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

Oh, is that all?

Cameron is not a scientist, but a proponent of science, as he described at a press conference yesterday. (And scientists need more people like him on their side!) In this role, he hopes to bring science into the popular dialogue and provide tools to scientists—whether that’s funding (through different sources including his Blue Planet Marine Research foundation) or engineering (such as his Deepsea Challenger submersible).

This past March, Cameron and a team of scientists headed to the Mariana Trench in the Pacific Ocean. Using his submersible as well as two unmanned landers, Cameron gradually dove deeper and deeper into the Mariana Trench, collecting samples and video for scientists.

At the AGU meeting, researchers described their findings at these depths and locations. Kevin Hand, an astrobiologist with NASA’s Jet Propulsion Laboratory, spoke of microbial mats and the serpentinization that he witnessed. Doug Bartlett, a microbiologist from Scripps Institution of Oceanography at UC San Diego, discussed not only the many novel microbes discovered, but also the larger organisms found at some of these depths, including crustaceans, worms, corals and anemones. Patricia Fryer, a geologist from the University of Hawaii, described the tectonic plates, subduction zone and topography at that location.

Together, the findings describe a rich and unique ecosystem. With no other resources to feed the microbes, the researchers propose that the serpentinization on the overriding subduction plate is the energy source for microbes and microbial mats at those depths. Those microbes in turn feed the larger animals seen in the area.

Cameron and the scientists go a step further, suggesting that the serpentinization’s match of geochemistry and biochemistry could be how life began on this planet. And what’s more, this could be how life works in other water bodies in our Solar System and beyond. Cameron named the moons Enceladus, Europa and Callisto as potentially harboring these processes.

We have much to learn about this unusual spot on our planet, 35,630 feet below sea level, and Cameron’s quest is a boon for marine science. Even though the proposed theories about the origin of life seem a bit premature, just focusing on the “unexplored frontiers right here on Earth,” in Cameron’s words, is enough. Isn’t it?

Image: Kmusser/Wikipedia using NOAA data

]]> http://www.calacademy.org/sciencetoday/diving-deep-for-science/559483/feed/ 0 http://www.calacademy.org/sciencetoday/life-near-the-asteroid-belt/559244/ http://www.calacademy.org/sciencetoday/life-near-the-asteroid-belt/559244/#comments Fri, 09 Nov 2012 20:53:32 +0000 molly http://www.calacademy.org/sciencetoday/?p=9244 What planetary conditions does life require to evolve? Astronomers ask this question often as they search the Universe for a place like Earth. Water seems to be a necessity. So does maintaining the right distance from a parent star (think habitable zone). What about an asteroid belt?

Two researchers hypothesize that an asteroid belt, just the right size and distance from its star, might be necessary for a star system to support a life-bearing planet.

This might sound surprising, since asteroids can occasionally impact Earth and trigger mass extinctions. Ouch! But an emerging view proposes that asteroid collisions with planets may provide a boost to the birth and evolution of complex life.

For one thing, asteroids delivered water and organic compounds to the early Earth. Consistent with the theory of punctuated equilibrium, occasional asteroid impacts might also accelerate the rate of biological evolution by disrupting a planet’s environment to the point that species must evolve new adaptation strategies.

Rebecca Martin, of the University of Colorado, and Mario Livio, of the Space Telescope Science Institute, looked at our solar system and used theoretical models and actual observations of other star systems and exoplanets to study the theory that life needs an asteroid belt.

They suggest that the location of an asteroid belt relative to a Jupiter-like planet is particularly favorable to life. The asteroid belt in our solar system, located between Mars and Jupiter, is a region of millions of space rocks sitting near the “snow line,” beyond which volatile materials such as water ice are far enough from the Sun’s heat to remain intact.

Our solar system’s formation was just right for life, Livio says. “To have such ideal conditions you need a giant planet like Jupiter that is just outside the asteroid belt [and] that migrated a little bit, but not through the belt,” he explains. “If a large planet like Jupiter migrates through the belt, it would scatter the material. If, on the other hand, a large planet did not migrate at all, that, too, is not good because the asteroid belt would be too massive. There would be so much bombardment from asteroids that life may never evolve.”

