Theoretical origin of life: using metals (Introduction)

by David Turell , Thursday, March 31, 2016, 06:30 (3159 days ago) @ David Turell

Metal ions are part of lots of life's organic molecules. This article referring to these metals as the 'metalome' infers that life started because of them. Of course the organic hydrocarbons and other polymerizing molecules are not given a source. No reference as to where they came from:-http://nautil.us/issue/34/adaptation/the-classic-metal-behind-the-origins-of-life-"Consider the history of iron, one of the metals of the metallome. The early ocean was dominated by iron atoms that were doubly positive charged ions (Fe2+). They were highly soluble in water, and therefore available as a “nutrient” that could be used for essential catalytic functions by oceanic life, like single-cell cyanobacteria.-"The iron was useful in more ways than one. These early lifeforms consumed carbon dioxide and sunlight to produce complex organic hydrocarbon molecules, and, as a byproduct, oxygen. Unfortunately, this oxygen was toxic to them. This is where the iron ions again came in handy: They scavenged toxic oxygen exhaled by the cyanobacteria into ocean water through an electron exchange process that produced triply charged iron atoms (Fe3+), and chemical species containing oxygen. -***-"The metallome didn't just help early life to perform its basic functions—it also helped it adapt to a changing Earth. Around 2 billion years ago, the Earth experienced a Great Oxidation Event (GOE). The photosynthetic bacteria population grew enough to produce oceanic oxygen at a level high enough for it to escape into the atmosphere.-"This was a pivotal event: The composition of the atmosphere changed dramatically as oxygen levels rose to near-modern levels. These high levels in turn increased the rate at which soluble Fe2+ was oxidized to insoluble Fe3+, but it also increased the rate at which ocean insoluble metallic sulfide salts (metals bound to sulfur) were oxidized to produce soluble sulfate salts (metals bound to sulfur and oxygen). As bio-available iron levels decreased, the availability of copper, zinc, and molybdenum all increased, as their salts became soluble.-***-"The composition of the atmosphere changed dramatically as oxygen levels rose to near-modern levels. These high levels in turn increased the rate at which soluble Fe2+ was oxidized to insoluble Fe3+, but it also increased the rate at which ocean insoluble metallic sulfide salts (metals bound to sulfur) were oxidized to produce soluble sulfate salts (metals bound to sulfur and oxygen). As bio-available iron levels decreased, the availability of copper, zinc, and molybdenum all increased, as their salts became soluble.-"This led to a host of changes in cellular chemistry. Where oceanic life had used tungsten as an oxygen atom transfer catalyst, it began to use molybdenum, which is actually a more efficient catalyst, but had been trapped in an insoluble form. The GOE also reduced oceanic iron concentrations, by transforming soluble iron (Fe2+) to insoluble iron oxide (Fe2O3). So cells adapted by putting an organic molecule coating on the surface of its iron ions, preventing them from being hydrated by water and precipitating out of the ocean as an oxide rock. -***-"The energy required to drive cyclic chemical reactions that are self-replicating—what we might call “life”—could come from reactions of the metallic elements. Our search for extraterrestrial life shouldn't be restricted to a search for remnants of complex organic molecules. There's another clear target, with a rather appropriately sci-fi ring to it: Heavy metals in space."-Comment: To be fair, the author is correct that metal/oxygen reactions and other metal reactions can provide energy for life and still do with metal eating bacteria, but it is the title of the article that should be changed to "After life appeared, these metals helped".