Geoscience Reference
In-Depth Information
Figure 2.18 Cenozoic p CO 2 for the period 0 to 65 million years ago. Data are a
compilation of marine (C isotopic composition of alkenone biomarkers and boron
isotopic compositions of foraminifera) and lacustrine mineralogical records. The
dashed horizontal line represents the maximum p CO 2 for the Neogene (Miocene to
present) and the minimum p CO 2 for the early Eocene, as constrained by calculations
of equilibrium with Na-CO 3 mineral phases (vertical bars, where the length of the
bars indicates the range of p CO 2 over which the mineral phases are stable) that are
found in Neogene and early Eocene lacustrine deposits (Lowenstein and Demicco,
2006). SOURCE: Zachos et al. (2008).
How Have Climate, Life, and Biogeochemical Cycling Interacted Through
Time?
The deep-time geological record documents the magnitude over which the
physical, chemical, and biological attributes of the ocean, continents, and atmosphere
have varied over the history of Earth. There is little debate that microbial life and
plant life have played a fundamental role in the evolving atmospheric concentrations
of O 2 and CO 2 , but the specifics of this interplay remain highly controversial.
Tectonically driven changes in degassing and continental weathering are also
fundamental, especially with respect to geologically transient but biologically
devastating greenhouse gas increases such as during mass extinction and ecosystem
reorganization events, notably those at the end-Permian, end-Triassic, Cretaceous-
Paleogene, and PETM. However, it remains to be understood how new life forms
changed the nature of elemental cycling (O, C, N, S), or how long-term changes in
geochemical cycling have influenced the evolution of new life forms. Similarly, the
oceans have fluctuated from periods of minimal oxygenation to conditions
comparable to the well-ventilated ocean bodies of today. In addition to gradual, long-
term shifts in baseline conditions, the oceans have at times experienced rapid
Search WWH ::




Custom Search