One of the building blocks of life has been found on a comet hurtling through the solar system, adding evidence to the theory that earthly biology began when comets and meteors bombarded our young planet and seeded it with the precursors of life. The amino acid, glycine, was found in a sample returned by the space probe Stardust that buzzed by the comet Wild 2 in 2004. The probe swept up particles fizzing off the object’s surface as it passed some 240km (149 miles) from the comet’s core, or nucleus. These tiny grains, just a few thousandths or a millimetre in size, were then returned to Earth in 2006 in a sealed capsule [BBC News].
Amino acids are crucial to life because they form the basis of proteins, the molecules that run cells. The acids form when organic, carbon-containing compounds and water are zapped with a source of energy, such as photons – a process that can take place on Earth or in space [New Scientist].
(more…)
How life evolved from a mix of chemicals on the young planet Earth is one of science’s most enduring mysteries, which biochemists are attempting to solve by recreating the earliest building blocks of life in the laboratory.
Earth’s biology is based on DNA, which carries all an organism’s genetic information in a molecule that takes the shape of a spiraling ladder. RNA, the molecule that facilitates protein manufacturing, has a simpler shape–it’s a single strand, as opposed to DNA’s double strand–leading some biologists to propose the RNA world hypothesis in which RNA evolved first and eventually gave rise to DNA. But trying to imagine the assembly of RNA from its chemical components poses its own problems. How could RNA, which encodes proteins, first form, when proteins are needed for [its] synthesis? Now, scientists report that they’ve cooked up molecular hybrids of proteins and nucleic acids that skirt the dreaded paradox [ScienceNOW Daily News].
The hybrids they created could resemble the precursors to RNA, researchers report in Science. “It’s the pre-RNA world. There’s a hypothesis that says RNA is so complicated, it couldn’t have arisen de novo” — from scratch — “on early Earth,” said study co-author Luke Leman…. “So you need some more primitive genetic system that nature fiddled around with and finally decided to evolve into RNA” [Wired.com].
(more…)
Left-handed people may be in the minority, but left-handed amino acids rule the Earth. Researchers have long known that the building blocks of proteins can be constructed in either “left-handed” or “right-handed” versions that are mirror images of each other, but that almost every living organism on Earth uses left-handed amino acids. Now, a new study gives weight to a theory of how that preference came to pass. NASA researchers examined meteorites that predate the Earth’s formation, and say that those early rocks also have a preponderance of left-handed molecules. “Meteorites would have seeded the Earth with some of the prebiotic compounds like amino acids that are needed to get life started, and also biased the origin of life to the left-handed amino acid form,” says [study coauthor] Daniel Glavin [New Scientist].
Researchers note that if you make amino acids from scratch in a lab using their chemical components, you inevitably get half of the right-handed version and half of the left handed version. So it might be expected that if nature makes amino acids in space using similar chemistry, you’d also get a fifty-fifty mixture [CBC]. Yet that’s not what Glavin and his colleagues found when they studied the molecular deposits in six meteorites that are more than 4.5 billion years old. Instead, they found the ratio of amino acids tilted toward left-handedness in all six specimens. In one of the rocks, the imbalance was 18%, the largest ever reported for a meteorite. “I have to admit I didn’t believe it at first,” Glavin says [ScienceNOW Daily News].
(more…)
By tweaking chemical strands of RNA, researchers have taken another step towards understanding how life may have first evolved on our planet. A test tube based system of chemicals that exhibit life-like qualities such as indefinite self-replication, mutation, and survival of the fittest, has been created by US scientists…. “This is the very end of the line, where chemistry starts turning into biology” [Chemistry World], says researcher Gerald Joyce. Researchers have previously created RNA strands that replicated themselves for a while before grinding to a halt, but this experiment marks the first creation of RNA strands that continue to replicate themselves indefinitely, which set up the conditions that allowed for evolution.
In the modern world, DNA carries the genetic sequence for advanced organisms, while RNA is dependent on DNA for performing its roles such as building proteins. But one prominent theory about the origins of life, called the RNA World model, postulates that because RNA can function as both a gene and an enzyme, RNA might have come before DNA and protein and acted as the ancestral molecule of life [Astrobiology Magazine].
