1. HARBINGERS OF THE LATE PALEOZOIC ICE AGE
1. The percentage of carbon dioxide in the atmosphere is now 0.04 and steadily rising because of the burning of fossil hydrocarbons—many of Carboniferous age.
2. Anaerobic photosynthesizing bacteria: purple sulfur, purple nonsulfur, green sulfur, green nonsulfur, and heliobacteria. Aerobic photosynthesizing bacteria: cyanobacteria.
3. CO2 + H2O → CH2O + O2↑.
4. CH4 + 2O2 → CO2 + 2H2O.
5. Five to 18 percent of the atmosphere’s present 21 percent level of oxygen (Lane 2002).
7. Given its short duration, some question whether the Gaskiers was a snowball-Earth glaciation at all—it may instead have been the first of the Phanerozoic-style glaciations (Pu et al. 2016).
9. The discovery of soft-tissue fossils of the enigmatic hyoliths has now demonstrated that the hyoliths were lophophorates (Moysiuk et al. 2017).
10. In the Oligocene Epoch.
11. Aerobic: CO2 + H2O → CH2O + O2; anaerobic: CO2 + 2H2S → CH2O + H2O + 2S.
12. CO2 + CaSiO3 → CaCO3 + SiO2.
13. CH4 + 2O2 → CO2 + 2H2O.
14. A mineral formed at very high pressures and temperatures deep in the Earth.
15. Measuring the total duration of the Late Paleozoic Ice Age from an onset in the late Frasnian Age of the Late Devonian, 375 million years ago, to an ending in the Wuchiapingian Age of the Late Permian, about 260 million years ago.
16. Another significant accumulation of coal-rich strata also occurred in the Paleogene (Nelsen et al. 2016).
17. Zachos et al. (2001) estimate the size of the Oi-1 ice sheet to have been 50 percent of the present-day ice sheet, or 7.0 × 106 km2, which is here taken as a minimum estimate. Pusz et al. (2011) give an average estimate of the Oi-1 ice sheet that is 85 percent of the present-day ice sheet, or 11.9 × 106 km2, which is here taken as a maximum estimate.
18. By 12 million years ago in the Miocene, sea level had fallen to the level present in our modern-day state of glaciation (Westerhold et al. 2005); thus the initial estimate of the size of the Miocene ice sheet in Antarctica is 14 × 106 km2, the same as today, and this value is here taken as a minimum estimate. However, Wilson and Luyendyk (2009) have argued that the Transantarctic Mountains in Antarctica are a small remnant of a previous highland and that West Antarctica once was exposed above sea level, increasing the total land area of Antarctica by 10 to 20 percent in the earlier Cenozoic. The Miocene ice sheet may thus have been as large as 15.4 to 16.8 × 106 km2, and the upper value is here taken as a maximum estimate.
21. The Famennian Gap spanned ten conodont zones and was estimated to have been seven million years in duration based on the Gradstein et al. (2004) geologic timescale. However, the duration of the Famennian Age has been shortened from 15.3 to 13.3 million years in the new Gradstein et al. (2012) timescale, leading to a new estimate of 0.6 million years’ duration for each of the 22 Famennian conodont zones. As the Famennian Gap spanned ten of those zones, ten zones times 0.6 million-years-per-zone yields the new duration estimate of six million years for the Famennian Gap.
22. The duration of the Tournaisian Gap was once thought to have been some 14 million years—the duration of the entire Tournaisian Age in the Gradstein et al. (2004) timescale—and twice the duration of the original seven-million-year estimate of the duration of the Famennian Gap (see tables 6.2 and 6.7 in McGhee 2013). However, while McGhee (2013) was in press, Smithson et al. (2012) argued that the Tournaisian Gap (which they called Romer’s Gap) lasted for ten million years, not 14 million, before land vertebrate faunas began to recover from the Lilliput-effect small-body-size constraint imposed by “adverse conditions, such as aridity of other climatic conditions” (Smithson et al. 2012, 4535). It should be noted that this new ten-million-year estimate of the duration of the Tournaisian Gap is based solely on the land vertebrate fossil record and has yet to be corroborated by data from the marine fossil record and the land-plant fossil record, both of which were also affected by the climatic conditions of the Tournaisian Gap (see McGhee 2013, 184–188).
