|MadSci Network: Earth Sciences|
Hi Benjamin, This is a very good question, and it may take a while to answer. Tornadoes are produced by severe thunderstorms that occur when air masses with different properties come into contact. (1) Since we should expect that weather has been around as long as Earth's atmosphere there probably were tornadoes in the time of dinosaurs. I don't know how common they were, though. Dinosaurs were around during the Mesozoic Era, 275-65 million years ago. According to studies of plant fossils from that time, and also chemistry of sediments of that age, the climate was tropical over much of the planet. (2) It seems to me that since the climate seems to have been pretty constant over most of the planet at the time, that *could* mean fewer tornadoes, since contrasting airmasses would be more similar. Also tornadoes seem to be less common in tropical climates, except perhaps in association with hurricanes. But this is only my guess. It is hard enough to anticipate what our climate will do over the next 50 to 100 years. However, there were probably less tornados in most places than what you see in Illinois today, because the US and Canada record the highest number of tornado incidence in the world (1), though in some places many more tornadoes may be happening but not being recorded. Nonetheless because tornadoes are so common in the US and particularly the Midwest, I think it is safe to say that however many may have occured in an average place in the time of dinosaurs was lower than much of the modern-day US. And really, there isn't anything that we can do to be sure how often tornadoes happened. Storm deposits in general are commonly found in rocks that were deposited in shallow ocean water. But tornadoes, for all the problems that they cause, don't move much sediment at all and are very small. That means that little evidence of a tornado is likely to be found in the rock record. Having said that, I am aware of a single instance of an event preserved in a rock outcrop that *may* have been a tornado. Carozzi and Gerber (1978) (3) reported a region of broken-up sediment (now rock) in a Missouri limestone. The deposit was about 1 foot thick and about 100 feet across. The authors said: "However, the touch-down of a tornado-like system behaving like a funnel is suggested rather than the passage of a storm front sweeping a shallow carbonate platform" (p. 706) The rock unit (Burlington Limestone) affected by this possible tornado is Mississippian in age which makes it a lot older than the dinosaurs (325- 360 million years). Here is a webpage that talks about the Burlington Limestones: http://www.lakeneosho.org/Miss26.html Good luck fossil-hunting. If you don't know about it already, this map might help you identify what you find: http://www.isgs.uiuc.edu/nsdihome/browse/statewide/bedgeob.gif It will tell you about how old the rocks are where you are looking. It's from the Illinois State Geological Survey. http://www.isgs.uiuc.edu/isgshome/bed-geo.htm Have fun out there! --Gene Marlin (1) "How is a tornado formed?" on the MadSci website: http://www.madsci.org/posts/archives/may96/826319592.Es.r.html (2) http://www.palaeos.com/Mesozoic/Mesozoic.htm (3) Carozzi and Gerber, 1978. Synsedimentary Chert Breccia: A Mississippian Tempestite. SEPM Journal of Sedimentary Petrology. September 1978, Vol. 48, Number 3 pp. 705-708.
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