Comments on: Arizona Geological History: Chapter 2, Cambrian and Ordovician Time

By: Warren Lewis

Warren Lewis — Sun, 22 Nov 2009 01:56:19 +0000

Any comment on Saltzman et al, http://researchnews.osu.edu/archive/earlyice.htm? They say CO2 levels dropped immediately before the Ordovician ice age started owing to the weathering of the new Appalachian mountain chain. Seems to be supported by Beerling et al, http://adsabs.harvard.edu/abs/2008AGUFMPP41D1486B

By: Jonathan DuHamel

Jonathan DuHamel — Fri, 11 Sep 2009 01:31:43 +0000

Question 1: The evolution of the carbon cycle and of atmospheric CO2 over Phanerozoic time is based on a variety of geological, geochemical, biological, and climatological data.

“On a multimillion year time scale the major process affecting atmospheric CO2 is exchange between the atmosphere and carbon stored in rocks. This long-term, or geochemical carbon cycle is distinguished from the more familiar short-term cycle that involves the transfer of carbon between the oceans, atmosphere, biosphere, and soils. In the long-term cycle loss of CO2 from the atmosphere is accomplished by photosynthesis and burial of organic matter in sediments and by the reaction of atmospheric CO2 with Ca and Mg silicates during continental weathering to form, ultimately, Ca and Mg carbonates on the ocean floor (after transport of the weathering-derived Ca, Mg, and carbon to the sea by rivers). Release of CO2 to the atmosphere in the long-term carbon cycle takes place via the oxidative weathering of old organic matter and by the thermal breakdown of buried carbonates and organic matter (via diagenesis, metamorphism and volcanism) resulting in degassing to the earth surface.”
Read: Berner, R.A. and Kothavala, Z., 2001, GEOCARB III: A revised model of atmospheric CO2 over Phanerozoic time: Am. J. Sci., v. 301, p. 182-204,

or: Rothman, D.H. 2002. Atmospheric carbon dioxide levels for the last 500 million years. Proceedings of the National Academy of Sciences USA 99: 4167-4171.

to see how they derive CO2 concentration from weathering rates.

The geologic reconstruction of temperature is based on oxygen-18 isotopes from fossils and cave stalagmites.

Question 2: Carbon dioxide has nothing to do with ice ages, see: Veizer, Jan, 2005, Celestial Climate Driver: A Perspective from Four Billion Years of the Carbon Cycle, Geoscience Canada, V. 32, no. 1

Question 3: Yes, real science contradicts the phantom menace.

By: Geognostic

Geognostic — Thu, 10 Sep 2009 19:24:32 +0000

Yes, very interesting. This is starting to feel like the beginning of a James Michner book.

Just a couple of questions. How do you know just how much atmospheric carbon dioxide was present in the Cambrian and Ordovician? And, if that much was indeed present how could there be an Ice Age? That scenario would seem to contradict everything that we are hearing about global warming today.

By: leftfield

leftfield — Wed, 09 Sep 2009 19:47:00 +0000

Two thumbs up! Very interesting.

By: Helen

Helen — Wed, 09 Sep 2009 18:09:48 +0000

This is fascinating. Thank you

By: Jonathan DuHamel

Jonathan DuHamel — Wed, 09 Sep 2009 17:49:32 +0000

Many of the names came from the early British geologists. For instance, the name "Cambrian" refers to Cambria, the ancient name for Wales. The Ordovician was named after the Ordovices, an ancient British tribe in N Wales, where rocks characterizing the period were found.

By: ldonyo

ldonyo — Wed, 09 Sep 2009 16:57:26 +0000

As always, very interesting stuff, Jonathan!

I’ve always wondered just where the names for epochs came from and who decided them? Was there a lot of drinking involved in the process?