23. Additional geochemical similarities between the onset of the Cenozoic and Late Paleozoic Ice Ages also exist; for example, both the Miocene and Famennian glaciations were characterized by positive carbon-isotope anomalies of +0.8‰ δ13C and +1.2‰ δ13C, respectively (Zachos et al. 2001; Kaiser et al. 2006, 2016); oxygen-isotope increases of 0.3–1.0‰ δ18O and 0.8–1.2‰ δ18O, respectively (Flower and Kennett 1995; Kaiser et al. 2006); and estimated drops in sea-surface temperature of 6–7°C in the Miocene and at least 2–4°C in the Famennian, based on partial data (Shevenell et al. 2004; Kaiser et al. 2006). Likewise, both the Oligocene and proposed Frasnian glaciations were characterized by positive carbon-isotope anomalies of +0.8‰ δ13C and +3.0‰ δ13C, respectively (Zachos et al. 2001; Joachimski and Buggisch 2002); oxygen-isotope increases of 0.5–1.0‰ δ18O and 1.0–1.5‰ δ18O, respectively (Pusz et al. 2011; Joachimski and Buggisch 2002); and estimated drops in sea-surface temperature of 3–4°C in the Oligocene, based on partial data, and 5–7°C in the Frasnian (Wade et al. 2012; Joachimski and Buggisch 2002).
1. For a detailed examination of the aftermath of the Devonian extinctions, see McGhee (2013).
2. A lyginopterid spermatophyte, an extinct group of seed plants.
3. Lophophorate lophotrochozoans. Brachiopods still exist today, but in very low diversity in modern oceans.
4. Eutrochozoan lophotrochozoans.
5. It was originally argued that the Tournaisian Gap lasted 14 million years (McGhee 2013, 184–188), but a more recent estimate is ten million years (Smithson et al. 2012, 4535). For a more detailed discussion of the data, see note 22 in chapter 1.
6. For a detailed examination of the effect of the Devonian extinctions on the tetrapod faunas, see McGhee (2013).
7. For a detailed examination of the post-Tournaisian-Gap fauna, see McGhee (2013).
8. Tentative evidence from bone fragments (Daeschler et al. 2009) suggest that a whatcheeriid-like tetrapod may have been present in Pennsylvania, USA, in the latest Famennian. If true, this makes the enigma of the lack of further evolution in the family during the ten million years of the Tournaisian Gap even more perplexing.
9. Dated from the Lower crenulata through the isosticha conodont zones; see discussion in McGhee (2013, 196–199).
10. Possible further geochemical corroboration of this assessment is the documented presence of a large-magnitude positive anomaly in carbon-isotope ratios in strata dating from the middle Tournaisian in both North America and Europe. We saw in chapter 1 that the onset of glaciations in both the Late Paleozoic and Cenozoic ice ages was accompanied by positive carbon-isotope anomalies (see note 23 in chapter 1), and the mid-Tournaisian anomaly is “one of the largest known Phanerozoic δ13C events” (Saltzman et al. 2000).
11. Dated from the Upper commutata through the Middle bilineatus conodont zones; see discussion in McGhee (2013, 196–199).
12. The midpoint of the Visean, which spans in geologic time from 330.9 million to 346.7 million years ago, is 338.8 million years.
13. δ18O = 1.8‰ (Mii et al. 2001).
14. See Epshteyn (1981a), who argues that Ustritsky’s (1973) Early Permian (Sakmarian) glacial strata are Bashkirian-Muscovian in age.
15. However, the marine fauna of high-latitude regions did continue to experience fluctuations in extinction rates during the waxing and waning of glaciers during the Late Carboniferous; see the analysis of Balseiro (2016).
