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This is a terrific book that provides a comprehensive view of the earths environmental history and the rise and fall of various groups of life. Most importantly it provides a view of extinction that is far more insightful than is generally depicted.Leigh Van Valen created survivor curves for 24,000 fossil taxa, showing that on average a bivalve species lasts 5 million years while a mammal species lasts only one million years. Currently living species represent only 1% of all species that have lived. It is estimated that less than 5% of all fossils species are known to man.Stage level extinction looks at the percent of species lost in each stage (subdivision of epoch / period). While the big five extinctions are evident, significant extinction occurred in other periods: some greater than the big five. Some 95 % of all extinctions have happened at other than the big five events, and are categorized as background extinctions.Proximate extinction mechanisms are the conditions that cause extinctions such as global cooling or sea level change, while ultimate extinction mechanisms are those that induce the change such as volcanoes or asteroid hits.Proximate Extinction mechanisms:- Global cooling is increased by variation in solar radiation, atmospheric composition (reduction in greenhouse gases) and cloud cover. An increase in cloud cover increases the earths albedo reflecting more radiation back into space. Low sea levels are cooling as the oceans absorb radiation.- Sea-level change occurs as the amount of glaciation changes, but also as a result of plate tectonics where swelling of the mid-ocean ridges reduces the volume of the ocean basins. Sea-level change affects islands as the number of species supported by an island varies with the log of the area. Continentality occurs when lower sea levels expose more land which heats more readily, increasing the dryness of the isolated interiors.- Marine anoxia when the pycocline, separating the upper well oxygenated waters from the lower less oxygenated waters, is strengthened by temperature or salinity differences. Anoxia tends to increase with global warming and is signalled in the rocks by organic rich, dark shales. Rising sea levels can expose continental shelves to low oxygen waters, leading to the extinction of species adapted to greater oxygen levels. - Ocean and atmosphere circulations are nicely described and diagrammed in this book. Atmospheric circulation strongly influences heat and precipitation patterns, and can be changed by mountain uplift, extensive icefields and large volcanic eruptions. Ocean circulation is governed by the shape of the ocean basins - it is believed there was no deep water circulation before 10 - 15 mya. These circulations affect the distribution of anoxic bottom water.Ultimate Extinction mechanisms include variation in solar radiation, plate tectonics, Large Igneous Province (LIP) volcanism and large bolide (meteor, comet and asteroid) impacts.The Pre-cambrian Extinction - The Ediacaran organisms were soft bodied with a distinctive tube-like form. No record has been found of their survival into the Cambrian. Little is known of the conditions nor of the extinction event.Cambrian Biomere Extinctions - Investigation of Canadian trilobite fossils has revealed at least seven major extinction events during the Cambrian. Victims were brachiopods, conodonts and trilobites. Sea level change and anoxia are best supported as the mechanisms for these extinctions.End-Ordovician Extinctions - During the Ordovician, the trilobites, brachiopods, rugose corals, tabulate corals, crinoids and nautiloid cephalopods flourished. Major losses of species occurred for all of these groups in the late Ordovician extinction event. The Ordivician was a period of warm climate, but low oxygen levels. It is generally thought that the proximate cause was sudden glaciation and possible changes to deep oceanic water circulation bringing anoxic water into the shallows. The glaciation lasted a short 500,000 years before returning to a warm climate creating a strong oceanic thermocline again driving anoxic water into the continental shelves.Late Devonian Extinctions - Following the Ordovician, the Silurian radiation featured brachiopods with articulating shells, ammonoid cephalopods, advanced echinoderms, fish, early land plants and the first insects. Late Devonian extinctions took out 20% of the marine families, 60% of the marine genera and 80 to 90% of the marine species. The land plants suffered few extinctions. Proximate causes appear to be sea level rise, global cooling and anoxia. Ultimate causes include inconclusive suggestions of bolide impact and the Vilnuy Volcanic Province. However, the late extinction appears to have been a result of extensive glaciation due to a re-occupation of the southern pole by Gondwana.Late Permian Extinctions - Man of the Devonian reef builders survived, but lost the habit of forming large reefs typical of the Devonian. Large advanced reptiles evolved. While high in the early Carboniferous, sea levels fluctuated in the late Carboniferous, periodically submerging the extensive swamps and leading to the coal deposits. Over 90% of all species perished in the Late Permian Extinctions - fewer among the land plants, but greater among the lesser marine animals. The Late Permian extinctions span an interval of about 5 million years. The sea level rose at at moderate pace through the late