You’ve now read and thought a little about some pretty big problems: Hotspots, mantle plumes, supercontinental cycles, the rise of oxygen and the emergence and persistence of complex life on Earth. You’ve also learned a little about Mars: Although there is some evidence of similar surface processes to Earth certainly early in the planet’s history (volcanism, glaciers, rivers), Mars has evolved very differently. One obvious difference is that whereas Earth has maintained a comfortable and stable climate over much of its 4.6 billion year history, Mars went through a climate collapse sometime during its evolutionary adolescence.
A crucial difference between Earth and Mars and a major reason for present day differences between the two planets is that Earth has plate tectonics and Mars does not (and probably never did). The significance of this difference in tectonic regime cannot be understated. Plate subduction, for example, drives accretion, mountain building, precipitation and chemical weathering at the edges of continents, as well as arc volcanism. Taken together, these processes govern about half of Earth’s long-term carbon cycle and act to enforce a temporally stable climate. The subduction and stirring into the mantle of rocks in contact with the atmosphere and oceans also delivers cooling and volatiles back into Earth’s deep interior. This recycling is, indeed, key to Earth’s remarkable habitability.
So, how do we know any of this recycling is actually happening? One way of exploring deep connections between the surface and the deep interior is to investigate what mantle plumes carry to the surface in the form of erupted lavas as a result of their rise from the core-mantle boundary region through 3000 km of Earth’s mantle. In this module you will read a couple of more challenging papers on this topic. Cabral et al. uses a clever sulfur isotopic signal to identify the fingerprint of the modern atmosphere in the source region for mantle plumes. Weis et al. use a different fingerprinting strategy to show that the plume source region may indeed contain the dregs of sub ducted slabs, but that this signature is only part of a rich story influenced by the full history of Earth’s formation and tectonic evolution.
Learning Goals for This Module (TBA)
Video: How does “Mass-dependent” stable isotope fractionation work? (Watch this if basic isotope fractionation is new to you)
Introduction
Reading 1: The story of Earth’s Early Oxygen Rise
Mass-independent fractionation: A summary report
Domagal-Goldman et al. (Read text and Figures THROUGH FIGURE 4)
“Mass-independent fractionation (MIF)” of sulfur isotopes and the rise of atmospheric oxygen: A short review (required)
Kump
A lucky discovery of “MIF-Sulfur”: the “catastrophic” rise of atmospheric oxygen and its effects on Earth’s early sulfur cycle (required)
Farquhar et al.
A more complete story about Earth’s oxygen rise 14 years after the remarkable discovery of MIF-sulfur (Not required but I would read this for the context during the week)
Lyons et al.
Reading 2: A fingerprint for an oxygen-rich atmosphere appears in lavas erupted in Polynesia that are related to a mantle plume
Mantle plumes and plate tectonics: Is Earth’s atmosphere really stirred into the mantle? How long does it take to do this?
Cabral et al.
Reading 3: (time-permitting) A fingerprint for the structure of the core-mantle boundary region from which mantle plumes rise
Mantle plumes and plate tectonics II: If subducting slabs get to the core-mantle boundary, what else is down there and how do we know? What is the structure of Earth’s deepest mantle?
Weis et al.
