Friday, January 24, 2014

Fossil fish re-defines origins of walking


Color illustration of Tiktaalik swimming and walking in water. (Source: Kalliopi Monoyios/University of Chicago)

Jennifer Viegas
Discovery News

Fossils of a creature that looked part-fish and part-limbed animal, the precursor to walking land animals, were recently found in northern Canada, according to a new study.

The beastie, Tiktaalik roseae, represents the best-known transitional species between fish and land-dwelling animals, according to researchers.

The fossil, described in this week's edition of Proceedings of the National Academy of Sciences, lived 375 million years ago.

"Tiktaalik was a combination of primitive and advanced features," says co-author Edward Daeschler, Associate Curator of Vertebrate Zoology at the Academy of Natural Sciences of Drexel University.

While classified as a fish, Tiktaalik looked like a cross between a fish and a crocodile. It could grow to nearly 3 metres in length, and likely spent its days hunting in shallow freshwater environments. It had gills, scales and fins, but also had features associated with terrestrial animals. These included a mobile neck, a robust ribcage and primitive lungs.

Of most interest to the researchers, its large forefins had shoulders, elbows and partial wrists, which allowed it to support itself on ground.

The presence of these limb-like features challenges the theory that such mobile hind appendages developed only after species transitioned to life on land.

"Previous theories, based on the best available data, propose that a shift occurred from 'front-wheel drive' locomotion in fish to more of a 'four-wheel drive' in tetrapods (four-footed animals)," says co-author Neil Shubin, who is a professor of Anatomy at the University of Chicago. "But it looks like this shift actually began to happen in fish, not in limbed animals."

Some modern fish can walk, such as the African lungfish. Lungfish often look like they are slithering, more than walking, but if you see them in an aquarium, their little limbs are evident, and they do walk around.

It's likely that Tiktaalik did the same, with its later relatives walking completely out of water and onto land, where they eventually evolved into land animals.

"Regardless of the gait Tiktaalik used, it's clear that the emphasis on hind appendages and pelvic-propelled locomotion is a trend that began in fish, and was later exaggerated during the origin of tetrapods," Shubin says.

Old trees 'star players' in carbon uptake

The researchers found that old-growth forests shouldn't be left out of the carbon trading equation (Source: Markku Saarinen)

Anna Salleh
ABC

The largest trees in the world grow more quickly, and thus take up more carbon dioxide, than younger, smaller trees, say researchers.

The findings, published today in the journal Nature add to our understanding of how tree growth rates change over time.

"We found that tree growth rates increased continuously with tree size so, on average, the biggest trees in the forest are the fastest growing trees in the forest in terms of mass", says lead author, Dr Nate Stephenson, a research ecologist with the US Geological Survey.

Stephenson says the majority view to date has been that trees have a similar growth pattern to humans - starting off slowly, getting a growth spurt in adolescence, and then slowing down again as they get older.

But, he says, a number of scientists have argued trees continue to grow faster and faster the larger they get.

"It turns out that that's the case for the large majority of tree species."

Stephenson says the latest evidence comes from the largest study to date on the growth rate of trees across the globe.

He and colleagues measured the change in diameter of 650,000 individual trees from 403 species in both temperate and tropical areas.

"On average, every year trees put on more mass than they put on the year before," says Stephenson.
"Old trees are the ones putting on the most bulk in old forests. They are the star players."

"We think it strongly supports the minority view about tree growth rate."

Paradox

Stephenson says the majority view has been supported by previous research that, among other things, has shown as a tree gets older its growth rate per leaf decreases.

"A given leaf on a big tall eucalyptus tree photosynthesises less than one on a smaller tree," says Stephenson.

Studies have also found that, overall, older forest stands grow at a slower rate compared to younger stands.

But, says Stephenson, such measurements have been made at the scale of individual leaves and at the scale of forest stands.

"Most people have just inferred that the same has to be happening at the scale of the individual tree but it's not," he says, adding the latest findings are not incompatible with earlier observations at the leaf and forest stand scales.

"Our observation is compatible with those other observations but it just may not be intuitive," says Stephenson.

He says even though productivity per leaf in older trees decreases, this is counteracted by the fact that these trees have a lot more leaves that collectively result in the tree's faster growth rate.

"A tree that is a metre in diameter has, on average, 100 times as much leave mass as one that is only 10 centimetres in diameter."

At the other end of the scale, more young trees than old trees are packed into the same area of forest, and so this explains why collectively forest stands consisting of young trees put on more mass than those consisting of fewer old trees.

Implications

Stephenson says the findings will have implications for our understanding the role of trees in the carbon cycle and greenhouse gas concentrations in the atmosphere.

"We already know that the biggest trees are the most important ones to preserve for carbon sequestration because they already hold so much carbon in them. It think the finding adds a little more support to the idea we need to protect these big trees," he says.