Using our solar system as a model, Martin and Livio proposed that asteroid belts in other solar systems would always be located approximately at the snow line. They created models of protoplanetary disks, the dense gas and dust around a newly formed star; then they looked at observations from NASA’s Spitzer Space Telescope of 90 such regions that have warm dust, which could indicate the presence of an asteroid belt-like structure. The warm dust fell right near the snow line.

But for life to exist, the system also needs a large gas giant, like Jupiter, to “manage” the size of the asteroid belt. So Martin and Livio looked at data for 520 giant planets found outside our solar system. Only 19 of them reside outside the snow line, suggesting that most of the giant planets that formed outside the snow line have migrated too far inward to preserve the right-sized asteroid belt needed to foster life on an Earth-like planet near the belt. The team calculated that less than four percent of the observed systems may actually harbor such a compact asteroid belt.

“Our study shows that only a tiny fraction of planetary systems observed to date seem to have giant planets in the right location to produce an asteroid belt of the appropriate size, offering the potential for life on a nearby rocky planet,” says Martin. “Our study suggests that our solar system may be rather special.”

Their findings are published in the Monthly Notices of the Royal Astronomical Society: Letters.

Image: NASA, ESA, and A. Feild (STScI)

Dave Ebert, research associate at the Academy and director of the Pacific Shark Research Center, recently had that honor. His colleagues have bestowed the name Trilocularia eberti to a new species of cestode (tapeworm), described in a recent article.

T. eberti is a shark parasite, and Ebert is currently working on a description of said shark, discovered in South Africa. That is Ebert’s true occupation, discovering and naming new shark species. Not that life as a tapeworm name muse wouldn’t be fulfilling…

“Since I study sharks I always thought I would have either a cool shark, skate or chimaera named after me, so the fact it was a cestode was quite a surprise,” Dave says. “Of course having a gut parasite named after oneself lends itself to jokes by friends and colleagues. However, it is the first time I have ever had any organism named after me, so I am quite honored.”

And T. eberti is pretty special. It’s only the second member of its genus to be named.  This specialized group of cestodes appears to parasitize members of the shark genus Squalus, commonly known as spiny or spur dogfish, and this newest species resides in the intestinal valve of the shark. Good living!

Ebert isn’t the first Academy researcher to have a species named for him. You might remember our own Bob Drewes’ delight when he had a small phallic mushroom named after him—Phallus drewesii.

What new species do you imagine being named after you?

Image: Dave Ebert

Even if there are a number of planets that could support tectonics, running water and the chemical cycles that are essential for life as we know it, it seems unlikely that any of them would look like Earth.

The reason? Plants.

A series of articles in the journal report that both vascular and non-vascular plants (mosses, liverworts, algae) shaped the surface of Earth, affecting the oceans and climate of our planet as they began to appear 470 million years ago.

Vascular plants defined the way water flowed on the Earth. One article describes the interplay of plant evolution and river formation. Scientific American offers a summation:

Before the era of plants, water ran over Earth’s landmasses in broad sheets, with no defined courses. Only when enough vegetation grew to break down rock into minerals and mud, and then hold that mud in place, did river banks form and begin to channel the water. The channeling led to periodic flooding that deposited sediment over broad areas, building up rich soil. The soil allowed trees to take root. Their woody debris fell into the rivers, creating logjams that rapidly created new channels and caused even more flooding, setting up a feedback loop that eventually supported forests and fertile plains.

Another article in Nature Geoscience examines how early non-vascular plants affected the planet dramatically—causing global cooling and mass extinction in the oceans. British researchers working in the lab and with computer simulations discovered that these first plants caused the weathering of calcium and magnesium ions from silicate rocks, such as granite, in a process that removed carbon dioxide from the atmosphere, forming new carbonate rocks in the ocean. This cooled global temperatures by around five degrees Celsius.

In addition, by weathering the nutrients from rocks, the first plants increased the quantities of both these nutrients going into the oceans, fuelling productivity there and causing organic carbon burial. This removed yet more carbon from the atmosphere, further cooling the climate by another two to three degrees Celsius. It could also have had a devastating impact on marine life, leading to a mass extinction that has puzzled scientists.

