We know a lot less about early Earth life than I’d thought:
Two decades ago [Schopf] … was investigating … 3.5-billion-year-old rocks that are among the oldest on Earth. In 1993, he announced that they contained 11 different types of “microfossil” that looked for all the world like modern photosynthesising cyanobacteria. … Other 3.5-billion-year-old Australian rocks contained rippling structures that looked like fossil stromatolites. … Astonishingly soon after our planet formed some 4.6 billion years ago, photosynthesising bacteria were widespread. This emerging consensus lasted only until 2002, when palaeontologist Martin Brasier of the University of Oxford unleashed a barrage of criticisms. …
New lines of evidence mean that the oldest undisputed signs of cyanobacteria are now fossils found in rocks from the Belcher Islands in northern Canada dating from just 2.1 billion years ago. … In this “great oxygenation event” of around 2.4 billion years ago, levels rose from around 1 per cent of today’s levels to perhaps 10 per cent. Our best guess is still that cyanobacteria were around some time before this event. Persuasive evidence is converging on a date around 2.7 billion years ago. … The modern nitrogen cycle kicked off around this time. … The great oxygenation event … seems to have been the forerunner to a “snowball Earth”…. And yet the great oxygenation was impermanent. … By 1.9 billion years ago, levels of breathable oxygen in Earth’s atmosphere were back down to the merest trace. We don’t know why. …
Oxygen levels in the atmosphere soon recovered again … [at] a new equilibrium, at about 10 per cent of present-day levels. …. This time, the oxidative weathering of sulphides on land filled the oceans with sulphate. That in turn fuelled a hardy group of bacteria that … [turned oceans] into stinking, stagnant waters almost entirely devoid of oxygen. … An extraordinary stasis in Earth’s environment … dubbed the “boring billion” [years followed]. … What happened to the oxygenic utopia in which life supposedly grew and prospered, evolving the complex cells that went on to make up animal and plant life? … It probably never existed. … [Those] stinking oceans were the true cradle of life. Evidence behind this idea includes the fact that mitochondria, the powerhouses of all complex, oxygen-respiring “eukaryotic” cells today, were once far more varied, sometimes “breathing” sulphur or nitrogen instead of oxygen. ….
Earth’s anoxic stasis was broken in the end by a dramatic series of snowball Earths, indicating bursts of oxygen, beginning about 750 million years ago and recurring over the following 100 million years. They broke the eternal loop: soon afterwards, oxygen levels shot up and never looked back. Animal life soon exploded onto the scene. What made the difference this time? One intriguing possibility is that it was down to the organisms that had evolved in a leisurely way during the boring billion: terrestrial red and green algae and the first lichens.
More here. This will clearly require a rethinking of my hard steps of life analysis based a now outdated event timeline.
Now this is just weird: the Zodiac, an apparent ring of distinct extra bright stars centered on us, is not an illusion – it really exists out there. Called Gould’s belt, it is ~1000pc (parsec) in diameter, we are about 100pc of its center, and it formed together 30-60 million years ago:
Some think it formed when a clump of dark matter, massing about ten million suns, passed through a molecular cloud, an event they say should happen every ~300 million years. (Clumps pass elsewhere more often – Smith’s cloud, massing a hundred million suns, is passing right now. There should be about a thousand such clumps near our galaxy.)
Since our galaxy’s diameter is about 40,000pc , the chance that the most recent clump would hit that close to us was roughly one in (40,000/200)2, or one in 40,000. Since about a tenth of galaxy area has molecular clouds, the chance the most recent clump to hit a cloud would hit that close to us is one in 4000. Coincidence? Consider this plot from Jerison:
This dark matter clump hit us just about when the last big burst of max brain size growth began on Earth, with primates ~50 million years ago. Yes, it is hard to see how a rare dark matter clump passing near could induce a primate brain growth spurt, so it is probably coincidence. But big apparent coincidences should at least make us pause and ponder.
More details: Continue Reading "Cosmic Clump Coincidence?" »
New Scientist:
It’s arguably the most scrutinised piece of rock ever. Now an even closer look at a meteorite from Mars suggests it may show signs of life after all. …
One area of disagreement centred around nanocrystal magnetites in the rock, some of which appear to have chemical and physical features identical to those produced by contemporary bacteria. Sceptics of the biological explanation suggested that the magnetites were created when carbonate decomposed under high pressures and temperatures, …
Now a fresh analysis by McKay and colleagues rules out the carbonate decomposition explanation. … The possibility that the rock contains fossilised microbes received another boost in August when a team … showed that carbon in the meteorite was deposited in balmy water conducive to life.
Of course this doesn’t directly confirm longer distance panspermia.
Over the last few days I’ve neglected my duties to obsessively browse the last seven years of three journals: Astrobiology, International Journal of Astrobiology, and Origins of Life. In the process I’ve become converted to a more expansive version panspermia – life here probably originated outside our solar system. I’ve also learned: panspermia is no longer a marginalized view. It may not yet be the majority opinion, but it shows up often in journal articles and conference proceedings, if not in summaries intended for wider audiences.
My interest in panspermia over the years was probably heightened by my sense that it seemed more believable than its apparent outcast status suggested – I may have hoped for the glory of being an early supporter of a crazy-seeming view that eventually became the consensus view. But that hope neglected the prospect that many other young researchers shared my opinion – I’d have to distinguish myself among all those folks to gain much glory.
