Geologic Time and Mass Extinctions Chapter 8, Lesson 1 Geologic Time and Mass Extinctions

Time Scale Eons (Phanerozoic & Precambrian) Eras (Paleozoic, Mesozoic, Cenozoic) Periods (ex. Jurassic) Epochs (currently-Holocene)

(as much as a million years) Mass Extinctions Definition: The dying off of many different species of organisms over a short period of geologic time (as much as a million years) Fact: 99 % of all species that have lived on earth are now extinct. Most extinctions occur 1 species at a time Several units on the geologic time scale begin and end with a mass extinction.

Causes of Mass Extinctions Catastrophic Events: An event that causes a drastic change in the number of organisms of one or more species over a short period in geologic time. 3 types of catastrophic events Climate Change 2) Volcanoes 3) Asteroid Impacts Fact: Not all catastrophic events cause mass extinction

sudden changes in climate that can cause mass extinctions Climate Change sudden changes in climate that can cause mass extinctions Global Warming Burning of fossil fuels, such as coal and oil, adds greenhouse gases, like carbon dioxide, to the atmosphere. Many scientists think greenhouse gases in the atmosphere contribute to global warming, a global increase in atmospheric temperature. If the overall temperature of the atmosphere increases, the temperature of the oceans also increases. Because warm water holds less oxygen than cold water, global warming could cause a decrease in oxygen levels in the water. If the oxygen levels drop in shallow waters, where most organisms live, mass extinctions could occur. Global warming could also raise sea levels. Water from melting glaciers would flow into the oceans, causing sea levels to rise. Geologists have found evidence of warm temperatures, a rising sea level, and oxygen-poor waters flooding shallow-water areas. Some scientists think global warming might have been the cause. Global Cooling Mass extinctions could also be caused by global cooling, an overall decrease in atmospheric temperatures. Global cooling could lower sea levels as large amounts of water are frozen in glacial ice. Less water in the oceans would mean fewer warm, shallow-water environments. With fewer warm-water environments, there would be less space to support marine ecosystems. Global cooling appears to have initiated the Ordovician mass extinction event.

Volcanoes Explosive and non-explosive eruptions emitting dust, ash, lava, and gas which affect climate and organisms  The Haze Effect: Suspended particles, such as dust and ash, can block out the earth's sunlight, thus reducing solar radiation and lowering mean global temperatures The eruption of Pinatubo in the Philippines, 12 June 1991, the largest volcanic eruption since 1912. The Toba eruption 73,000 years ago would have looked rather similar, only very much larger: while Pinatubo erupted 4 cu. km of ash, Toba produced at least 800 cu. km.  

Asteroids Jupiter What if a large comet or asteroid hits...... The Shoemaker-Levy Comet Impact with Jupiter gave us a way to test theories of extinction by asteroid impact. Although most dinosaurs were probably killed off in the initial event where debris superheated the upper atmosphere, the after events would have been very destructive too. There would have been huge tidal waves from the shock, and possibly the impact triggered large earthquakes that caused even more. Afterwards, the upper atmosphere would have been saturated with the soot and gases from the massive fires, resulting in years of climate change that included severe acid rain. Jupiter The events on Jupiter agreed closely with the most popular theory for the extinction of the dinosaurs. In this theory, a dramatic impact on the Yucatan coast of a comet or asteroid about 10 km in diameter 65 million years ago killed 16 percent of marine families, 47 percent of marine genera (the classification above species) and 18 percent of land vertebrate families, including the dinosaurs.