By Henry Fountain
Published: December 6, 2005
Take Me to Your Methanogen
The Greenland Ice Sheet Project 2, a five-year drilling effort that ended in 1993, produced a core 10,015 feet long, representing about 110,000 years of ice accumulation.
The core has been used to study long-term climate fluctuations. Measurements of atmospheric methane trapped in the ice, for example, have been used to show how global temperatures rose and fell over thousands of years.
But methane measurements at several points along the core, all within about 300 feet of the bottom, are much higher than all the others. The question for P. Buford Price and colleagues at the University of California, Berkeley, is what caused those methane spikes.
Their answer, derived after analyzing core samples in their lab, is that the gas did not come from the atmosphere, but was produced within the ice by primitive single-cell organisms called archaea.
The researchers suggest that the findings, reported in The Proceedings of the National Academy of Sciences, have implications for the possibility of life on Mars.
Microbes are found throughout ice cores like this, but the researchers found that concentrations were much higher at the excess-methane sites, and tests showed that a significant portion were methane-producers, or methanogens.
They suggest that since this ice is so close to the base ice of the core, which is heavily laden with silt, the methanogens probably got into the ice through the normal turbulence and overturning that occurs in flowing glaciers.
Recent studies have shown that the Martian atmosphere contains a very small amount of methane. Because the gas is broken down by ultraviolet radiation from the Sun, replacement must be happening somehow. The source could be a nonbiological process, but some scientists have speculated that methane-producing microbes below the surface may be responsible.
Dr. Price and his colleagues estimated that very low concentrations of methanogens, on the order of one cell per milliliter, could produce the Martian methane.
Clay on Mars: That Means Water
Whether there are microbes deep within Mars is pure speculation at this point. Very little is known about the interior of the planet.
Even much about the surface of Mars is a mystery. For one thing, there is plenty of photographic evidence -- deltas, valleys and other features -- that the planet once had a lot of water.
And water working on igneous rock (which Mars has in abundance) should produce clays, which, very simply put, consist of layers of minerals with water trapped between them.
But there has not been definitive evidence of clays on the planet.
Now there is. Using data from a spectrometer aboard the Mars Express spacecraft, Fran?s Poulet of the University of Paris-South and colleagues have found ample evidence for phyllosilicates on Mars. Clays are a subcategory of phyllosilicates.
The clays were found in outcroppings in the Martian highlands, which were formed more than three billion years ago, relatively early in the planet's history. So they support the idea that Mars had an active hydrological system back then; long-term contact with water is needed for the formation of clays.
The finding is reported in the journal Nature.
Crab (the Nebula) in All Its Glory
Backyard astronomers know the Crab Nebula well; it is often one of the first targets for someone just getting interested in the hobby. But even though it is six light-years across, in a small telescope the nebula is a wisp of an object.
It takes a large telescope, and particularly the Hubble, to show the crab in all its glory.
A new image of the nebula, consisting of a mosaic of 24 Hubble images taken in 1999 and 2000, is online at hubblesite.org.
The weblike remains of the exploding star (the nebula is a supernova that occurred in 1054) can be seen, and the neutron star that resulted gives the interior of the image a bluish glow.
When a Giant Walked the Earth
Martin A. Whyte is a dinosaur hunter by profession, stalking the remains of the beasts in Yorkshire, England. But no matter where he is, Dr. Whyte is always on the lookout for signs of ancient life.
So it's no surprise that Dr. Whyte, a professor at the University of Sheffield who is also a geologist, discovered a fossil track one summer day in 2003, when he took time from studying the geology of the central Scottish coast to stroll on the beach.
Dr. Whyte's analysis of what made those tracks, however, turned out to be a big surprise -- a giant water scorpion from 330 million years ago, long before the age of the dinosaurs. It is the first evidence that these long-extinct arthropods walked on land.
Dr. Whyte said the discovery was serendipitous. ''I found myself looking across a stretch of beach,'' he recalled, ''and I saw a rock face with this trackway going across.'' It consisted of a sinuous series of markings about 20 feet long, made in sand that had turned to rock.
''I knew as soon as I saw it, it was made by some kind of animal,'' he said.
It was clear from the markings that the creature had three limbs on each side. ''Right away that eliminated the reptiles and amphibians,'' Dr. Whyte said. ''I had to consider some sort of arthropod.''
The track also had a large central groove, obviously made by a heavy tail. And the animal must have been huge, about 5 feet long and 3 feet wide. Dr. Whyte decided it could only be a species of Hibbertopterus, water scorpions that are distant ancestors of modern creatures like horseshoe crabs.
Just fragments of Hibbertopterus fossils exist. Some are from specimens the size of the one that left the tracks, Dr. Whyte said.
The stride is very short, indicating it moved very slowly and probably in a herky-jerky manner. That its tail dragged-- the groove it left partly obscured some of the footprints -- is strong evidence that the creature was walking across land. ''This animal was in no way buoyed up by water,'' he said.
At this point in the earth's history, the earliest four-legged animals were coming out of the water onto land. But water scorpions did not make such a transition. Dr. Whyte said this specimen was probably out of the water a short time, as its gill-like breathing apparatus needed to remain wet. So it might have been walking from one body of water to another one nearby.
''The best I can say is it's going from somewhere to somewhere,'' he said. ''It's nice to speculate that it might have come out for spawning or to look for a beach party or whatever. But there's just no evidence for that.''
Drawing (Drawing by Chris Gash)