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I am not sure by what criteria you can say these are billion year old living organisms. If you meant they have been around that long, sure, they have, but a st

by cheph 6y ago

I am not sure by what criteria you can say these are billion year old living organisms. If you meant they have been around that long, sure, they have, but a stromatolite is not a living organism by most (if not all?) definitions. It is a layered sedimentary formation. It is about as much an organism as an ant heap without ants is an organism. And I'm pretty sure that none of the individual organisms that create stromatolites are even close to a 100 years old, never mind a billion years old.

taneq 6y ago
I've always wondered the same. They're only an organism in the same sense that a reef is an organism.
mytailorisrich 6y ago
They are not claiming that those very organisms have been alive for that long (the title is poorly worded). The point they are making is that stromatolites have existed for billions of years according to the fossil records.
- cheph 6y ago
  My complaint is exclusively with the title, not the article, which I don't think supports the claim in the title.
rflrob 6y ago
How “old” is a single-celled organism? I don’t know the precise details for Cyanobacteria, but it could be a relatively equal split (unlike budding, a perfectly reasonable alternative). In that case, are both offspring of a cell division the age of the “parent”? If so, why stop at the time since one generation? “But wait”, you may complain, “they are constantly exchanging molecules with their environment!” So is the “age” of the organism the point at which none (or equivalently half or any other fraction you choose) of the atoms inside the organism were inside the organism previously? That implies you could watch a single, discrete cell not dividing, and it’s “age” would be constantly fluctuating, not simply monotonically increasing. It’s entirely possible that age is not a meaningful, well-defined concept here. But less philosophically, when people refer to “living fossils”, they generally mean that the organisms haven’t changed much in form or physiology in a long time. There’s no reason to believe that they aren’t subject to the same pressure to adapt to changing conditions via natural selection, but those adaptations aren’t readily visible.
- cheph 6y ago
  > How “old” is a single-celled organism? Good question, I looked around a bit for this, it seems the life of a single celled organism is taken to be from division to the next division, but really this is a bit odd, because nothing died there. Clearly age for such organisms is not a well defined concept.
  - deleted 6y ago
    [deleted]

by cheph 6y ago

taneq 6y ago

I've always wondered the same. They're only an organism in the same sense that a reef is an organism.

mytailorisrich 6y ago

They are not claiming that those very organisms have been alive for that long (the title is poorly worded). The point they are making is that stromatolites have existed for billions of years according to the fossil records.

cheph 6y ago
My complaint is exclusively with the title, not the article, which I don't think supports the claim in the title.

rflrob 6y ago

How “old” is a single-celled organism? I don’t know the precise details for Cyanobacteria, but it could be a relatively equal split (unlike budding, a perfectly reasonable alternative). In that case, are both offspring of a cell division the age of the “parent”? If so, why stop at the time since one generation? “But wait”, you may complain, “they are constantly exchanging molecules with their environment!” So is the “age” of the organism the point at which none (or equivalently half or any other fraction you choose) of the atoms inside the organism were inside the organism previously? That implies you could watch a single, discrete cell not dividing, and it’s “age” would be constantly fluctuating, not simply monotonically increasing. It’s entirely possible that age is not a meaningful, well-defined concept here. But less philosophically, when people refer to “living fossils”, they generally mean that the organisms haven’t changed much in form or physiology in a long time. There’s no reason to believe that they aren’t subject to the same pressure to adapt to changing conditions via natural selection, but those adaptations aren’t readily visible.

cheph 6y ago
> How “old” is a single-celled organism? Good question, I looked around a bit for this, it seems the life of a single celled organism is taken to be from division to the next division, but really this is a bit odd, because nothing died there. Clearly age for such organisms is not a well defined concept.
- deleted 6y ago
  [deleted]