Читать книгу Earth Materials онлайн

101 страница из 155

In the mid‐nineteenth century, scientists recognized a rapid change in mammalian fossils that occurred early in the Tertiary era. The earliest Tertiary epoch, named the Paleocene (early life), was dominated by archaic groups of mammals that had mostly been present during the preceding Mesozoic Era. The succeeding period, marked by the emergence and rapid radiation of modern mammalian groups, was called the Eocene (dawn of life). The age of the Paleocene–Eocene boundary is currently judged to be 55.8 Ma. Later workers noted that the boundary between the two epochs was also marked by the widespread extinction of major marine groups, most prominently deep‐sea benthic foraminifera (Pinkster 2002; Ivany et al. 2018). The cause of these sudden biotic changes initially remained unknown. Oxygen and carbon isotope studies have given us some answers.

Kennett and Stott (1991) reported a rapid rise in δ¹⁸O at the end of the Paleocene, which they interpreted as resulting from a rapid rise in temperature, since they believed that no prominent ice sheets existed at this time. Subsequent work (e.g., Zachos et al. 1993; Rohl et al. 2000; Gehler et al. 2016; Ivany et.al. 2018) has confirmed that temperatures rose ~6–8 °C at high latitudes and ~3–5 °C at low latitudes over a time interval not longer than 10 000 years. Rapid global warming, in this case the Paleocene–Eocene thermal maximum (PETM), has apparently occurred in the past, with significant implications for life on Earth. Researchers have also shown that the higher temperatures lasted for approximately 100 Ka (Pinkster 2002; Ivany et al. 2018). How long will the current period of global warming last?