09:00 〜 09:15
[BCG07-01] 大気酸素濃度の低下と生物の進化：危機進化説
キーワード：生命進化、原生代、生物多様性、真核生物、大気酸素濃度変動
The origin and evolution of Eukaryotes are key issues of biological evolution on the Earth. It is widely considered that the eukaryotes first appeared after the Huronian Snowball Earth event and subsequent Great Oxidation Event (GOE), and multicellular Eukaryotes, namely algae, emerged in the mid-Proterozoic. Because the Eukaryotes need aerobic respiration, it was considered that atmospheric oxygen (pO2) content was higher than the threshold of aerobic respiration, namely Pasteur point, through the Proterozoic (e.g. Kasting 1993; Lyons et al., 2014). Recently, the conventional view began to be reexamined (Lyons et al., 2021). For example, Cr isotopes of black shales suggest that the pO2 contents remained lower than the threshold (Planavsky et al., 2018), and triple-oxygen isotopes of lacustrine sedimentary rocks may also support the low pO2 condition (Planavsky et al., 2020; c.f. Liu et al., 2021). In addition, it is shown that even Metazoans can survive under the low pO2 condition (Mills & Canfield, 2014). On the other hand, high pO2 condition in the Proterozoic was also proposed based on iodine contents of carbonate minerals (e.g. Lu et al., 2018) and redox sensitive element contents of pyrites (e.g. Large et al., 2019). We present a review of secular change of pO2 contents and its influence on evolution of Eukaryotes.
The secular change of pO2 content through the Proterozoic is enigmatic. We compiled redox sensitive element (RSE) contents of black shales, iodine contents of carbonate rocks and Cr isotopes of carbonate rocks to estimate pO2 contents through the Proterozoic. The RSE contents of pyrites may be also proxies for the pO2 contents, but species of iron-bearing minerals are not used to estimate pO2 contents because species of iron-minerals can discriminate anoxic/euxinic events from oxic periods but cannot differentiate oxic events/periods from anoxic/euxinic events/periods. Mercury (Hg) isotopes have a potential to quantitatively estimate pO2 contents over 10-5 PAL in pO2 contents. Previous studies showed that the pO2 contents estimated from the abundances of RSEs such as Mo increased gradually or stepwise through the Proterozoic (e.g. Scott et al., 2008), but their abundances were actually fluctuated. In fact, other proxies also show that the pO2 contents were fluctuated through the Proterozoic, suggesting higher pO2 contents around 2.2, 1.5 and 0.8 Ga whereas lower around 1.7 and 1.2 Ga, respectively. On the other hand, molecular clock studies and paleontology suggest that appearance of the Eukaryotes, multicellular Eukaryotes (algae), and Alveolata/Rhizaria around 2.1-1.9 Ga, 1.7, and 1.2 Ga, respectively (Strassert et al., 2021; Baludikay et al., 2016; Javaux & Lepot, 2018).
Coevolution of organisms and the Earth is widely discussed (e.g. Williams & Da Silva, 2003), and coevolution of Eukaryotes and increase of pO2is often assumed in the Proterozoic (e.g. Condie & Sloan, 1998). However, the appearance of eukaryotes, namely symbiosis of aerobic bacteria within anaerobic archaea, occurred possibly in the high pO2 period whereas other evolutions occurred possibly in the low pO2 periods. Because their precursors, namely anaerobic Archaea and aerobic Eukaryotes, need anoxic and oxic environments, respectively, it seems inconsistent between the evolutions and environments. We would like to propose a new hypothesis, “The Crisis Evolution Hypothesis,” that the discrepancy became a driving force of evolution of the Eukaryotes, namely symbiosis, in the Proterozoic.
Baludikay et al., 2016. Precambrian Research 281, 166-184.
Condie & Sloan, 1998. Origin and Evolution of Earth: Principles of Historical Geology. Prentice Hall College Div, 498 pp.
Javaux & Lepot, 2018. Earth-Science Reviews 176, 68-86.
Kasting, 1993. Science 259, 920-926.
Large et al., 2019. Mineralium Deposita 54, 485-506.
