How does life happen when there's barely any light?
quantamagazine.org
quantamagazine.org
That's why after mass extinction events, we see explosions in evolution in creatures that had essentially stagnated. Mammals being the best example of this. They went from being small little creatures with little distinction for generations to everything from a mouse to a mammoth. It wasn't until the rapid extinction of the dinosaurs with all the environmental gaps that created that we saw an explosion of different creature types. There were niches to fill.
This is likely part of the reason we see life in such extreme conditions. There was a hole to fill and the creatures best suited to survive in that niche did.
In a similar way to how the solution to inflation is higher prices, it may turn out to be a self righting process.
Also that this part of the galaxy, and the Universe as a whole, seems to be favourably quiescent.
Slightly tangential, have you come across the terms island dwarfism and island gigantism (also insular -), and did you know the New Zealand Kiwi is the T-Rex’s closest living genetic relative. Here’s hoping it never makes it off the island!
It's no wonder that Darwin started thinking "what's happening here" after visiting a bunch of islands.
My favorite island creature is the cold blooded dwarf goat Myotragus balearicus. Likely a victim of human expansion.
Sure it was cold blooded? Wikipedia claims it was a mammal.
The goat bones have a growth pattern only found in reptiles suggesting it had adapted to varying availability of food. Other morpholigic changes (smaller brain, smaller eyes) also suggest that it had at a minimum evolved to withstand low nutrition periods.
The working theory to these observed structures is that this mammal a rare example of a warm blooded creature turning cold blooded.
Stranger things have happened though, the evolutionary path of whales is particularly strange.
I was so excited to read about this, but it turns out further research found that all ruminants possess these structures:
https://www.nature.com/articles/nature11264
> Our study supplies the strongest evidence so far that homeothermic endotherms arrest growth seasonally, which precludes the use of lines of arrested growth as an argument in support of ectothermy.
The neat thing about this goat is how it now is part of a body of evidence that dinosaurs were endotherms.
But certainly it's not proven. These goats went extinct at something like 1000 BCE
Just pointing out strange fact of accelerated evolution after mass extinction. There are limits to what earth chemistry will allow for in life, and likely earth's climate and temperatures have been particularly hospitable to life forming and propagating.
On the low end, we're pretty much limited by the same things, but in reverse- the freezing point of water, and the fact that chemistry slows down at low temperatures.
So that puts us with a fundamental limit of 0-100 C for any system that relies liquid water at atmospheric pressure, and only a little bit beyond that for extremophiles. There is another fundamental limit beyond 100 for high temp when any organic molecule will start to burn or pyrolyze, but the boiling point is already a huge evolutionary hurdle on its own for most places on Earth.
There's a huge amount of life that runs on zero sunlight and instead runs on chemical energy deep in the earth. It makes up maybe 10% to 20% the biomass on earth and a good chunk of its biodiversity and is quite likely where life originated, hundreds of millions of years before photosynthesis evolved. It also quite possibly exists in a similar way on Mars.
An interesting example is D. audaxviator, which runs on uranium and is named after a passage in Jules Verne’s “Journey to the Center of the Earth.”
A lot of it has been discovered fairly recently - there's an unusually interesting nyt article on it all, including how they may transform rocks and continents https://www.nytimes.com/2024/06/24/magazine/earth-geomicrobi... or https://archive.ph/VgzKD
https://en.wikipedia.org/wiki/Last_universal_common_ancestor
Therefore, it's hardly a surprise that "life finds a way" :)
However there are only 2 known ways of obtaining energy for living without photosynthesis, which are called acetogenesis and methanogenesis.
In both cases the inputs are free H2 and carbon dioxide (or alternatively carbon monoxide and water), while the output contains acetic acid for acetogenesis and methane for methanogenesis. Methanogenesis is confined to a certain group of archaea, while the simpler acetogenesis is widespread among bacteria and archaea and there is good evidence that the last common ancestor of all cellular living beings was able to do acetogenesis, using the free hydrogen provided by volcanic gases or hydrothermal vents.
H2S can be used as a source of energy in 2 ways, both of which require photosynthesis. H2S can be used instead of water and oxidized by bacteria that are capable of anoxygenic photosynthesis, or it can be oxidized by using free oxygen that has been produced elsewhere by algae or plants, using solar energy (instead of free oxygen, other oxidizers may be used, for instance nitrate or sulfate, but those must have been produced elsewhere by using free oxygen, so ultimately also by using solar energy; sulfate can also be produced directly using solar energy, in anoxygenic photosynthesis). So H2S cannot be used to obtain energy in the absence of living beings that capture the solar light. (Because the reaction of H2S with CO2 does not produce energy, but it consumes energy.)
Similarly, the living beings that oxidize H2 coming out of hydrothermal vents, using either oxygen or other oxidizers derived from oxygen or from anoxygenic photosynthesis, like nitrate or sulfate, are also completely dependent on the photosynthesis carried on by algae or plants elsewhere.
Only the acetogenic and methanogenic bacteria and archaea are completely independent of solar energy and they depend only on the internal heat of the Earth as a source of energy (which is the ultimate cause of the production of H2 in volcanic gases and in hydrothermal vents, by the reaction of water with magmatic rocks that are chemically stable only at the temperatures from higher depths).
Like other anaerobic bacteria, acetogens, methanogens, and also sulfate-reducing bacteria, are widespread in human guts, where all 3 groups consume the H2 produced by other bacteria in fermentations.
> Beneath that ice, the light sensors recorded an astronomically small number of photons: an upper range of 0.04 micromoles per square meter per second, a number very close to the theoretical minimum amount of light that photosynthesis can run on. The actual amount of light was probably lower.
I was curious how this compared to being on Pluto, but apparently Pluto gets a lot more sunlight than I imagined[1]:
So at high noon on Pluto you’d get at least 60 lux of sunlight.
Civil twilight is roughly enough light to read by, and that’s 3.4 lux. Moonlight is less than 0.3 lux.
60 lux would be comparable to indoor lighting in a hall or stairway.
[1]: https://www.johndcook.com/blog/2018/03/09/could-you-read-on-...
For the Metric Heads, we here in Australia use the SI unit Photons per Olympic Swimming Pool, which unit of measure is the Centiquantalap, naturally.
Edit to add: Under the modern US customary measurement system, 1 drop is 1/72th of a US customary fluid dram, and 793 and 1000 conveniently have no common factors, so it should be self evident that 3 litres is 793/1000th of a US fluid gallon. Converting that to lux or lumens is left as an exercise for the reader.
It is quite amazing to think what evolution has to handle with. The aftereffects after a bad asteroid impact are staggering. No sun for years & the entire earth can get cooked for a few hours from the kinetic energy of the ejecta that gets kicked up. Then everything freezes. So survivors typically do well eating carrion, hibernating and burrowing.
It would be great to run a bunch of experiments at various different conditions and see minimum and maximum on a variety of variables like salinity, acidity, heat, etc
Some types of photosynthesis ALSO optimize for water usage.