Is There a Limit to How Small Life Can Get?

Bacteria can get pretty small, with sizes ranging typically from .2 to 10 microns.
But can organisms get even smaller?
Answering that question isn’t just a fun trivia fact, but could help us in our search
for extraterrestrial life.
Viruses can get even smaller than bacteria, with a single virus getting as small as just
20 nanometers, or ten times smaller than even the most itty bitty bacterium.
Technically though we don’t really count viruses as being alive.
They don’t eat or have a metabolism, but even if they did they still can’t replicate
on their own.
They need to hijack a host like a bacterium in order to make copies of themselves, so
without a host a virus can’t multiply.
To really be alive an organism has to fit all the microscopic machinery that allows
it to eat and self-replicate inside itself.
And since these machines are on a molecular scale, they’re limited by fundamental laws
of the universe.
They can only get as small as molecules and atoms will let them.
So with that in mind scientists have calculated that the absolute minimum size a free-living
organism can be is theoretically around 200 nanometers in diameter.
So far that prediction seems to be holding up, as the smallest living microbes we’ve
found are about that size..
And this lower size limit doesn’t just apply to Earth microbes, it’s universal for all
carbon based life.
But for some, they’re hoping that limit is off.
In 1996 researchers proposed nanoscopic structures in a Martian meteorite might be the remains
of tiny life forms they dubbed nanobacteria.
These supposed nanobacteria fossils were a tenth the size of what we think is possible,
too small to fit a single ribosome, a structure cells need to make proteins so the claim was
met with a lot of skepticism and was never proven.
So sorry to dash your hopes about aliens but it looks like 200 nanometers is about as small
as life can get.
But that doesn’t mean we should stop looking.
Here help me look.
Even microorganisms have a story to tell.
But they can’t make a website.
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Worried about super bacteria?
Check out this video on how scientists are using their own defenses against them.
The smallest microbe we’ve found looks packed to the brim with DNA and scientists think
it has to be parasitic to survive, so I wouldn’t get your hopes up that independent life will
be smaller.
That’s all for now, thanks for watching Seeker!
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Is There a Limit to How Small Life Can Get?

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