mirrored file at http://SaturnianCosmology.Org/ For complete access to all the files of this collection see http://SaturnianCosmology.org/search.php ========================================================== Changing Paleoclimates and Mass Extinctions Mass Extinctions and Model Timing by Donald L. Blanchard *Introduction; Caveats:* Given the incompleteness of the fossil record, it is virtually impossible to assign precise dates to any particular extinction event. Plant and animal communities may disappear at one locale at a different time than the same communities at another site. Disappearances in one location may reflect only changes in local conditions, or changes in the deposition and preservation of fossil material at that location. Furthermore, the last appearance of particular indicator fossils is often used as a reference for correlating the dating between deposits at widely separated localities, and if the disappearances are asynchronous at those locales, a false impression of the suddenness of extinction events can result. Many extinction events seem clearly to have occurred over a duration of several million years, with some indicator fossils disappearing everywhere well before the disappearance of others. In spite of these complications, extinction events can still be dated far more accurately than can paleoclimate indicators. For this reason, published dates for major extinction events have been used as the basis for all cycle periods and obliquity angle computations given in this model. The interval given for a full cycle, composed of one 'WET' climate cycle and one 'DRY' cycle, is derived from the three greatest extinction events known: the End-Cretaceous, at 65 Ma, which wiped out an estimated 20% to 25% of known species; the Late Ordovician (Ashgill), at 448 Ma, at which an estimated 25% to 40% of extant species went extinct; and the biggie, the Guadaloupian / End-Permian, at 256 Ma, during which an estimated 95% to 96% of all species were lost. Both of the latter two events appear to have occurred over a several million year span of time, and the dates used represent the (approximate) onset of the extinction event. These earlier dates represent a better fit with the proposed cyclicity of extinction based on an astronomical mechanism (astronomical cycles *should* be much more precise than paleontological dating). However, arguments exist that the major extinctions within these two events may actually have occurred much later than the dates given, so the model may require some minor adjustments as dates are refined. A fourth extinction event, among a group of calcareous algae known as the acritarchs in the Late Precambrian at approximately 650 Ma, very nearly fits the proposed cyclicity as well. These major extinction events (designated as 'Primary' events) are postulated to have occurred at the transition from a two Hadley Cell circulation pattern (a 'WET' cycle) to a six Hadley Cell pattern (a 'DRY' cycle). As described in the previous chapter , this represents a transition from a uniformly cool and humid temperate climate world-wide to a pattern of hot tropics, frigid poles, and extreme fluctuations in the temperate zone between (i.e. like the climate pattern we have today). Proximate causes of extinction varied with taxons, but all relate to 'WET' cycle organisms being unadapted for the variations in temperature to which 'DRY' cycle organisms are subjected. ------------------------------------------------------------------------ *Causes of Primary Extinction Events:* It is becoming more and more widely accepted that dinosaurs were active, warm-blooded animals, and they unquestionably grew to rather large body size. In warm-blooded animals, the amount of body heat produced is proportional to the cube of linear body dimensions, while heat is shed through the surface, which is proportional to the square of linear dimension (i.e. tripling the length, with proportions remaining the same, yields 9 times the surface area to shed heat, but 27 times the volume to generate it). Thus, large body size serves as an adaption for conserving heat in cold climates, while smaller size, to more efficiently loose excess heat, is favored by hot conditions. This supports the notion that the Age of Dinosaurs -- a 'WET' cycle -- enjoyed a cool temperate climate. It also suggests that dinosaurs didn't require, and so probably lacked, an efficient cooling mechanism for disposing of excess body heat. Given the significantly hotter summers of a 'DRY' cycle climate, the cooling system deficiency of dinosaurs probably caused them to perish from heat prostration. (Dinosaurs first appeared in the Late Triassic, during a 'DRY' climate cycle, but didn't evolve into heroic proportions until the Late Jurassic, after the onset of 'WET' climatic conditions. Dinosaurs of the Late Triassic and Early Jurassic were quite small by comparison.) Birds, dinosaurs' closest relatives, require an extremely efficient cooling system even in frigid climates, to