Liu et al., 2021. Proceedings of the National Academy of Sciences 118, e2105074118.
Lu et al., 2018. Science 361, 174-177.
Lyons et al., 2014. Nature 506, 307-315.
Lyons et al., 2021. Astrobiology 21, 906-923.
Mills & Canfield, 2014. BioEssays 36, 1145-1155.
Planavsky et al., 2018. Emerging Topics in Life Sciences 2, 149-159.
Planavsky et al., 2020. Astrobiology 20, 628-636.
Scott et al., 2008. Nature 452, 456-459.
Strassert et al., 2021. Nature Communications 12, 1879.
Williams & Fraústo Da Silva, 2003. Journal of Theoretical Biology 220, 323-343.
The secular change of pO2 content through the Proterozoic is enigmatic. We compiled redox sensitive element (RSE) contents of black shales, iodine contents of carbonate rocks and Cr isotopes of carbonate rocks to estimate pO2 contents through the Proterozoic. The RSE contents of pyrites may be also proxies for the pO2 contents, but species of iron-bearing minerals are not used to estimate pO2 contents because species of iron-minerals can discriminate anoxic/euxinic events from oxic periods but cannot differentiate oxic events/periods from anoxic/euxinic events/periods. Mercury (Hg) isotopes have a potential to quantitatively estimate pO2 contents over 10-5 PAL in pO2 contents. Previous studies showed that the pO2 contents estimated from the abundances of RSEs such as Mo increased gradually or stepwise through the Proterozoic (e.g. Scott et al., 2008), but their abundances were actually fluctuated. In fact, other proxies also show that the pO2 contents were fluctuated through the Proterozoic, suggesting higher pO2 contents around 2.2, 1.5 and 0.8 Ga whereas lower around 1.7 and 1.2 Ga, respectively. On the other hand, molecular clock studies and paleontology suggest that appearance of the Eukaryotes, multicellular Eukaryotes (algae), and Alveolata/Rhizaria around 2.1-1.9 Ga, 1.7, and 1.2 Ga, respectively (Strassert et al., 2021; Baludikay et al., 2016; Javaux & Lepot, 2018).
Coevolution of organisms and the Earth is widely discussed (e.g. Williams & Da Silva, 2003), and coevolution of Eukaryotes and increase of pO2is often assumed in the Proterozoic (e.g. Condie & Sloan, 1998). However, the appearance of eukaryotes, namely symbiosis of aerobic bacteria within anaerobic archaea, occurred possibly in the high pO2 period whereas other evolutions occurred possibly in the low pO2 periods. Because their precursors, namely anaerobic Archaea and aerobic Eukaryotes, need anoxic and oxic environments, respectively, it seems inconsistent between the evolutions and environments. We would like to propose a new hypothesis, “The Crisis Evolution Hypothesis,” that the discrepancy became a driving force of evolution of the Eukaryotes, namely symbiosis, in the Proterozoic.
Baludikay et al., 2016. Precambrian Research 281, 166-184.
Condie & Sloan, 1998. Origin and Evolution of Earth: Principles of Historical Geology. Prentice Hall College Div, 498 pp.
Javaux & Lepot, 2018. Earth-Science Reviews 176, 68-86.
Kasting, 1993. Science 259, 920-926.
Large et al., 2019. Mineralium Deposita 54, 485-506.
Liu et al., 2021. Proceedings of the National Academy of Sciences 118, e2105074118.
Lu et al., 2018. Science 361, 174-177.
Lyons et al., 2014. Nature 506, 307-315.
Lyons et al., 2021. Astrobiology 21, 906-923.
Mills & Canfield, 2014. BioEssays 36, 1145-1155.
Planavsky et al., 2018. Emerging Topics in Life Sciences 2, 149-159.
Planavsky et al., 2020. Astrobiology 20, 628-636.
Scott et al., 2008. Nature 452, 456-459.
Strassert et al., 2021. Nature Communications 12, 1879.
Williams & Fraústo Da Silva, 2003. Journal of Theoretical Biology 220, 323-343.