Archive for the ‘Life’ Category

Life on land four times older than previously thought

July 23, 2013

“Settled science” has had it that life on land dates from about 500 million years ago. But fossils of something rather simpler than plants or animals found in South Africa provide evidence that life on land could be 2.2 billion years old.

Gregory J. Retallack, Evelyn S. Krull, Glenn D. Thackray, Dula Parkinson. Problematic urn-shaped fossils from a Paleoproterozoic (2.2Ga) paleosol in South Africa. Precambrian Research, 2013; 235: 71

DOI:10.1016/j.precamres.2013.05.015

Science Daily: 

Conventional scientific wisdom has it that plants and other creatures have only lived on land for about 500 million years, and that landscapes of the early Earth were as barren as Mars.

A new study, led by geologist Gregory J. Retallack of the University of Oregon, now has presented evidence for life on land that is four times as old — at 2.2 billion years ago and almost half way back to the inception of the planet.

That evidence, which is detailed in the September issue of the journal Precambrian Research, involves fossils the size of match heads and connected into bunches by threads in the surface of an ancient soil from South Africa. They have been named Diskagma buttonii, meaning “disc-shaped fragments of Andy Button,” but it is unsure what the fossils were, the authors say.

“They certainly were not plants or animals, but something rather more simple,” said Retallack, professor of geological sciences and co-director of paleontological collections at the UO’s Museum of Natural and Cultural History. The fossils, he added, most resemble modern soil organisms called Geosiphon, a fungus with a central cavity filled with symbiotic cyanobacteria.

“There is independent evidence for cyanobacteria, but not fungi, of the same geological age, and these new fossils set a new and earlier benchmark for the greening of the land,” he said. “This gains added significance because fossil soils hosting the fossils have long been taken as evidence for a marked rise in the amount of oxygen in the atmosphere at about 2.4 billion to 2.2 billion years ago, widely called the Great Oxidation Event.”

By modern standards, in which Earth’s air is now 21 percent oxygen, this early rise was modest, to about 5 percent oxygen, but it represented a rise from vanishingly low oxygen levels earlier in geological time. …

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Tenacious life: Microbe swaps phosphorous for arsenic

December 2, 2010
Lakeside of the Mono Lake with Tufa columns in...

Mono Lake: Image via Wikipedia

The New York Times has the story that has been buzzing all day:

Scientists said Thursday that they had trained a bacterium to eat and grow on a diet of arsenic, in place of phosphorus — one of six elements considered essential for life — opening up the possibility that organisms could exist elsewhere in the universe or even here on Earth using biochemical powers we have not yet dared to dream about.

The bacterium, scraped from the bottom of Mono Lake in California and grown for months in a lab mixture containing arsenic, gradually swapped out atoms of phosphorus in its little body for atoms of arsenic.

Scientists said the results, if confirmed, would expand the notion of what life could be and where it could be. “There is basic mystery, when you look at life,” said Dimitar Sasselov, an astronomer at the Harvard-Smithsonian Center for Astrophysics and director of an institute on the origins of life there, who was not involved in the work. “Nature only uses a restrictive set of molecules and chemical reactions out of many thousands available. This is our first glimmer that maybe there are other options.”

Felisa Wolfe-Simon, a NASA astrobiology fellow at the United States Geological Survey in Menlo Park, Calif., who led the experiment, said, “This is a microbe that has solved the problem of how to live in a different way.”

This story is not about Mono Lake or arsenic, she said, but about “cracking open the door and finding that what we think are fixed constants of life are not.”

Dr. Wolfe-Simon and her colleagues publish their findings Friday in Science.

Gerald Joyce, a chemist and molecular biologist at the Scripps Research Institute in La Jolla, Calif., said the work “shows in principle that you could have a different form of life,” but noted that even these bacteria are affixed to the same tree of life as the rest of us, like the extremophiles that exist in ocean vents.

“It’s a really nice story about adaptability of our life form,” he said. “It gives food for thought about what might be possible in another world.

Phosphorus is one of six chemical elements that have long been thought to be essential for all Life As We Know It. The others are carbon, oxygen, nitrogen, hydrogen and sulfur.

While nature has been able to engineer substitutes for some of the other elements that exist in trace amounts for specialized purposes — like iron to carry oxygen — until now there has been no substitute for the basic six elements. Now, scientists say, these results will stimulate a lot of work on what other chemical replacements might be possible. The most fabled, much loved by science fiction authors but not ever established, is the substitution of silicon for carbon.

Phosphorus chains form the backbone of DNA and its chemical bonds, particularly in a molecule known as adenosine triphosphate, the principal means by which biological creatures store energy. “It’s like a little battery that carries chemical energy within cells,” said Dr. Scharf. So important are these “batteries,” Dr. Scharf said, that the temperature at which they dissolve, about 160 Celsius (320 Fahrenheit), is considered the high-temperature limit for life.

Arsenic sits right beneath phosphorus in the periodic table of the elements and shares many of its chemical properties. Indeed, that chemical closeness is what makes it toxic, Dr. Wolfe-Simon said, allowing it to slip easily into a cell’s machinery where it then gums things up, like bad oil in a car engine.

A bacterium known as strain GFAJ-1 of the Halomonadaceae family of Gammaproteobacteria, proved to grow the best of the microbes from the lake, although not without changes from their normal development. The cells grown in the arsenic came out about 60 percent larger than cells grown with phosphorus, but with large, empty internal spaces.

By labeling the arsenic with radioactivity, the researchers were able to conclude that arsenic atoms had taken up position in the microbe’s DNA as well as in other molecules within it. Dr. Joyce, however, said that the experimenters had yet to provide a “smoking gun” that there was arsenic in the backbone of working DNA.

Despite this taste for arsenic, the authors also reported, the GFAJ-1 strain grew considerably better when provided with phosphorus, so in some ways they still prefer a phosphorus diet.

http://www.nytimes.com/2010/12/03/science/03arsenic.html?pagewanted=1&_r=1&partner=rss&emc=rss

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