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Wikipedia:Reference desk/Archives/Science/2016 October 24

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October 24

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Biological Endothermic Processes 3E9 YA

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I have a question about what biological endothermic reactions were used by the anaerobic organisms to capture solar energy, which could then be utilized to provide energy, three billion years ago. I haven’t found the answer in the articles that I have read so far. Two billion years ago, the planet was not that different than it is today, and photosynthesis converted water and carbon dioxide into glucose with the release of diatomic oxygen. The development of photosynthesis by the cyanobacteria, approximately 2.5 billion years ago, resulted in the great oxygenation event or oxygen catastrophe, and aerobic life became dominant. What endothermic reactions captured solar energy, presumably with less captured energy, prior to photosynthesis? I am assuming that there were endothermic processes capturing solar energy, because otherwise life would have been running entirely on leftover energy. Were the early endothermic reactions inorganic? Regardless of whether they were organic or inorganic, do they still occur in the modern oxygen-based world? Robert McClenon (talk) 03:15, 24 October 2016 (UTC)[reply]

Your assumption is incorrect. Organisms at places such as hydrothermal vents are "running entirely on leftover energy". There is no rule that says life must ultimately derive its energy from the Sun. We've found extremophiles in many habitats without access to sunlight. This has excited a lot of people about the prospects for life elsewhere in the universe. A place like Europa might have life in the subsurface ocean even though there's no sunlight available. There's a lot of "leftover energy" beneath a planet or large moon's surface. (Although, a substantial portion of this energy is produced by radioactive decay, which might not count as "leftover" based on your definition.) --47.138.165.200 (talk) 08:00, 24 October 2016 (UTC)[reply]
Primary producers are generally divided between photoautotrophs, which rely on the sun, and chemoautotrophs that derive energy and growth by acting on inorganic chemicals present in the environment. Such compounds are abundant at locations like hydrothermal vents, but can be found in low quantities nearly everywhere. Many chemolithotrophs consume compounds derived from minerals exposed at the Earth's surface. Other chemotrophs consume compounds like methane, which was believed to be abundant in the pre-oxic atmosphere. Yet other chemotrophs can create methane by consuming carbon dioxide and hydrogen. There are many metabolic pathways capable of capturing energy from inorganic compounds. In general such pathways usually offer less abundant energy than photosynthesis, but many forms of life can survive without a connection to the sun. Dragons flight (talk) 09:48, 24 October 2016 (UTC)[reply]
I know about Europa and about life at hydrothermal vents. Let me restate the question. Are there processes, that would have existed three billion years ago and presumably still exist, that are photoautrophic and so capture energy from the sun, but do not produce diatomic oxygen, and may capture lesser quantities of energy than is captured by photosynthesis as we know it? Are there biological processes, probably less endothermic than photosynthesis, that do not result in oxygen? If there is life on Europa, the source of its energy is tidal flexing. The ultimate source of energy for life at hydrothermal vents is the heat in the Earth, which in turn is a result of tectonic processes and radioactivity in the Earth. The source of energy for most present-day life is the Sun; was the Sun a source of energy for life before the great oxygenation event? Robert McClenon (talk) 05:46, 25 October 2016 (UTC)[reply]
Anoxygenic photosynthesis? Dragons flight (talk) 11:39, 25 October 2016 (UTC)[reply]
A little sympathy is in order for the anaerobic bacteria. It was their planet once. Robert McClenon (talk) 03:15, 24 October 2016 (UTC)[reply]


So, let's clear this up: there is plenty of evidence for oxygenic autotrophic photosynthesis and even eukaryotes long before 2.5 Ga and the great oxygenation event: " Even at ca 3.2 Ga, thick and widespread kerogenous shales are consistent with aerobic photoautrophic marine plankton"[1]. This article says it "provides persuasive evidence for the existence of eukaryotes 500 million to 1 billion years before the extant fossil record indicates that the lineage arose." [2].
As for what was going on before oxygenic photosynthesis: This [3] paper may be a good read on the impact of anoxygenic photosynthesis. It is ostensibly focused on the proterozoic but touches upon the transition and has good refs.
My understanding is that there just wasn't much photosynthesis of any sort going on when you look long before the great oxygenation event. Our article doesn't exactly come out and say it, but it strongly implies a world dominated by methanogens, e.g. in the section "nickel famine".
Other info on life prior to Cyanobacteria#Earth_history can be found at Archean and Abiogenesis. SemanticMantis (talk) 14:37, 25 October 2016 (UTC)[reply]

Stimulated emission versus quantum encryption

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In a laser, stimulated emission seems to copy a photon in all regards with a second photon of the same type. This seems like a way of detecting a photon without intercepting it, because you could, say, look for further emissions from atoms that have dropped into a lower-energy (but not ground-energy) state as the result of intercepting a photon.

Suppose you have a quantum-entangled photon pass through an atom, stimulating emission of a second identical photon of that type. A moment later, the atom is subjected to a strong magnetic field, so that the polarization of the electron affects the subsequent emission as it drops further in state. Then you can find out the polarization of the photon (which I'll suppose carries an encrypted message). Does that let you eavesdrop on the secret message?

Bonus... actually, I was wondering if there's any way to use this to detect neutrinos without really stopping them. Wnt (talk) 16:34, 24 October 2016 (UTC)[reply]

This article goes into some of the relevant details of this problem. Count Iblis (talk) 20:41, 24 October 2016 (UTC)[reply]

Solar system Gas giants

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Banned user
The following discussion has been closed. Please do not modify it.

Although we call them gas giants, is it not true that they must have solid cores due to the gravitational forces acting?--213.205.252.244 (talk) 17:16, 24 October 2016 (UTC)[reply]

I believe that Jupiter, Saturn, Neptune, and Uranus are each expected to have a small solid core; however, I'm not sure a gas giant "must" have a solid core. The largest gas giants aren't that different from the smallest stars (red dwarfs) and I don't think any stars are expected to have solid cores. I'm not sure there is any reason that a gas cloud couldn't, in principle, collapse into a gas giant without having a solid core. Alternatively, if the core were hot enough, it need not be solid. So the set of possible gas giants may include some versions that don't have solid cores. Dragons flight (talk) 18:05, 24 October 2016 (UTC)[reply]
Those are sub-brown dwarfs. Sagittarian Milky Way (talk) 18:14, 24 October 2016 (UTC)[reply]
Jupiter#Internal structure, Saturn#Internal structure, Uranus#Internal structure, and Neptune#Internal structure all describe the current state of understanding of this subject. --Jayron32 19:49, 24 October 2016 (UTC)[reply]

Which article covers ViDAR?

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Visual Detection and Ranging

etc. Hcobb (talk) 23:15, 24 October 2016 (UTC)[reply]

There is no Wikipedia article about ViDAR. Such an article would need disambiguation from the existing article about Víðarr, a Norse God. One can propose covering ViDAR in the article Machine vision or including ViDAR in the Glossary of machine vision. AllBestFaith (talk) 23:30, 24 October 2016 (UTC)[reply]
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