New meteorite; a new one in Costa Rica (Introduction)

by David Turell , Friday, August 14, 2020, 05:45 (1563 days ago) @ David Turell

Landed last year and is big enough to be equal to the Murchison:

https://www.sciencemagazinedigital.org/sciencemagazine/14_august_2020/MobilePagedArticl...

"Last year, an unusual meteorite crashed in a Costa Rican rainforest. Rich in the building blocks of life, it has captivated collectors and researchers.

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"Aguas Zarcas, as the fragments would soon collectively be called, is a carbonaceous chondrite, a pristine remnant of the early Solar System. The vast majority of meteorites are lumps of stone or metal. But true to their name, carbonaceous chondrites are rich in carbon—and not just boring, inorganic carbon, but also organic molecules as complex as amino acids, the building blocks of proteins. They illustrate how chemical reactions in space give rise to complex precursors for life; some scientists even believe rocks like Aguas Zarcas gave life a nudge when they crashed into a barren Earth 4.5 billion years ago.

"From the beginning, the inky Aguas Zarcas resembled a legendary carbonaceous chondrite that exploded in 1969 over Murchison, an Australian cattle town. Geology students helped collect about 100 kilograms of Murchison, and a local postmaster mailed pieces of it to labs across the world. To date, scientists have recognized nearly 100 different amino acids in it, many used by organisms on Earth and many others rare or nonexistent in known life. Hundreds more amino acids have been inferred but not yet identified.

"Murchison also contained nucleobases, the building blocks of genetic molecules such as RNA, and in November 2019, researchers found a major component of RNA’s backbone: the sugar molecule ribose. This half-century parade of discoveries jump-started the nowflourishing field of astrobiology. “We’re not detecting life itself, but the components are all there,” says Daniel Glavin, an astrobiologist at NASA’s Goddard Space Flight Center. “I wouldn’t have a job without Murchison.”

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"Few papers have been published on the meteorite so far—but they are coming. At the Field Museum, Heck is analyzing an almost 2-kilogram piece, donated by a retired health care executive, to probe the time before the Solar System took shape. He says his team has found a handful of candidate grains of silicon carbide, likely specks of dust scattered by aging giant stars that were later swept up in the protosolar disk. If confirmed and dated, those grains could add to an emerging picture of galactic conditions in the distant past.

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"Looking close at isovaline, an amino acid that occurs in space but is almost never found in earthly life, the NASA team has uncovered hints of a deeper pattern. Amino acids can occur in two mirror-image molecular forms, differing like right and left hands. Chemical reactions have no preference for either form, so left alone, nature should produce half-and-half mixtures. But organisms on Earth seem to build themselves out of only left-handed amino acids.

"That bias could reflect a roll of the dice by the first life, a random choice that descendants preserved. Another theory, published in May, suggests the left-hand bias arose on Earth: After life emerged in a mix of mirrorimage forms, the radiation of cosmic ray showers in the atmosphere, which has its own inherent handedness, offered an evolutionary advantage to organisms with lefthanded proteins.

"But Aguas Zarcas has up to 15% more left-handed than right-handed isovaline, underscoring similar findings from Murchison and other carbonaceous chondrites. The persistent pattern suggests the lefty bias may have arisen in space. Perhaps, another camp argues, the polarized light from nearby stars imparted a slight bias to meteoritic organic molecules that was incorporated by life. “I think the meteorites are telling us the story that we were destined to evolve left hand–based protein life,” Glavin says."

Comment: It seems to be as important as the Murchison. But it will not tell us how life started