The effect of plants on our planet is profound, remarks Liam Dolan of Oxford University, a researcher on the non-vascular plant study.

For me the most important take-home message is that the invasion of the land by plants—a pivotal time in the history of the planet—brought about huge climate changes. Our discovery emphasizes that plants have a central regulatory role in the control of climate: they did yesterday, they do today and they certainly will in the future.

Image: Dog Walking Girl/Wikipedia

Britney Schmidt, a postdoctoral fellow at the University of Texas at Austin, and her team were perusing data from the Galileo spacecraft. From 1995-2003, the Galileo mission studied Jupiter and some of its 64 moons, sending back a wealth of data that scientists are still studying today.

Several images of the icy moon Europa caught the team’s attention—especially those of roughly circular, bumpy features on its surface called chaos terrains. These chaos terrains looked familiar to the researchers, much like ice fields in Greenland and Antarctica here on Earth.

On our planet, these features correspond to ice shelves that sit on oceans or glaciers that cover volcanoes. The scientists wondered if the chaos terrains could be formed in similar ways and developed a model to test their theory.

Data from Galileo already suggested the existence of a saltwater ocean well below the surface of Europa—an ocean that contains more liquid water than all of Earth’s oceans combined! However, being so far from the Sun, the ocean surface is completely frozen. Most scientists think this ice crust is tens of miles thick.
“One opinion in the scientific community has been if the ice shell is thick, that’s bad for biology. That might mean the surface isn’t communicating with the underlying ocean,” said Schmidt at a NASA press conference yesterday.

But the bumpy surface could be good for biology. Schmidt’s model shows the chaos features on Europa’s surface may be formed by mechanisms that involve significant exchange between the icy shell and underlying lakes, equal in volume to North America’s Great Lakes.

These mechanisms could transfer nutrients and energy between the surface of the planet and the vast global ocean already inferred to exist below the thick ice shell. Which could increase the potential for life there.

“Now, we see evidence that it’s a thick ice shell that can mix vigorously and new evidence for giant shallow lakes. That could make Europa and its ocean more habitable,” reported Schmidt.

Still, because the lakes (if they exist) would lie a few miles below the surface, the only true confirmation of their presence would come from a future spacecraft mission designed to probe the ice shell.

So we’ll have to wait to confirm life on Europa, according to Wired.

Unfortunately, NASA does not currently have missions to explore Europa on its schedule… A proposed Jupiter-Europa Orbiter has an estimated price tag of $4.6 billion, making it unlikely to launch during a time of budget squeezes.

The research appears in the current edition of Nature.

Image: Britney Schmidt and Dead Pixel FX, University of Texas at Austin

Villy Christensen of the University of British Columbia (UBC) said, “Yes, there will be fish left, but it will be a very different ocean from the ones your parents and grandparents knew and even different from now.”

The biggest difference? Large, predatory fish will be gone.

In fact, over the last one hundred years, the population of these large, top-of-the-food-web fish has declined by two-thirds, half of that decline occurring only in the last 40 years. And that population continues to decline.

There will be many small fish left, but not necessarily the ones we eat.

He and his colleague, Reg Watson, also from UBC, are working with scientists, governments and NGOs to build a global database of fishing efforts to truly understand what’s going on in the world’s oceans.

Seventy-six million tons of fish are consumed each year, and Watson found that we are fishing harder for the same or less result. It’s possible that we’ve hit “peak fish,” according to Watson. Jacqueline Alder of the UN Environment Program in Kenya is working with the UBC group, looking at their models in terms of marine biodiversity and sustainability. She urged that we must reduce fishing efforts immediately to allow fish stocks to rebuild.

In addition, there was much discussion around the non-sustainability of using fish for feedstock in aquaculture and agriculture– fish we are not directly eating. The science and technology have to get better to use plant-based feedstock for fish farms.

Christensen stressed this is a large view of what’s going on in the entire ocean ecosystem, not just one area or species.

For more focused, local information, read our recent article on banning shark finning, and the San Francisco Chronicle had a devastating article last week stating that some of the fish in the Delta may be too far gone to save from extinction.

Image: Mila Zinkova/Wikimedia