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August 19, 2011 10:11 pm
Powerful new evidence that the building blocks of life on earth arrived from space has emerged from a new analysis of meteorites by scientists working for Nasa.
The most important chemicals in biology are proteins, which are made of units called amino acids, and the genetic molecules DNA and RNA, which are constructed from building blocks called nucleobases.
The existence of amino acids in space has already been proved by the analysis of meteorites that have struck earth, and comet samples collected in space during Nasa’s Stardust mission. It has been harder to prove that traces of nucleobases found in meteorites were not the result of contamination after they arrived – but the new study seems to do so, while showing that nucleobases reach earth from space in greater diversity and quantity than scientists had thought.
The Nasa team analysed samples of 12 carbon-rich meteorites, including nine found in Antarctica (a rich collecting ground), and detected guanine and adenine, two of the four nucleobases that make up DNA. They also found three related molecules known as nucleobase analogues, a discovery which provides confirmation that the organic compounds in meteorites come from space.
“You would not expect to see these nucleobase analogues if contamination from terrestrial life was the source, because they’re not used in biology,” says Michael Callahan, lead author of the study, which appears in Proceedings of the National Academy of Sciences. “However, if asteroids are cranking out prebiotic material, you would expect them to produce many variants of nucleobases, not just the biological ones, because of the wide variety of ingredients and conditions in each asteroid.”
Further confirmation came from an analysis of Antarctic ice, taken from near where the meteorites were collected, which showed no trace of the compounds.
The team then carried out lab experiments to see whether nucleobases and their analogues could be generated by the chemical reaction of ammonia and cyanide, two very simple molecules that are common in space.
“In the lab, an identical suite of nucleobases and analogues were generated in non-biological chemical reactions containing hydrogen cyanide, ammonia and water. This provides a plausible mechanism for their synthesis in the asteroid parent bodies, and supports the notion that they are extraterrestrial,” says Callahan.
While previous claims by Nasa scientists to have found fossils of tiny microbes in meteorites remain controversial, no one is likely to dispute this discovery that life’s biochemical building blocks arrived from space. How they combined on earth to form the first primitive organisms remains a mystery.
Why chimps go ape for altruism
Biologists who study chimpanzees in the wild are often struck by their displays of empathy, generosity and altruism towards other members of their group. But formal tests with captive chimps have generally failed to show this sort of “prosocial” behaviour, leading some scientists to suspect that human altruism has evolved over the six million years since our ancestors split from the apes.
Now, a US study at the Yerkes Primate Research Centre, the world’s leading laboratory for chimpanzee research, has demonstrated that chimps do choose generosity over selfishness.
Frans de Waal, senior Yerkes researcher, says previous studies were too intricate in the ways they attempted to study chimp altruism. “I have always been sceptical over the previous negative findings,” he says. “This study confirms the prosocial nature of chimpanzees with a different test, [one] better adapted to the species.”
The new study, published in Proceedings of the National Academy of Sciences, had a much simpler test. Seven female chimps, who had been trained to exchange coloured tokens for food, took part. One ape, the active “chooser”, could decide whether to select a token that delivered a treat just for her, or an alternative token that also yielded a treat for her partner.
All seven chimps showed an overwhelming preference for sharing over selfishness. And they were more generous to fellow chimps who waited silently, or quietly drew attention to themselves, than to noisier partners who made a fuss, begged insistently, or spat water at the chooser.
However, although the Yerkes researchers talk about “altruism”, the chooser chimp does not suffer herself in this study if she also obtains a treat for her partner. Still, it is good to know that chimps prefer to be nice than nasty.
Underwater volcanos: go with the (lava) flow
American volcanologists have made what they claim is the first successful prediction of an undersea eruption.
Bill Chadwick of Oregon State University and Scott Nooner of Columbia University, New York, published a scientific paper in 2006 stating that Axial Seamount, a subsea volcano located 480km off the coast of Oregon, would erupt before 2014.
And sure enough, when they visited the area at the end of July, a robotic submarine sent down to inspect the ocean floor found a large lava flow that had not been there on their previous visit last year.
“When we first arrived on the seafloor, we thought we were in the wrong place, because it looked so completely different,” says Chadwick. “We couldn’t find our markers or monitoring instruments or other distinctive features on the bottom. Once we figured out that an eruption had happened, we were pretty excited.”
Their prediction was based on the gradual swelling of the volcano, which was intensively monitored with sensors. Its surface had been rising by 15cm per year, as magma (molten rock) flowed in from beneath the earth’s crust.
“We now have evidence that Axial Seamount behaves in a more predictable way than many other volcanoes,” says Nooner. This is probably due to the volcano’s robust magma supply, coupled with its thin crust and location on a mid-ocean ridge, where the crust is constantly spreading.
The next test will be to see if the scientists can successfully forecast the next eruption, by measuring how fast the volcano swells over the next few years.
IVF breakthrough in embryo choice
Researchers at Cambridge University have found a new way of predicting whether a newly fertilised embryo is likely to implant and grow successfully during IVF treatment. Their technique was developed by studying mice, but they expect it to work with human embryos too.
The key discovery is that fertilisation of a mammalian egg initiates a series of pulsating movements in the cytoplasm, the jelly-like substance that fills the cell, which can be followed by a video-microscope.
By relating the frequency of the cytoplasm movements to the subsequent growth of the mouse embryos, the Cambridge researchers developed a mathematical model that predicts embryonic viability on the basis of pulsations in a newly fertilised egg. The study appears in the journal Nature Communications.
Since similar movements occur in newly fertilised human eggs, the scientists hope to apply the technique to enable IVF clinics to choose the best embryos for implantation in the womb, as soon after fertilisation as possible.
“It is important to be able to quantify some indication of the health of embryos at the earliest possible stage, in order to minimise the time they have to spend outside the body of the mother,” says Magdalena Zernicka-Goetz, the project leader.
The family way
Teenage pregnancy tends to be “contagious” within families, because girls are influenced by older sisters who have babies while young, according to a study of 42,000 Norwegian women.
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