Academia is often run by an old guard ensuring that its public face reflects their old views, while younger folk quietly bite their tongues waiting for their chance to shine. But just because you can see well enough to understand what those new generations will later say doesn’t mean you have much of an advantage competing with them – many of them, perhaps most, can see as well as you.
Long term prediction markets on academic questions could cut through this old guard deception. But someone would have to be offended enough by this deception to fund such markets, and I see little evidence of this. Most academic patrons just want to affiliate with the high status old guard, no matter what its views, and those who do care about particular views aren’t confident enough in them to risk supporting prediction markets that might not agree.
Versions of panspermia can be distinguished by how far/long life had to travel:
- Orbit and Back – Early bombardments of Earth may have kicked some life up into orbit, to fall back down and re-seed Earth after big bombardments killed life on Earth.
- Outer Solar System – Since the outer system cooled first, life had more time to evolve there, before some bombardment kicked life off it to Earth. Mars and Ceres are two possibilities.
- Comet Cloud – There is far far more water and clay a thousand AU out, it was all pretty warm long ago, and can long stay warm inside big comets.
- Sun’s Nursery – There was even more water and clay around the thousands of stars that mixed closely for 100My in the 1-3 parsec nebula where our Sun was born.
- Star Passing Cloud – In the galaxy’s main ring, every 50My each star comes within a few parsecs of a giant molecular cloud for a 3My period, and comet impacts kick life off planets in dust that takes ~100Ky to reach the giant cloud. Within 10-100My such clouds become star nurseries.
- Star to Star – Life that could survive for many millions of years could directly reach planets around distant stars.
This last version doesn’t look good, but the other ones seem feasible and likely.
William Napier was born in 1940 and got his Ph.D. three years after his B.S., in 1966. After a career as a professional astronomer, he published his first book of fiction in 1998, at the age of 58, and published three more over the next five years.
But I still would not have heard of Napier had I not read his two brilliant 2007 Astrobiology papers, published when he was 67. The first argued comets were a likely origin of life:
A single comet of radius 10 km … contains [about] as much clay … as … early Earth. … Our Solar System is surrounded by about 1011 comets … A cometary interior provides a stable, aqueous, organic-rich environment for around 106 years.
The second showed that life could spread across a galaxy when via giant molecular clouds reliably collecting life from the stars they drift near, and then passing that life on to a few of the thousands of new stars they create. I now honor Napier by quoting lots of his detail: Continue Reading "All Hail William Napier" »
In August I wrote:
A few years ago PCW Davies persuasively argued that Earth life more likely started on Mars. Last year, Napier and coauthors argued that comets are an even more likely source:
A single comet of radius 10 km and 30% volume fraction of clay contains as much clay, to within a factor of around 10, as that of the early Earth. However, our Solar System is surrounded by about 1011 comets forming the Oort cloud … Whereas the average persistence of shallow clay pools and hydrothermal vent concentrations of clay on the Earth can range from 1 to around 100 years, a cometary interior provides a stable, aqueous, organic-rich environment for around 106 years.
The larger the region from which life could plausibly have started and then come to Earth, the more likely Earth life becomes in that scenario, and the more believable is whatever theory suggested that scenario. The latest Scientific American suggests to me an even larger plausible region of orgin: life’s origin may go back to the tight warm mixing cluster of stars where the Sun formed. Simon Zwart: Continue Reading "A Galactic Garden" »
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A community of the bacteria Candidatus Desulforudis audaxviator has been discovered 2.8 kilometres beneath the surface of the Earth in fluid-filled cracks of the Mponeng goldmine in South Africa. Its 60C home is completely isolated from the rest of the world, and devoid of light and oxygen. …
99.9% of the DNA [there] belonged to one bacterium, a new species. The remaining DNA was contamination from the mine and the laboratory. … A community of a single species is almost unheard of in the microbial world. … Deep-sea vent communities, for instance … use oxygen … produced by photosynthesising plankton at the surface. ….
Continue Reading "Behold Our Ancestors" »
A few years ago PCW Davies persuasively argued that Earth life more likely started on Mars. Last year, Napier and coauthors argued that comets are an even more likely source:
The recognition that life has an information content too vast to be assembled by random processes has led to many discussions of possible evolutionary routes, starting from a simpler self-replicating organic system and ultimately leading to the present-day protein- DNA-based life. … The clay model … uses the repeating lattice structures of clay particles and their catalytic properties of converting simple organic molecules in aqueous solution into complex biopolymers. …
The volume of clay on the Earth is vastly surpassed by that in comets. A single comet of radius 10 km and 30% volume fraction of clay contains as much clay, to within a factor of around 10, as that of the early Earth. However, our Solar System is surrounded by about 10^11 comets forming the Oort cloud … Whereas the average persistence of shallow clay pools and hydrothermal vent concentrations of clay on the Earth can range from 1 to around 100 years, a cometary interior provides a stable, aqueous, organic-rich environment for around 10^6 years. … mechanisms for interstellar panspermia have recently been identified, and we may
have to multiply this number by the number of Oort cloud analogues in the Galaxy.
(See also comments.) The entire paper is very short and qualitative – I’d have preferred quantitative discussion of rates of comet collisions with each other and with early Earth, to help us estimate how fast comet life could spread across comets, and how far it would have needed to spread to give it a decent chance of spreading to Earth.
But my core reaction is to marvel at how little work like this gets done. Figuring out the origins of life usually comes near the top of important scientific questions, yet in fact few resources go into this area. One reason, I suspect, is that for now the best way to approach this subject is qualitative and integrative, while academia mainly rewards impressive displays of ways with words, math, and tech. Does the topic also just seem silly?
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