Permian and are not considered a proximate cause. Evidence exists of high temperatures due to continentality, and of marine anoxia. As to ultimate causes, evidence of large bolide impact is minimal. The prime suspect are the Siberian Traps which extruded 2 to 3 million cubic km of basaltic lava.Late Triassic Extinctions - In the Triassic, more modern groups began to dominate including, diatoms, sponges, marine arthropods, bony fish, lizards, pterosaurs, archosaurs, and ferns. While the sea level rose gradually through the Triassic due to continental movement, it dropped sharply toward the end although there is uncertainty as to the magnitude and the timing. Black shales indicate the spread of oxygen poor oceanic water over the continental shelves. While the Guarda crater in Portugal is dated to the late Triassic, there is little other evidence of it having a role in this extinction. Extensive volcanism occurred in the Central Atlantic Magmatic Province (CAMP) at the end of the Triassic and put further stress on the biosphere. The min group that was completely lost were the conodonts.End-Cretaceous Extinctions - While many of the groups present in the Triassic continued into the Cretaceous, many new animals appeared including the rudists, large bivalves that formed reefs, mosaurs, plesiosaurs, the large dinosaurs, birds and pterosaurs. The continents started to separate during the Jurassic. Aided by the ocean currents, the climate organized into tropical, temperature and cooler zones (although the polar climate was still quite warm). Sea level rose through the Mesozoic, with a large drop (100 to 150 m) at the end of the Cretaceous. While the Cretaceous extinction was the smallest of the big five, losses included the ammonites, brachiopods, the rustid bivalves, pterosaurs, mosaurs, plesiosaurs and the non-avian dinosaurs. Extinctions occurred continuously through the Mesozoic, but were greatest at the end of the Jurassic and Cretaceous. The Western Interior Seaway formed in the early Cretaceous due to subduction and disappeared at the end of the Cretaceous when the sea level fell. The Deccan Traps cover some 500,000 sq km. It appears that 80% of the activity occurred over as little as 50,000 years at the end of the Cretaceous. Proximate extinction mechanisms are generally considered to be cooling and ozone depletion due to the volcanism. There is a difference of opinion in the scientific community as to whether the Chicxulub impact was a cause of the Cretaceous extinction. Many, including the author, feel the evidence is that the impact effects would have been great but too localized to account for the extensive extinctions.Palaeogene Extinctions - During the Palaeogene the continent continued to drift towards their present positions. The opening of the Drake Passage between South America and Antarctica allowed modern southern ocean currents to become established. While cooler tan the Cretaceous, climates were warmer than today. At the end of the Palaeocene, the Palaeocene-Eocene Thermal Maximum (PETM) occurred. Temperatures fell in the late Eocene, as did the sea level (100 m). Both extremes produced extinctions. The south polar ice-cap formed in the late Eocene. Extinctions included a number of mammal groups and the champosaurs. The separation of Antarctica and the establishment of deep water currents resulted in long term cooling. Volcanism in the The Ethiopian-Yemen Volcanic Province (2 million sq km) was a second factor. While a number of bolide craters have been identified from this time, but do not tie well with the extinction record.Neogene and Quaternary Extinctions - The Miocene saw the expansion of the Antarctic ice-cap, the disappearance of the Tethys Sea and volcanic activity in the Columbia River Volcanic Province. The spread of grasslands caused specialized grass foragers to dominate. In the Pliocene, the mix of animals changed on all continents due to diversification and migration. The Isthmus of Panama emerged about 3.5 mya. The first permanent northern ice-cap formed 3 mya. The Pleistocene was characterized by very cold temperatures and extensive glaciation, with warmer periods termed the interglacials. The Milankovitch Cycles produce a 100,000 year periodic variation in climate that are evident over the past 400,000 years. The Cycles are the subject of much current research which is revealing earlier evidence. While overall extinctions were low, megafaunal extinctions were 70% in North America, 80% in South America, 81% in Australia, but few in Europe and Asia. The climate change hypothesis sees the cause as physical and biotic changes to the environment. The overkill hypothesis sees the cause as human hunting and habitat changes, although this explanation is not applicable outside North America.Modern Extinctions - While it appears that modern extinctions are greater than historical, largely due to human disruption of the environment, they fall short of the great extinctions where entire categories of habitat were destroyed.In conclusion, extinction intensities are seen to be a continuous distribution. The big five extinctions represent intervals where the same processes occur coincidentally. The Single Cause (SC) concept of extinction has given way to the Multiple Interacting Causes (MIC) concept. Sea level change and Large Igneous Province (LIP) volcanic events correlate well with extinction intensities, while bolide impacts do not.

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