It is with carbonate rocks that we see most distinctly that life is a geological process (trademarked, all rights reserved). The large majority of carbonate sediments are directly derived from living systems, and as such they are excellent indicators of past depositional environments. You will want to see these ultimate mineralogy pages for calcite, aragonite and dolomite. For simple introductions to carbonate sedimentology, visit the excellent carbonate pages from the Texas Bureau of Economic Geology. (They have nice online review questions!) As we approach more detailed carbonate topics, please visit the Wikipedia page on carbonate biomineralization, and this one on carbonate classification. There are some good photomicrographs of carbonate rocks (and others) on this Oxford University webpage. And we must take a field trip to the Bahamas someday, but for now we have to do it virtually!
Geology in the News –
A newly discovered sauropod dinosaur in Argentina has extended neural spines, headlined as having a “bony Mohawk”. These spines were not weapons and may have had sexual selection value.
Melting glaciers in Greenland (bad news) are forming new deposits of sand (good news). I had no idea plain old quartz sand had such economic value. There are even sand-based mafia!
A gorgeous multi-layered, multi-spectral view of the Whirlpool Galaxy, courtesy of the venerable Hubble Space Telescope.