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Minerals, Organics and Early Life

Where did our planet get the stuff from which life is made? The sources seem surprisingly diverse, and we’re learning more about how organic materials may have complemented each other in forming life four billion years ago. Extraterrestrial compounds — biomolecules formed in deep space and falling to Earth — probably contributed. And so did lightning and ultraviolet radiation, along with vulcanism and deep water chemical reactions that could enhance molecular synthesis.

Now getting new emphasis is the role of mineral surfaces in helping to activate molecules essential to life, like amino acids (from which proteins are made) and nucleic acids (think DNA). In a recent study, Robert Hazen (Carnegie Institution Geophysical Laboratory) described where we stand at identifying the pairing of molecule and mineral. When molecules like amino acids adhere to mineral surfaces, a variety of organic reactions can occur that affect what life can emerge.

“Some 20 different amino acids form life-essential proteins,” Hazen explained. “In a quirk of nature, amino acids come in two mirror-image forms, dubbed left and right-handed, or chiral molecules. Life, it turns out, uses the left-handed varieties almost exclusively. Non-biological processes, however, do not usually distinguish between left and right variants. For a transition to occur between the chemical and biological eras, some process had to separate and concentrate the left- and right-handed amino acids. This step, called chiral selection, is crucial to forming the molecules of life.”

The hunt, then, is to find what mineral surfaces are what Hazen calls the best ‘docking stations’ for various biomolecules. The possibilities are vast considering the number of mineral types and available molecules, but Hazen’s team is using DNA microarray technology to help. The result is to overhaul the protocols for doing this work and make the investigation both more accurate and much faster. The technique allows the team to study these complex interactions and discover which mineral surfaces and which organic molecules manage to work together.

Much work lies ahead, but Hazen’s team can now identify a million types of biomolecules through their interactions with mineral surfaces, and analyze the results quickly. The goal is an understanding of how specific organics from the vast number available assembled into early life, and how they were able to become concentrated enough to begin a basic metabolism. The work, which draws on biology, chemistry and geology, gives us a glimpse not only of the primitive Earth but a better understanding of the conditions that may lead to life on other worlds.

The paper is Hazen, “Mineral surfaces and the prebiotic selection and organization of biomolecules,” American Mineralogist Vol. 91, No. 11-12 (November, 2006), pp. 1715-1729.

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  • ljk February 22, 2008, 11:35

    An Extended Model for the Evolution of Prebiotic Homochirality: A Bottom-Up Approach to the Origin of Life

    Authors: Marcelo Gleiser, Sara Imari Walker

    (Submitted on 20 Feb 2008)

    Abstract: A generalized autocatalytic model for chiral polymerization is investigated in detail. Apart from enantiomeric cross-inhibition, the model allows for the autogenic (non-catalytic) formation of left and right-handed monomers from a substrate with reaction rates $\epsilon_L$ and $\epsilon_R$, respectively. The spatiotemporal evolution of the net chiral asymmetry is studied for models with several values of the maximum polymer length, N. For N=2, we study the validity of the adiabatic approximation often cited in the literature.

    We show that the approximation obtains the correct equilibrium values of the net chirality, but fails to reproduce the short time behavior. We show also that the autogenic term in the full N=2 model behaves as a control parameter in a chiral symmetry- breaking phase transition leading to full homochirality from racemic initial conditions. We study the dynamics of the N – greater than infinity model with symmetric ($\epsilon_L = \epsilon_R$) autogenic formation, showing that it only achieves homochirality for $\epsilon less than \epsilon_c$, where $\epsilon_c$ is an N-dependent critical value. For $\epsilon \leq \epsilon_c$ we investigate the behavior of models with several values of N, showing that the net chiral asymmetry grows as tanh(N).

    We show that for a given symmetric autogenic reaction rate, the net chirality and the concentrations of chirally pure polymers increase with the maximum polymer length in the model. We briefly discuss the consequences of our results for the development of homochirality in prebiotic Earth and possible experimental verification of our findings.

    Subjects: Biomolecules (q-bio.BM); Astrophysics (astro-ph); Chemical Physics (physics.chem-ph)

    Cite as: arXiv:0802.2884v1 [q-bio.BM]

    Submission history

    From: Sara Walker [view email]

    [v1] Wed, 20 Feb 2008 15:31:01 GMT (459kb,D)


  • ljk March 8, 2008, 15:00

    Indigenous amino acids in primitive CR meteorites

    Authors: Z.Martins, C.M.O’D.Alexander, G.E.Orzechowska, M.L.Fogel, P.Ehrenfreund

    (Submitted on 5 Mar 2008)

    Abstract: CR meteorites are among the most primitive meteorites. In this paper, we report the first measurements of amino acids in Antarctic CR meteorites, two of which show the highest amino acid concentrations ever found in a chondrite. EET92042, GRA95229 and GRO95577 were analyzed for their amino acid content using high performance liquid chromatography with UV fluorescence detection (HPLC-FD) and gas chromatographymass spectrometry (GC-MS).

