Re: First life form on earth

in article [EMAIL PROTECTED], Red Dragon at
[EMAIL PROTECTED] wrote on 11/21/03 2:15 PM:

> My view of plant is a living organism that can manufacture  its own food
> from sun energy whereas an animal has need to seek out food.  Therefore
> under this definition,  the bacterium-like beast is an animal.
> I was relying on logic that the first living organism on Earth,  perhaps the
> size of a virus,  has got  to be a plant  If it was an animal, then it can
> only exist by cannibalism, eating its own kind,  which is  rather illogical.
> 
> [moderator's note: You are leaving out some other important routes
> for making a living -- in particular, chemautotrophy, or extracting
> energy from chemical sources, rather than solar inputs. Having just
> seen a neato-keen IMAX film on deep-sea vents, chemautotrophy immediately
> occurred to me to be a potential early survival strategy. - JAH]

Yup.  They ate energy-rich macromolecules just like those that underpin food
webs at hydrothermal vents.  Those communities also have no access to the
products of photosynthesis.

> I was thinking that if the first life on Earth was a plant and somewhere
> down the line there existed an animal life form,  then there has got to be
> an interface of an organism in the transition stage,  half plant and half
> animal.  That was what I meant  about how plant become an animal.

OK.  I was confused because your premise seems clearly false to me.  I think
the data very strongly reject the notion that animals evolved from plants.

> However there could have been an organism that was neither plant nor animal
> which has perhaps gone extinct today.  But I cannot picture the form of this
> creature and I dont know how it acquire its food.

There are plenty of creatures on earth today that are neither plant nor
animal, although I am using a more formal and narrow definition of animal
than the one you described above.  In fact, if you define plants as anything
that can make its own food, and animals as anything that cannot, then there
doesn't seem to be any middle ground into which an organism could fit.

Guy