Plants reduce the carbon dioxide (CO2) in the atmosphere and create more oxygen, which is needed by all organisms, through photosynthesis. :)
it's very practical, because it's on base 10, so conversion between stuff like meters to kilometer is always just a multiplication with 10 to some power
like 1 km = 1000m (10³m)
or 1 m = 10^-3km = 0.001km
same reason for other SI units.
except time, that's base 60, or 12, or 24. that's more complicated, but there isn't any real competition
I think you just typed the answer in the 2nd paragraph:)
Do you mean "why"?
They are the main source for all living organisms because they provide energy, relatively short term, for any creature that consumes them.