dispose of the excess heat generated by powered flight. Birds' bones are hollow, and the air spaces inside them are connected to their lungs. With every beat of their wings, the powerful flight muscles in their breasts pump air throughout their bodies, providing efficient cooling even during the most energetic exercise. Thus, birds were appropriately pre-adapted to survive the hotter summers of a 'DRY' cycle climate. The other flying vertebrates of the last 'WET' cycle -- the Pterosaurs -- did not have powerful flight muscles, nor the bone structure to support them, and probably flew primarily by gliding on the gentle breezes that prevail during a 'WET' cycle climate. (It is rather difficult to imagine a Pterosaur with a 40' to 50' wingspan, such as the Late Cretaceous /Quetzalcoatlus northropi/, vigorously flapping its wings as most birds do.) One would imagine, however, that they would have had more efficient cooling systems than their dinosaur cousins. But, lacking strong flight muscles, they probably could not have withstood the high winds and atmospheric turbulences that characterize 'DRY' cycle climates, and may well have been simply blown out of the sky -- literally. Very large flying insects, such as the dragonflies with 3' [1 m] wingspans of the Carboniferous period (another 'WET' cycle) likely suffered the same fate. (I believe that flying insects of heroic dimensions also existed during the Cretaceous.) The tree-like giant Club Mosses and Horsetails of the Carboniferous were deficient in woody tissue, and probably wouldn't have fared well in 'DRY' cycle winds either. Many of the plant species that have survived from the last 'WET' cycle, such as cycads, Araucarias (which include the Norfolk and Chilean Pines), redwoods, palms, and most ferns, are found today in places that are not necessarily particularly warm, but where winter temperatures never dip below freezing. Plant survival is generally limited not by average or maximum temperatures, but by the minimum temperature to which the plant is subjected. Given enough water, most plants from the Amazon jungles will survive and even flourish in the arid Mediterranean climate of Southern California gardens (where freezing temperatures are almost unknown), but will die if subjected to one or two hours of below freezing temperatures. Plant communities on land seem to have been largely unaffected by the most recent mass extinctions. The following table shows the correlation between actual extinction events and the predicted climate cycles of the proposed model. ------------------------------------------------------------------------ Predicted vs. Documented Extinction Events [ *KEY:** Primary Extinction Events; * * Secondary Extinction Events. * ] ------------------------------------------------------------------------ * Extinction Event * * Actual Date * * Predicted Date * * Interval * * Climate Cycle * ------------------------------------------------------------------------ 65 MYr DRY End-Cretaceous 65 Ma 65 Ma ------------------------------------------------------------------------ ------------------------------------------------------------------------ 111.5 MYr WET Bajocian 175 Ma 176.5 Ma ------------------------------------------------------------------------ ------------------------------------------------------------------------ 80 MYr DRY End-Permian 248 Ma Guadaloupian 256 Ma 256.5 Ma ------------------------------------------------------------------------ ------------------------------------------------------------------------ 111.5 MYr WET Frasnian/Famennian 367 Ma 368 Ma ------------------------------------------------------------------------ ------------------------------------------------------------------------ 80 MYr DRY End-Ordovician 438 Ma Ashgill 448 Ma 448 Ma ------------------------------------------------------------------------ ------------------------------------------------------------------------ 111.5 MYr WET Mid-Cambrian ??? 559.5 Ma ------------------------------------------------------------------------ ------------------------------------------------------------------------ 80 MYr DRY Late Precambrian 650 Ma 639.5 Ma ------------------------------------------------------------------------ ------------------------------------------------------------------------ ------------------------------------------------------------------------ *Secondary and Tertiary Extinction Events:* The secondary extinction events noted in the table are here associated with the transition from 'DRY' to 'WET' climate cycles. The suggested proximate cause of most extinctions during these events is the loss of the hot, tropical climate zone, which simply ceases to exist during 'WET' cycles. Most of the losses at these events seem to have taken place among reef communities, which are generally confined to tropical waters (Stanley, 1987 ). This also accounts for the lesser severity of secondary extinctions; fewer ecosystems tend to be impacted by the changes. Tertiary