What are thermal vents? What did they look like?

Answer 1

A thermal vent is a hole or crack in the earth's surface where naturally heated (hydrothermal) water is escaping. It can be under the sea (black smokers, white smokers) or on land (hot springs, geysers, fumaroles).
Drawing and short write up of deep sea vents:
http://www.divediscover.whoi.edu/vents/vent-infomod.html

If you want photos of terrestrial or submarine vents, do a google image search for "thermal vents" -you'll get lots.
Wikipedia has a pretty good write up: http://en.wikipedia.org/wiki/Hydrothermal_vent

Answer 2

do they on land have a dark grayish sluggy dirt which will sink materials laying or tossed upon it.