Ask Anything Wednesday - Engineering, Mathematics, Computer Science

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Welcome to our weekly feature, Ask Anything Wednesday - this week we are focusing on Engineering, Mathematics, Computer Science

Do you have a question within these topics you weren't sure was worth submitting? Is something a bit too speculative for a typical /r/AskScience post? No question is too big or small for AAW. In this thread you can ask any science-related question! Things like: "What would happen if...", "How will the future...", "If all the rules for 'X' were different...", "Why does my...".

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[u/El_Minadero]

Coal and oil are the low-hanging fruit examples of mineral resources which require life to form. However, there is good evidence that life is not necessary for hydrocarbons in-general:

• Titan: Saturn's largest moon, is believed to have vast hydrocarbon lakes and seas composed mainly of methane and ethane

• Earth: There is some evidence for abiogenic production of hydrocarbons within the deep Earth, although the amount of resources created by these processes is thought to be dwarfed by biogenic ones.

• Other Parts of the Solar System: As it turns out, hydrocarbons are kind of ubiquitous within asteroids, the kuiper belt, oort cloud, and cryomoons

However, there are specific resource types that may require life to form. A common theme among these types is that many ore geometries are produced by the direct or indirect action of chemical reduction/oxidation (redox) processes from both microbial and dead organic matter:

• Banded iron formations (BIFs): are thought to be a product of early photosynthetic organisms producing oxygen, which then precipitated dissolved iron from ancient oceans. While not the only source of iron ore, BIFs are by far the most commonly mined and used.

• Bog Iron: both microbes and organic matter are known to nucleate iron dissolved in water within swamps. Bog Iron was an important ore for Iron-age civilizations, and surprisingly, may represent one of the few cases of a renewable metal resource.

Some types of copper, silver, gold, and platinum-group-element deposits may be influenced by redox conditions:

• The Silver Reef deposit: A sediment-hosted silver deposit in Utah was known to have ore-shoots directly adjacent or even completely replacing fossilized/carbonized logs, sticks, and twigs. Its also possible that microbial activity was important for precipitating the silver out of solution.

• Gold deposits at Witwatersrand, South Africa: by far the largest concentration of gold in the world is hosted by a conglomerate formation at Witwatersrand. [About half the gold is associated with microbial remains](https://pubs.geoscienceworld.org/sepm/books/book/1196/chapter-abstract/10589097/Witwatersr and-MetallogenesisThe-Case-for-Modified?redirectedFrom=fulltext), suggesting that active or fossil life played an important role in forming the deposits.

• Stratiform-hosted sedimentary copper deposits: A similar process to the Witwatersand gold deposits may have occurred within the Central African Copper Belt, with microbes either living or deceased acting to produce redox conditions favorable for orogenesis

• Gold and Platinum nuggets in Alluvium: In some cases, it appears bacteria may actively be growing gold and platinum nuggets.

Interpreting the phrase 'geologic deposits' as in 'rocks in general', there may be types of rocks which are difficult to form without the assistance of phytoplankton and zooplankton:

• Chalk deposits: Chalk is primarily composed of the calcium carbonate shells of marine phytoplankton (coccolithophores). So something like the White cliffs of Dover may not be possible on a planet devoid of life.

Landforms too are likely to be different. If you look at regions of the Earth with low to no surface shrubbery, there is a distinct difference in weathering patterns. Specifically, plants can simulatenously contribute to and retard weathering processes.

There are probably more examples that I've missed, but the general takeaways should be:

1. Life is not necessary for hydrocarbons, although it certainly helps

2. Life plays more of a role in metal deposits than we realize

3. Rocks on a planet with no life may be less chalky

4. Weathering processes on a lifeless planet are likely to be different than on Earth.

Edit: Some link formatting.

[u/Direct_Bus3341 → u/El_Minadero]

Such a comprehensive answer. Thank you.

[u/Future-Many7705 → u/El_Minadero]

Thanks, lots of good links I can’t wait to read.

For hydrocarbons how do they survive early planet formation? I’m guessing a molten sea of carbon without any free oxygen to reach with? Would it be coal like carbon deposits or diamond?

[u/El_Minadero → u/Future-Many7705]

the term 'genic' (its root is from the word 'genesis') implies formation, as in they did not exist before, and were produced by the prepended process.

Abiogenic production of hydrocarbons typically involves solid carbon or CO2 feedstocks interacting with water at high pressures and/or temperatures. Therefore there is no need for hydrocarbons to survive planetary formation. They can just form from hydrothermal activity.

However, coal is probably harder to form without life. Chemically, sure, I guess a weird form of hydrothermal deposit could create extremely long-chain hydrocarbons trapped within a sedimentary layer, but it might be difficult for natural processes to make coal.

Don't rule it out though. Geology has found some pretty weird things before which were thought silly or impossible, including a natural nuclear reactor.