    Our data show that EET92042 and GRA95229 are the most amino acid-rich chondrites ever analyzed, with total amino acid concentrations ranging from 180 parts-per-million (ppm) to 249 ppm. GRO95577, however, is depleted in amino acids.

    The most abundant amino acids present in the EET92042 and GRA95229 meteorites are the alpha-amino acids glycine, isovaline, alpha-aminoisobutyric acid (alpha-AIB), and alanine, with delta13C values ranging from +31.6per mil to +50.5per mil. The carbon isotope results together with racemic enantiomeric ratios determined for most amino acids strongly indicate an extraterrestrial origin of these compounds. In addition, the relative abundances of alpha-AIB and beta-alanine in the Antarctic CR meteorites analyzed appear to correspond to the degree of aqueous alteration on their respective parent body.

    Comments: Meteoritics and Planetary Science, in press

    Subjects: Astrophysics (astro-ph)

    Cite as: arXiv:0803.0743v1 [astro-ph]

    Submission history

    From: Zita Martins [view email]

    [v1] Wed, 5 Mar 2008 21:01:35 GMT (383kb)


  • ljk October 21, 2008, 10:23


    October 20, 2008

    Did Lightning and Volcanoes Spark Life on Earth?

    Written by Nancy Atkinson

    Chilean Volcano in 2008 creates lightning. Credit: AP

    Maybe the fictional Dr. Frankenstein wasn’t so crazy after all. Two scientists have resurrected an old experiment, breathing life into a “dead” notion about how life began on our planet. New analysis shows that lightning and gases from volcanic eruptions could have given rise to the first life on Earth.

    “It’s alive!”…

    Back in the early 1950s, two chemists Stanley Miller and Harold Urey of the University of Chicago did an experiment that tried to recreate the conditions of a young Earth to see how the building blocks of life could have arisen. They used a closed loop of glass chambers and tubes with water and different mixes of hydrogen, ammonia, and methane; the gases thought to be in Earth’s atmosphere billions of years ago. Then they zapped the mixture with an electrical current, to try and confirm a hypothesis that lightning may have triggered the origin of life. After a few days, the mixture turned brown.

    When Miller analyzed the water, he found it contained amino acids, which are the building blocks of proteins — life’s toolkit. The spark provided the energy for the molecules to recombine into amino acids, which rained out into the water. The experiment showed how simple molecules could be assembled into the more complex molecules necessary for life by natural processes, like lightning in Earth’s primordial atmosphere.

    But there was a problem. Theoretical models and analyses of ancient rocks eventually convinced scientists that Earth’s earliest atmosphere was not rich in hydrogen, so many researchers thought the experiment wasn’t an accurate re-creation of early Earth. But the experiments performed by Miller and Urey were ground-breaking.

    “Historically, you don’t get many experiments that might be more famous than these; they re-defined our thoughts on the origin of life and showed unequivocally that the fundamental building blocks of life could be derived from natural processes,” said Adam Johnson, a graduate student with the NASA Astrobiology Institute team at Indiana University, Bloomington. Johnson is the lead author on a paper that resurrects the old origin-of-life experiments, with some tantalizing new findings.

    Miller died in 2007. Two former graduate students of Miller’s –geochemists Jim Cleaves of the Carnegie Institution of Washington (CIW) in Washington, D.C., and Jeffrey Bada of Indiana University, Bloomington–were examining samples left in Miller’s lab. They found the vials of products from the original experiment and decided to take a second look with updated technology. Using extremely sensitive mass spectrometers at NASA’s Goddard Space Flight Center Cleaves, Bada, Johnson and colleagues found traces of 22 amino acids in the experimental residues. That is about double the number originally reported by Miller and Urey and includes all of the 20 amino acids found in living things.

    Miller actually ran three slightly different experiments, one of which injected steam into the gas to simulate conditions in the cloud of an erupting volcano. “We found that in comparison to Miller’s classic design everyone is familiar with from textbooks, samples from the volcanic apparatus produced a wider variety of compounds,” said Bada.

    This is significant because thinking on the composition of Earth’s early atmosphere has changed. Instead of being heavily laden with hydrogen, methane, and ammonia, many scientists now believe Earth’s ancient atmosphere was mostly carbon dioxide, carbon monoxide, and nitrogen. But volcanoes were active during this time period, and volcanoes produce lightning since collisions between volcanic ash and ice particles generate electric charge. The organic precursors for life could have been produced locally in tidal pools around volcanic islands, even if hydrogen, methane, and ammonia were scarce in the global atmosphere.

    So, this breathes life into the notion of lightning jump-starting life on Earth. Although Earth’s primordial atmosphere was not hydrogen-rich, gas clouds from volcanic eruptions did contain the right combination of molecules. Is it possible that volcanoes seeded our planet with life’s ingredients? While no one knows what happened next, the researchers are continuing their experiments in an attempt to determine if volcanoes and lightning are the reasons we’re here.

    The paper was published in Science on Oct. 17, 2008