CH09: Extinctions

FIGURE 9.1 Timeline of extinction events. Major extinctions are indicated by yellow bars. Global coral reef gaps accompany each of the 5 major past extinction events. Along with climate change, impacts and volcanic episodes are leading possible causes of major extinction spasms. Source: Reproduced with permission from Christopher R. Scotese.

FIGURE 9. 2 Major and minor extinctions FIGURE 9.2 Major and minor extinctions. Diversity of genera over 500 million years. (a) The red plot shows the numbers of known marine animal genera versus time. (b) The black plot shows the same data, with single-occurrence and poorly dated genera removed. The trend line (green) is a third-order polynomial fitted to the data. (c) Same as (b), with the trend subtracted and a 62-million year (Myr) sine wave superimposed. (d) The detrended data after subtraction of the 62-Myr cycle and with a 140-Myr sine wave superimposed. Dashed vertical lines indicate the times of the five major extinctions. Source: Rohde and Muller (2005).

FIGURE 9.3 Marine benthic habitats before and after the Permian–Triassic extinctionevent. A marine fauna of 100 or more species is reduced to less than six species based on seabed reconstructions off south China. Source: Benton and Twitchett (2003).

FIGURE 9.4 End-Eocene global cooling. The initiation of the first permanent Antarctic ice sheets in the past 100 million years coincided with end- Eocene cooling, indicated by an arrow at approximately 34 mya. Source: Zachos et al 2001. Reproduced with permission from Yale University Press.

FIGURE 9.5 Methane outgassing. Methane trapped in sediments as clathrate may be released during periods of warming - inter-glacial periods (interstadials, a), because warm methane hydrates are unstable (b). But in cool, glacial periods (stadials, c), hydrates are stable and no methane is released into the atmosphere (d). Outgassing from sediments in the Santa Barbara channel during interglacial periods is illustrated in this drawing. Release of methane from clathrates has also been implicated in the rapid warming at the Paleocene–Eocene thermal maximum. Source: Reproduced with permission from AAAS.

FIGURE 9.6 Species lost at end-Pleistocene. Some of the dozens of species lost in North and South America at the end of the Pleistocene are illustrated, including saber-tooth cats (Smilodon) and wooly mammoth (Mammuthus primigenius). Source: From Wikimedia Commons.

FIGURE 9.7 Declining mammoth range. Modeled loss of mammoth range due to human expansion (dark line) and climate change (color ramp; red most suitable), from 126,000 years ago (126 kyr BP) to the end of the Pleistocene. Source: Nogues- Bravo et al. (2008).