16. A United States quarter-dollar coin is 24 millimeters in diameter.
17. Benton (1989) documents the extinction of only four families of tetrapods in the Serpukhovian, and all four were of low species diversity.
18. See the extensive discussion of the evolution of amniotes, and of the evolution of flight in insects, in McGhee (2013).
19. Both are found in the famous Joggins tree-stump Lagerstätte in Nova Scotia, Canada; see discussion in McGhee (2013).
20. The question of the evolution of the first winged insects and their subsequent diversification becomes even more enigmatic if molecular analyses are included. Molecular phylogenies with divergence-date estimates have predicted the evolution of wings, hence the first Pterygota, to have occurred 406 million years ago in the Emsian Age of the Early Devonian (Misof et al. 2014)! If true, this would mean that insects possessing the key adaptation of wings still did not diversify and did not achieve large population sizes until the Bashkirian Age of the Late Carboniferous, some 83 million years later. Ecologically, that scenario does not make sense.
3. THE LATE CARBONIFEROUS ICE WORLD
1. Based on molecular phylogenies; see discussion in Bell et al. (2010).
2. Not all calamitean trees grew from rhizomes; see Rößler et al. (2012).
3. However, some cordaitean trees grew as tall as 30 meters; see Stewart (1983).
4. CO2 + H2O → CH2O + O2↑.
5. More precisely, the strata are dated to the Middle expansa conodont zone, the VH spore zone, and the Fa2c chronozone of older timescales; see McGhee (2013).
6. The late Robert Berner (1935–2015) did modify the Geocarbsulf model in a brief, three-page paper in 2009, bringing its predicted oxygen values closer to the older Rock-Abundance model. Still, the revised Geocarbsulf model predicts that oxygen levels did not increase to 30 percent or higher until the latest Carboniferous and, more significantly, actually predicts a lower oxygen content in the atmosphere in the Early Carboniferous than the original Geocarbsulf model! The Early Carboniferous is the same time interval in which animal gigantism evolved in numerous independent species lineages, a biological phenomenon that has been used to argue for a hyperoxic atmosphere on the Earth, as will be discussed in chapter 4.
7. Some peat fires do occur today in the tropics, during the dry season.
8. To help the reader, here is a rough correlation of some of the major older Carboniferous geologic time divisions with the modern time scale: Namurian A (pars) = Serpukhovian; Namurian A (pars), B, C, and Westphalian A, B = Bashkirian; Westphalian C, D, and Stephanian (Cantabrian pars) = Moscovian; Stephanian (Cantabrian pars) A, B = Kasimovian; and Stephanian C, Autunian (pars) = Gzhelian.
10. See also DiMichele et al. (2009, 210), in which differences in interpretation of the wettest part of cyclothemic rhythms are discussed—one interpretation holding that the wettest periods occurred during periods of sea-level lowstand, another holding that the wettest period occurred during sea-level highstand.
4. GIANTS IN THE EARTH …
1. Some have argued that Megarachne servinei was a giant land-dwelling eurypterid water scorpion, not a spider. If true, this would simply mean that this giant predatory arthropod was a merostome chelicerate rather than an arachnid chelicerate (table 4.1).
2. Giant arthropleuran fossils are reported from strata ranging in age from the Carboniferous Westphalian C [= Moscovian] to the Permian Lower Rotliegend [= Asselian].
3. Data from Clapham and Kerr (2012; supplemental tables S1, wing length, and S2, body width). Total wingspan is calculated by the formula: Wingspan = 2(wing length) + (body width).
4. The basal batrachomorphs are often called “temnospondyls” in the older literature, and the basal reptiliomorphs are called “anthracosaurs.” Both of these older taxonomic groupings are paraphyletic.
5. A United States quarter-dollar coin is 24 millimeters in diameter.
6. Specifically, the Cryogenian Period of the Neoproterozoic Era; see Erwin et al. (2011).
7. The most common symbionts are species of the dinoflagellate genus Symbiodinium; see table 4.3 for dinoflagellate evolutionary relationships.