"Not only do they hold the most carbon but they are putting on a huge amount every single year."

Mars once had fresh water on surface

Data from the Opportunity rover on the rim of Endeavour crater indicates an asteroid impact changed Martian water forever (Source: NASA)

Stuart Gary
ABC

The surface of Mars once flowed with water fresh enough to sustain life, according to data collected by two of NASA's Martian rovers.

The findings, published in the journal Science, suggest freshwater rivers and streams once existed in the Meridiani Plains region near the Martian equator, 3.8 billion years ago.

But all that changed when a huge asteroid impact turned the fresh water into a highly acidic soup.
"All the evidence we have indicates the local Martian water was like spring water that you could drink," according CSIRO's Dr Paulo de Souza, a scientist with NASA's Mars exploration rover program.

"It would have been hospitable to any microbial life that may have existed at the time."

But, according to de Souza, the asteroid impact exposed volcanic rocks that were then subjected to chemical weathering, resulting in salts dissolving into the water.

"As time passed with this and other impacts in the region, a more acidic environment developed, with the water becoming as strong as vinegar," he says.

De Souza and colleagues can determine the chemistry of the water based on the different types of minerals formed in the sediments left behind.

"We not only know that there was water on Mars, but we can see how that water changed over time forming different minerals," says de Souza.

"Looking at those minerals is just like looking at a book of history, with the story of the planet recorded in those minerals."

Eyes in the sky

The researchers sent Opportunity to investigate part of the Endeavour Crater rim where NASA's Mars Reconnaissance Orbitor spacecraft detected iron- and aluminium-rich clay minerals.

The rover sampled a geological feature called the Matijevic formation, a grouping of fine-grained, layered rocks enriched with clay minerals.

Analysis of the spherules, veins and fractures in these mineral rich rocks indicates the Matijevic formation predates the impact event that formed Endeavour crater.

They represent the oldest Martian rocks, as well as the earliest evidence of water activity, so far encountered by Opportunity.

The authors found these older rocks were formed in conditions that would have been favourable to life or prebiotic chemistry.

"The formation on the rim of this crater had evidence of a more suitable environment for life to form and evolve in fresh water," says de Souza.

"We haven't actually found the fresh water, that would have been there four billion years ago, but what we saw were the minerals that could only be formed if we have fresh water present."

Meanwhile, the younger rocks sitting on top of the formation, which are believed to date from after the impact event, contain signatures for super-salty, highly-acidic water, which would have made life tough for even the hardiest extremophile microorganisms.

Ongoing mission

NASA's twin six-wheeled Mars exploration rovers, Spirit and Opportunity, landed on opposite sides of the red planet in January 2004, on what was expected to be a 90-day mission to search for geological evidence of past water.

Spirit's mission ended in March 2010, however its twin Opportunity is still exploring the red planet, ten years after landing.

"We've travelled over 38 kilometres across the surface of Mars ... Opportunity has just come out of another Martian winter," says de Souza.

"And a wind storm the other day has cleared the dust off the rover's solar panels."

According to de Souza, that means despite a decade of service, there's lots more science that can still be done.

Monday, January 6, 2014

'Dark Matter Disc' Discovered Over The Equator?

A disc of dark matter might have just been found hanging over the Equator of the Earth. But don't panic.

The startling claim has been made by a scientist examining why the Earth appears to be slightly heavier than previously thought.

Dark matter is the almost-theoretical substance which helps explain why there is nowhere near enough visible matter in the universe to account for the way it's developed since the Big Bang.

But while most models of the universe suggest dark matter is abundant, experiments have tried (and so far mostly failed) to find direct evidence of it.

Now one scientist says it might have been hanging above our heads the entire time.

Ben Harris, from the University of Texas, said at the American Geophysical Union that GPS data implies the Earth is heavier than it 'should' be.

The difference between the number he's calculated, and that taken as read by the International Astronomical Union, could be caused by the presence of nearby Dark Matter, he thinks.

In his study, Harris used data from the European Galileo, U.S., GPS, GLONASS and Russian satellite groups, and measured the weight of the Earth. His result is 0.005-0.008 percent bigger than current estimates. A disc of dark matter over the equator could account for the difference, he said - being picked up by satellites overhead while being missed by regular methods used to weigh our planet.
This disc would be 191 kilometres thick and 70,000 km wide, he suggests.

However, we have to add a hefty load of caveats here. First, there are potential flaws with the methodology. New Scientist points out that the study doesn't account for subtle changes in the orbit of satellites caused by relativity and the gravity of the sun and moon. It's also pretty much conjecture, even if the data is accurate - there is no direct evidence of dark matter above our Earth, and much more study would be needed to get it.

On the other hand, if 80% of our universe really is dark matter, it wouldn't be crazy to think there would be some nearby. If only it wasn't so - well - dark, we might just be able to see it in plain sight very close to home indeed.