extinction events (not shown in the table) are postulated at both of the transitions between six and ten Hadley Cell circulation modes within 'DRY' cycles. These events, of much lesser severity, only show up clearly in the fossil record of the Cenozoic Era, in the Middle Miocene at 11.3 Ma (predicted ~12 Ma) and the Late Eocene at 38 Ma (predicted ~38 Ma). An earlier event at the Norian/Carnian boundary (Late Triassic) at 225 Ma may also be of this form. (The predicted event would be at 229.5 Ma.) The predicted times for all primary, secondary, and tertiary extinction events are indicated in the Geological Time Chart . ------------------------------------------------------------------------ *Extinction-Driven Evolution:* The idea of regular and cyclic extinction events caused by radical changes in climate offers new insights into one of the recurring questions in the Theory of Evolution: that of the apparently sudden explosions of rich varieties of new species. Darwin's original notion of gradual change through natural selection and "survival of the fittest" has fallen away in the face of new paleontological evidence of long periods of species constancy, or 'stassis', followed by very rapid evolution and the abrupt appearance of a great diversity of new species. The current model provides a ready explanation for such sudden episodes of adaptive radiation. Changes in atmospheric circulation are postulated to occur within a relatively brief interval of time, possibly as little as a few hundred to a few thousand years. This is far too short a period for most organisms to evolve and adapt to the new environmental conditions. (There is no cause for immediate concern, however; the next major change is not expected to take place for another 15 million years.) Major changes in the mode of atmospheric circulation invariably cause a total loss of many ecological niches, environmental conditions under which large numbers of species evolved, and to which they had become supremely adapted. Survivors of the change tend to be the least specialized and most adaptable species, or generalists. Confronted with totally new and unfilled environmental niches, these generalists will quickly and opportunistically adapt to the new environment. Evolutionary changes which might have proven unfit to compete for already occupied niches will be able to survive and propagate. Mutations leading to new forms, new body plans, even new organ systems, will have a window of opportunity to survive and develop, provided only that they are biologically viable and that they offer some advantage in the colonization of a new environment. This window of opportunity doesn't remain open for long, for other surviving generalists, or even sibling species of the new opportunists, will quickly move in to compete in the new ecological territory. In as little as a few tens of thousands of years for fast reproducing species such as microorganisms, or up to a few million years for larger species that are slower to reproduce, full competition will be restored and "survival of the fittest" begins to reassert itself. This marks the beginning of an episode of gradual refinement of the new adaptations, and a wringing out of the less successful "hopeful monsters". Those experiments that work best will endure, while others less appropriate to the new conditions will vanish, possibly -- barring a fluke of nature -- without leaving a trace in the fossil record. Extinction-Driven Evolution is thus the notion that periodic extinctions caused by catastrophic changes in climate (at least from the viewpoint of those species that suffer extinction) will periodically "level the playing field" by eliminating species which, although eminently adapted to the old conditions, are unable to survive and compete in the new climatic regimen. Thus new adaptations, new experiments in body plans, new feeding strategies, etc., will be given an opportunity to be tried out, tested in an environment that is essentially free of interspecies competition, and gradually refined until they are suitably adapted to withstand the rigors of a static, "survival of the fittest" environment. Extinction-Driven Evolution thus combines elements of Osborn's ancient notion of "Adaptive Radiation" with that of Gould's proposed "Punctuated Equilibrium." Cyclic changes in paleoclimate provide a logical and self-consistent (if as yet unproven) mechanism to support it. Extinction-driven evolution represents on a global scale the same phenomenon that Darwin observed on a local scale in the Galapagos Islands: the rapid evolution and adaptive radiation that happens when a new species arrives in an isolated and impoverished ecosystem. Climate Change=>Mass Extinction=>Rapid Evolution=>Long Period of Stasis=>Climate Change ------------------------------------------------------------------------ Last updated November 2004. WS Logo Site designed and hosted by: *WebSpinners.com* (info at webspinners.com ) WebMaster: Donald L. Blanchard