8. Specifically, species in the fusulinacean families Neoschwagerinidae and Verbeekinidae; see discussion in McGhee et al. (2013).
9. For a discussion of the convergent evolution of ecological niches in Cenozoic mammals and Mesozoic dinosaurs, see McGhee (2011).
10. Named for the vertebrate paleontologist Everett C. Olson, who spent his life studying these vertebrates; Sahney and Benton (2008).
11. Specifically, eruption of the Emeishan Large Igneous Province in China, which we will examine in detail in chapter 6; see also McGhee et al. (2013).
12. These animals were the first of many vertebrate lineages to convergently evolve the ability to glide; see McGhee (2011).
13. These animals were the first of many vertebrate lineages to convergently evolve bipedalism; see McGhee (2011).
5. THE END OF THE LATE PALEOZOIC ICE AGE
1. See the paleogeographic map given in figure 5 of the paper by Isbell et al. (2016). However, these same authors argue that the region was ice free in the Permian.
2. See the new dating of the P3 and P4 glacial pulses given in Metcalfe et al. (2015).
5. Παν + γαια; see discussion of the tectonic effects of the assembly of Pangaea in chapter 3.
6. The Ophiacodontidae, Edaphosauridae, Eothyrididae, and Sphenacodontidae; see Kemp (2006).
6. THE END OF THE PALEOZOIC WORLD
1. LIP is pronounced like the word “lip,” and not spelled out L-I-P like an acronym.
2. The term “large igneous province” was introduced by Coffin and Eldholm (1991, 1994); see discussion in Saunders (2005). For comprehensive discussions of the LIPs that have occurred in geologic time, see Bryan and Ernst (2008) and Bryan et al. (2010).
3. A LIP geographic region sometimes also is called the “Traps,” as in the “Emeishan Traps.” The designation “trap” comes from “traprock,” an informal name commonly used by miners for basaltic rocks.
4. For extensive eyewitness accounts of this period of crisis in Europe, see tables A1 and A2 in Thordarson and Self (2003).
5. Some researchers have questioned the causal link between the Laki eruption and the abnormally cold winter of 1783–1784; see, for example, D’Arrigo et al. (2011); Lanciki et al. (2012). For a counterargument to these studies, see Schmidt et al. (2012).
6. (500 eruptions/100,000 years) × (20 km3 lava/eruption) = 10,000 km3 lava/100,000 years; 1,500,000 years/100,000 years = 15; thus 15 × (10,000 km3 lava)/ 15 × (100,000 years) = 150,000 km3 lava/1,500,000 years.
7. The degree of doming produced by the Emeishan super plume continues to be debated; Ukstins-Peate and Bryan (2008) argue that no doming at all occurred. For a detailed discussion of the debate, see Shellnutt (2013).
8. CH4 + 2O2 → CO2 + 2H2O.
9. For every molecule of CH4 oxidized, two molecules of O2 are removed from the atmosphere and one molecule of CO2 is released into the atmosphere; see note 8.
10. Families Neoschsagerinidae and Verbeedinidae; see Vachard et al. (2010).
11. Staffelids and schubertellids; see Vachard et al. (2010).
12. The Alatoconchidae; see Aljinović et al. (2008); Bond, Wignall, et al. (2010).
13. The model of Ganino and Arndt (2009) estimates a total emission of 78.4 to 162.4 trillion tonnes of CO2 into the atmosphere, based on the assumption of a 1 × 106 km3 LIP volume. Our current maximum estimates of the original Emeishan LIP volume are about a third smaller, at 0.6 × 106 km3. Thus I have reduced the original Ganino and Arndt (2009) CO2 injection-mass estimates by one-third.
14. The model of Self et al. (2005) estimates a total emission of 11.7 billion tonnes of SO2 into the atmosphere from a small LIP magma volume of 1.3 × 103 km3. Scaling this estimate up to an Emeishan LIP magma volume of 0.6 × 106 km3 results in a SO2 injection mass of 5.4 trillion tonnes.
15. 12CO2 + H2O → 12CH2O + O2.
