Paleoclimate and Plate Motions

Rocks that can tell us something about the climate in which they formed are called “lithologic indicators of climate”. Some of the more common climate indicators are coals (green dots), which occur where it is wet enough for vast rainforests to grow; salt (yellow dots) which precipitates from seawater in hot and dry climates where the rate of evaporation is very high; and tillites (black dots) which are a special kind of conglomerate that’s deposited near melting glaciers. The other lithologic indicators of climate that appear in this animation are: bauxites (blue dots - hot & wet), desert soils (orange dots - dry), and warm temperate soils (light blue dots- warm & sometimes wet). The idea is basically very simple. By plotting the geographic occurence of different lithologic indicators of climate, we can map out the extent of ancient climatic belts. We see a tropical wet belt near the Equator (green and blue dots), a desert belt (yellow and orange dots), a high latitude temperate wet belt (green and sometimes black dots), and a polar ice cap (black dots). The Earth’s climate has shifted from “Ice House“ conditions - like today’s climate, to “Hot House“ conditions - like the time of the dinosaurs. When you see black dots that means there is ice at the pole(s) and the Earth is experiencing “Ice House“ conditions. When there are no black dots near the pole, the Earth is in a “Hot House“ climate. My co-authors and I have published an Atlas of Phanerozoic Paleoclimate15 made up of 28 paleoclimatic reconstructions (Boucot et al., 2013). This is where the data for the animation comes from. Over 8000 lithologic indicators of climate are plotted on these maps. These maps record the on-the-ground, factual evidence that describes the state of the Earth’s climate during the past 540 million years. During that time there have been four hothouse and four icehouse worlds. We are now living in an Ice House world. The big question is whether the current episode of global warming will melt the polar icecaps and pouch the Earth’s climate into a Hot House World. Boucot, A.J., Chen Xu, and Scotese, C.R, 2013. Phanerozoic Paleoclimate: An Atlas of Lithologic Indicators of Climate, SEPM Concepts in Sedimentology and Paleontology, (Print-on-Demand Version), No. 11, 478 pp., ISBN 978-1-56576-289-3, October 2013, Society for Sedimentary Geology, Tulsa, OK.