Una Smith una at
Mon Oct 17 20:19:47 EST 1994

NEC95ISA09 at writes:

>... primative plants, i.e., Liverworts, Hornworts, and moss are
>considered to be ancestors to blue green algae.

It's the other way around:  the algae came first.  In any case,
modern liverworts, hornworts, and mosses are not "primitive";
they've been around longer, and are therefore just as evolved
as other plants.  They are less complex, morphologically, but
simplification is an important part of evolution in many groups.

>... they are nonvascular plants which mean they live in moist,
>shady areas.

"Nonvascular" means lacking a particular tissue adapted for
water transport.  Not all nonvascular plants live in moist or
shady places:  some live in extremely dry, hot environments.

>... gametophytes are produced which produce sporophytes. ...

The vascular plants also show this alternation of generations.

For the rest, a botany or paleobotany textbook will give many
details about what we believe the early atmosphere was like.
The story is a bit too elaborate to reproduce here in a brief
fashion (and anyway I'd be extracting it from a textbook).

	Una Smith		una.smith at

Dept. of Biology, Yale Univ., New Haven, CT  06520-8104

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