17. The index is calculated as follows: δ13C = [(13C/12C)sample / (13C/12C)standard − 1] × 103, where values are reported as per mille (‰) relative to a standard. For many biostratigraphic studies, the standard taken is the isotopic ratio of a fossil belemnite from the Cretaceous Pee Dee Formation of the Carolinas, the “Pee Dee Belemnite” standard or simply δ13C(pdb).
19. Dolerite is a coarse-crystalline form of basalt formed at depth within the Earth.
20. The Olenekian Age is subdivided, from oldest to youngest, into the Dienerian, Smithian, and Spathian sub-ages; the highest temperatures occur in the Smithian (Sun et al. 2012).
21. Just as the photosynthetic process produces oxygen in the production of hydrocarbons, CO2 + H2O → CH2O + O2, the burning of those hydrocarbons consumes oxygen, CH2O + O2 → CO2 + H2O.
22. CH4 + 2O2 → CO2 + 2H2O.
23. The most general depletion cycle is Cl + O3 → ClO + O2, which destroys one ozone molecule (O3), and then ClO + O → Cl + O2, which simultaneously prevents atomic oxygen (O) from producing a new ozone molecule (O + O2 → O3) and produces a free chlorine atom to start the cycle all over again; see Beerling et al. (2007).
24. For contrast, humans see light in the 400 (violet) to 700 (red) nanometer spectrum.
25. In the timescale of Gradstein et al. (2012).
26. For example, in 1998 Bowring et al. narrowed the time interval down to 900,000 years, from 252.3 to 251.4 Ma; in 2004 Mundil et al. narrowed the time interval down to 400,000 years, from 252.8 to 252.4 Ma; and in 2011 Shen et al. narrowed the time interval down to 200,000 years, from 252.3 to 252.1 Ma.
28. However, it was at the University of Rochester in upstate New York that Jack Sepkoski collected most of the massive amount of data that he used in his analyses. For a brief glimpse into graduate student life and paleontological research conducted at the University of Rochester in those years, see McGhee (1996, 168–171).
29. For a detailed discussion of convergent ecological evolution, see McGhee (2011).
30. For an analysis of the differential fates of the rhynchonelliform brachiopods in the acidic oceans of the end-Permian, see Garbelli et al. (2017).
31. For an extensive discussion of the phenomenon of ecological convergence, see McGhee (2011).
32. The chitinozoans were the egglike reproductive phase of as yet unknown small invertebrate animals; see Grahn and Paris (2011).
33. Jack Sepkoski tragically died at age 50 in the year 1999.
34. For a discussion of the convergent evolution of swimming morphologies, see McGhee (2011).
35. The volaticotherians. For a discussion of the convergent evolution of flight morphologies, see McGhee (2011).
36. For a discussion of the convergent evolution of gliding morphologies in animals, see McGhee (2011).
37. Unfortunately, too late, as the predatory dinosaurs had already evolved at the beginning of the Carnian and diversified rapidly.
7. THE LEGACY OF THE LATE PALEOZOIC ICE AGE
1. The excess carbon dioxide is overwhelmingly the lighter isotope of carbon, 12CO2, which would be released by the burning of coal and other hydrocarbons. As we are not living at the end of the Permian, when coal strata and petroleum-rich strata were burned by mantle-plume magma (chapter 6), the only other source of large excesses of light-isotope carbon dioxide in the atmosphere is anthropogenic.
2. For a detailed examination of the process of the invasion of land by vertebrates, see McGhee (2013).
3. See the more extensive discussion of this evolutionary possibility in McGhee (2013).
4. For a more extensive discussion of the effects of the End-Frasnian Bottleneck, see McGhee (2013).
5. For a more extensive discussion of the effects of the End-Famennian Bottleneck, see McGhee (2013).
6. See the detailed paleogeographic map sequences in Blakey (2008).
7. See the detailed paleogeographic map sequences in Blakey (2008).
8. For an extensive discussion of the phenomenon of behavioral convergent evolution, see McGhee (2011).