[HN Gopher] Longer days on early Earth may have set stage for co...
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       Longer days on early Earth may have set stage for complex life
        
       Author : jdmark
       Score  : 43 points
       Date   : 2021-08-04 14:08 UTC (8 hours ago)
        
 (HTM) web link (www.sciencemag.org)
 (TXT) w3m dump (www.sciencemag.org)
        
       | lend000 wrote:
       | Maybe I'm missing something obvious, but shorter days mean
       | shorter nights. The whole premise (that longer days gave
       | cyanobacteria more time to accumulate oxygen that they would
       | consume at night), at least as interpreted by this pop-sci
       | article, makes no sense to me. There may be other more complex
       | reasons for the change in rotational speed less directly
       | affecting oxygen in the atmosphere, but it's only a sample size
       | of two (and they ignore the third one where atmospheric oxygen
       | has decreased since the time of the dinosaurs), so there isn't
       | much to go on.
        
         | dredmorbius wrote:
         | Photosynthetic activity occurs at a relatively low efficiency.
         | If the net energy demands during day and night cycles is not
         | constant, then adding more time to the day _could_ result in a
         | surplus oxygen production, as the article suggests.
         | 
         | Mind, I've generally found the Great Rusting narrative to be
         | fairly convincing: all the highly oxidised rocks on Earth's
         | crust quite likely didn't arrive on the planet in that form,
         | and picked up free oxygen as it was introduced to the
         | atmosphere, effectively buffering the new addition. Though
         | perhaps a slowing rotation did help reach and flip the tipping
         | point of the Great Oxygenation Event.
         | 
         | Reliable witnesses from the period are hard to find.
        
         | DylanBohlender wrote:
         | I think the premise here is that there is some sort of physical
         | limitation that causes cyanobacteria to have a maximum
         | "carrying capacity" of oxygen, and stretching timecycles causes
         | that threshold to be exceeded, leading to oxygen leaks.
         | 
         | Analogously, think of memory management in a computing context.
         | You have a program running that gradually allocates memory
         | linearly over a certain time period (daytime), but then
         | releases all that memory linearly during another time period
         | (nighttime). Say you're dealing with 4GB of memory and you run
         | the memory-increasing part for 6 hours, then run the memory-
         | decreasing part for the next 6 hours, and so on. Suppose you
         | never allocate the full available 4GB when you're dealing with
         | a 6 hour on/off timecycle (the rate of memory allocation is too
         | low to get to 4GB in 6 hours) - but what happens if you extend
         | the timecycle? There's some timecycle length at which you will
         | finally attempt to allocate more memory than the 4GB your
         | hardware is capable of, so the host OS starts swapping or
         | writing stuff to disk to deal with the excess.
         | 
         | Biological systems don't have a "host OS" that regulates their
         | molecular byproduct management though. Extra atoms/molecules
         | are just going to escape into the surrounding environment.
         | Perhaps the oxygen buildup during the daytime might have worked
         | this way with the cyanobacteria - longer days led to more
         | oxygen being produced than could be physically retained in the
         | immediate vicinity of the cyanobacteria (some type of
         | saturation effect), so all the oxygen in excess of the
         | saturation threshold effectively "escaped" and became
         | unavailable for metabolic "re-consumption" at nighttime.
         | Thinking about the longer nights that accompany the longer
         | days, there's probably a period of time in these longer nights
         | during which all the "nearby" oxygen has been fully consumed,
         | and the cyanobacteria more or less sit idle.
         | 
         | Oxygen saturation in the surrounding environment seems like the
         | missing logical piece from this popsci article.
        
         | lordnacho wrote:
         | I think the idea is that if the night comes soon after the
         | oxygen is produced, it can be reabsorbed quickly. If the day is
         | longer the oxygen has more time to diffuse out of where it was
         | produced, such that it's gone by the time the night comes.
        
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       (page generated 2021-08-04 23:01 UTC)