMS is released into the air, it creates atmospheric sulfur—which increases the reflectivity of the atmosphere to incoming radiation, reducing surface temperatures. Warming acidic oceans means the phytoplankton produce less DMS, causing an even warmer planet.

In addition to the Nature papers, Philosophical Transactions of the Royal Society B has an ocean acidification-themed issue this week, with nine papers studying its effects. The papers describe three distinct effects on marine life due to ocean acidification: species interactions, decreased ecosystem functions, and adaptations. Andrew Revkin has a great summary of them on his Dot Earth blog in the New York Times.

“It’s great that some of these papers are looking at entire ecosystems,” says Aaron Pope, the Academy’s sustainability manager who works tirelessly to communicate ocean acidification issues. “There’s been lots of research in the past on individual species impacts, but data on entire natural systems was missing. Now we can start to talk about what will really happen in marine ecosystems as ocean acidification gets worse.”

One paper of the group (from local researchers at San Francisco State University) looks at tiny coccolithophores. These single-celled algae are able to sequester oceanic carbon by incorporating it into their shells, providing ballast to speed the sinking of carbon to the deep sea. The little organisms are central to the global carbon cycle, a role that could be disrupted if rising levels of atmospheric carbon dioxide and warming temperatures interfere with their ability to grow their calcified shells.

This paper might provide a bit of hope among the rest: “At least in this experiment with one coccolithophore strain, when we combined higher levels of CO₂ with higher temperatures, they actually did better in terms of calcification,” says co-author Jonathon Stillman, of SF State.

Here’s to hoping that all of these papers findings will create more awareness of ocean acidification that will lead to more solutions.

Coccolithophore image: Alison R. Taylor/PLoS Biology

As scientists understand more about microbes, it seems that the miniscule life forms have the potential to contribute to a host of useful activities—making biofuels, fighting human disease, improving high tech, you name it!

Now, a feature article in the September issue of Scientific American looks at how soil microbes could revolutionize agriculture.

Soil microbes include everything from bacteria to fungi, and article author Richard Conniff likes to call the lot collectively “the agribiome.” These microscopic life forms have the potential to solve many crises facing agriculture today—everything from climate change and drought to Salmonella and other food-bourn illnesses, from the costs of man-made fertilizers to the GMO controversy.

Conniff’s article comes on the heels two other papers that highlight the importance of soil microbes. In a paper published last week in the Proceedings of the National Academy of Sciences, a team of British scientists emphasizes how important soil microbe diversity is for European crops. And two weeks ago, American researchers determined that soil microbes are responsible for controlling carbon in the soil—an important factor in retaining the important mineral in the dirt as temperatures rise and the climate warms.

The Scientific American article gives many examples of these crucial, unseen microbial workers. Bacteria found in soil on the United States West Coast can kill Salmonella, Conniff reports, so the USDA is looking at introducing the bacteria in East Coast soils to stop the occasionally deadly outbreaks.

And instead of genetically modifying actual crops to withstand drought conditions, Mexican scientists are looking at modifying bacteria to strengthen the plants in the soil at their roots.

Mycorrhizal fungi in the soil are heroes in both the SciAm article and the PNAS study. The fungi deliver much-needed phosphate to crops, an easier and cheaper way to get the important mineral to the plants to help them grow. Artificial fertilizers can be expensive, especially for farmers in developing countries, and harm the natural soil ecosystem. Run-off from these fertilizers also contaminates freshwater and marine environments. A simple animation of how the fungi works to help plants is available here.

(Mycorrhizal fungi also play a heroic role in the next Academy planetarium show! Currently in production and set for a fall 2014 opening date, the latest production from our visualization studio will highlight the complex relationships in ecosystems—and how humans fit into the picture.)

If farmers and scientists can acknowledge that collaborating with microbes can play a crucial role in farming, “we will have come a step closer to feeding a hungry world,” Conniff concludes.

The lead author of the PNAS paper, Franciska de Vries, says, “This research highlights the importance of soil organisms and demonstrates that there is a whole world beneath our feet, inhabited by small creatures that we can’t even see most of the time. By liberating nitrogen for plant growth and locking up carbon in the soil they play an important role in supporting life on Earth.”

Mycorrhizal fungi image: Nilsson et al. BMC Bioinformatics

Top predators (think sharks, lions, wolves) may eat many animals within an environment, but they also keep the ecosystem in check.

This may seem counter-intuitive, but according to science writer Mary Ellen Hannibal, “We need a full complement of species on wild landscapes so that nature can fulfill its whole cycle.  It turns out that top predators—the wolf, for example—play an outsize role in keeping the whole system together.”

This was, in fact, the subject of her very excellent OpEd piece in the New York Times last fall entitled, “Why the Beaver Should Thank the Wolf.”

And scientific studies reflect this, too. A study out this week in the Journal of Animal Ecology demonstrates why the grizzly bear should also thank the wolf.

Bill Ripple, Bob Beschta, and their colleagues discovered that the return of wolves to Yellowstone National Park is beginning to bring back a key part of the diet of grizzly bears that has been missing for much of the past century—berries that help bears put on fat before going into hibernation.

“Wild fruit is typically an important part of grizzly bear diet, especially in late summer when they are trying to gain weight as rapidly as possible before winter hibernation,” Ripple says. “Berries are one part of a diverse food source that aids bear survival and reproduction, and at certain times of the year can be more than half their diet in many places in North America.”

Looking at bear scat, the researchers found that the level of berries consumed by Yellowstone grizzlies is significantly higher now that shrubs are starting to recover following the re-introduction of wolves, which have reduced over-browsing by elk herds. The berry bushes also produce flowers of value to pollinators such as butterflies, insects, and hummingbirds; food for other small and large mammals; and special benefits to birds.

When wolves were removed from Yellowstone early in the 1920s, increased browsing by elk herds caused the demise of young aspen and willow trees—a favorite food—along with many berry-producing shrubs and tall, herbaceous plants. The recovery of those trees and other food sources since the re-introduction of wolves in the 1990s has had a profound impact on the Yellowstone ecosystem, researchers say.

Hannibal points out that Beschta and Ripple didn’t set out to study wolves. In an email to Science Today, she says, “They set out to study the health of the Lamar River… But in looking for a cause to explain the degradation of the river, what they found is that super-abundant elk were eating the vegetation down to the roots on the river banks, and the vegetation wasn’t able to ‘recruit,’ or grow up strong and healthy. When wolves were reintroduced to Yellowstone, the vegetation started to recover. Beschta and Ripple and many other scientists documented this and analyzed it, and it turns out that elk change their behavior when wolves are around, and they stay on the move, which gives the vegetation time to recover.”

“Studies like this point to the need for an ecologically effective number of wolves,” Beschta says in a press release. “As we learn more about the cascading effects they have on ecosystems, the issue may be more than having just enough individual wolves so they can survive as a species. In some situations, we may wish to consider the numbers necessary to help control overbrowsing, allow tree and shrub recovery, and restore ecosystem health.”

Beschta’s and Ripple’s work is featured in Hannibal’s Spine of the Continent, a great story of conservation efforts to create wildlife corridors to protect these top predators and the ecosystems that depend on them. Look for more of these stories here in Science Today, and in an Academy exhibit, Life Connected, opening in Spring 2014.

Image: Bobisbob at en.wikipedia