(more…)
Over 4 billion years ago the young and barren Earth was being buffeted by meteor strikes, and that violent bombardment could have created the first amino acids that then gave rise to the origin of life on the planet, a new study suggests. The hellish temperatures and pressures generated when an extraterrestrial object strikes Earth at speeds of several kilometers per second are enough to shatter and vaporize rock…. Yet part of such an immense burst of energy can trigger chemical reactions that generate complex organic substances from basic inorganic ingredients, says Takeshi Kakegawa [Science News].
Previously, researchers have suggested that organic molecules may have been created elsewhere in the universe and were brought to Earth by meteors. But the new study, in which researchers simulated the impact of meteorites in the primordial ocean, argues that the organic molecules could have been synthesized from the inorganic molecules already present on the planet when the meteorites crashed into the ocean. Other researchers have suggested similar processes for the creation of organic molecules on Earth, including lightning strikes or chemical reactions surrounding hot, volcanic vents in the deep sea.
(more…)
The evolution of minerals on our planet has been propelled by the evolution of life on earth, a sweeping new study demonstrates. While the underlying assumption isn’t new, the study is the first to chart how the emergence of algae and then complex microorganisms gave rise to the 4,300 or so minerals that are now present on earth.
In the early days of the universe, clouds of gas and dust contained all the naturally occurring elements found in the periodic table, but most were too widely dispersed to form minerals; scientists believe there were only about a dozen minerals in the interstellar medium. According to the study, around a further 60 different minerals formed 4.5 billion years ago, as clumps of matter collided and coalesced to begin forming the Solar System. The smaller fragments congealed into larger, planet-sized bodies, where volcanism and the effects of water took the mineral count into the hundreds. The planets Mars and Venus have got this far [Nature News], and have minerals created by hot magma like quartz and zircon.
(more…)
Vials holding the results of a famous chemistry experiment conducted 55 years ago have been discovered in dusty cardboard boxes, and a new analysis of their contents has revealed fresh insights into a big question: the origin of life on earth. In 1953, chemist Stanley Miller tried to duplicate the conditions present on the primordial earth in laboratory flasks, and while some of his results were published to great acclaim, other results were packed away and forgotten–until now.
Miller’s classic experiment involved putting atmospheric components thought to reflect those of the early Earth (ammonia, hydrogen, methane, and water) in a closed system and stimulating that mixture with an electric current to mimic the effects of lightning storms. He generated a small number of biochemically significant compounds, including amino acids, hydroxy acids, and urea, showing that conditions of primitive earth can create the building blocks of life [Ars Technica]. These results generated considerable excitement, but later researchers argued that Miller was wrong about the composition of the young earth’s atmosphere, and the experiment was written off as a novelty.
(more…)
In a salty hot spring near Mono Lake, California, researchers have found two new species of bacteria that use arsenic for photosynthesis, and require no oxygen to fuel the process. Researchers say the bacteria may be similar to those that existed on primordial Earth where oxygen was scarce, and may illustrate an important stage of how early life developed in mineral-rich waters over 2 billion years ago.
Arsenic is well-known for its toxicity; it was used so often as tool for homicide in the 1800s that it earned the nickname “king of poisons” [The Scientist]. Yet the newly discovered bacteria can not only tolerate the element, they require it to survive. One of the first steps most organisms perform in photosynthesis is to split water molecules, creating oxygen. Oxygen donates energy in the form of electrons to other molecules, setting off a chain reaction that eventually results in the building of sugars for the organism’s own food. For the red and green bacteria found in Mono Lake, arsenic plays the role of oxygen [Science News].
(more…)
Researchers say that diamond fragments from the dawn of time may contain evidence that life began on Earth as early as 4.25 billion years ago, just a few hundred million years after the planet came into existence–although they also say that their findings aren’t conclusive and that they may well be wrong.
Studying anything about the ancient earth is extremely difficult. Rocks that formed four billion years ago will long since have been beat up, metamorphosed, or melted [Nobel Intent blog, Ars Technica]. Researchers got around that problem by studying microscopic diamond pieces inside zircon crystals, which are themselves the tough remnants of ancient rocks that have long since disappeared. “We don’t have the rocks. These zircons are just little fragments of something that was broken up, weathered and redeposited as sediments,” explained [coauthor Martin] Whitehouse [BBC News].
(more…)
