In this section we introduce what isotope systematics tell us about how our solar system and the earth are formed, and about the timing and nature of the processes involved. We discuss what isotopes tell us about the early history of the earth and its evolution and its structure, and of the formation of the moon, the atmosphere, and the oceans. We then talk about cosmogenic isotopes and how they are used to constrain recent and current processes on the earth’s surface.
Related links are listed below the table. Lecture notes are provided by WHOI and link away from OCW. Select lecture slides are available.
| SES # | TOPICS | SUMMARIES | SLIDES |
|---|---|---|---|
| 7 | Solar System and Planetary Formation | We briefly discuss timescales of the universe, stellar nucleosynthesis, and solar system formation, mostly from the perspective of long-lived radionuclides (Problem Set 1). Before we talk about the formation of Earth and Moon, we cover the concept of volatility (half-condensation temperatures) and the partitioning of elements between different phases (lattice strain model), a pre-requisite for understanding the differentiation of our planet. A brief introduction to meteoritics will lead to the discussion of timescales of differentiation, mainly from the perspective of extinct radionuclides (26Al-26Mg, 182Hf-182W) with the use of the 207Pb/206Pb system as an absolute time anchor. We end with the widely accepted scenario for the formation of the moon, and discuss its timing in the context of the 182Hf-182W extinct radionuclide system. | |
| 8 | Earth Structure and Evolution | Given the timing and nature of the formation of the earth/moon system (especially using extinct radioactivities), we now effects of heat-producing radionuclides on the earth’s evolution and structure (including mantle structure, seafloor spreading, and continent formation), and the more recent constraints on the earth’s composition afforded by isotopes and geoneutrinos. We will learn about parent-daughter fractionation associated with geochemical processes (e.g., melting, metasomatism, crystallization). Finally, we explore how isotopes have shed light on the existence of natural nuclear reactors in the past. | Lecture 8 Notes (PDF) |
| 9 | Atmosphere-Ocean Formation | The formation of the oceans and atmosphere likely occurred early in the earth’s history. We discuss the isotopic evidence for the timing of these events and on how isotope patterns are reflecting current earth structure, the relationship between the earth and other planets, and possible ongoing terrestrial degassing. We also investigate the fact that for some gas isotopes, the atmosphere is not a closed system, but is still evolving on the mega- to giga-year time-scales. | Lecture 9 Notes (PDF) |
| 10 | Cosmogenic Isotopes I | The earth has in the past been, and continues to be, bombarded with high-energy cosmic rays. These cosmic rays interact with the atmosphere and surface earth to produce isotopes that in turn prove useful for constraining processes occurring on or near the earth’s surface. We explore the nature of these isotope systems and their application to studying recent and current earth processes. | Lecture 10 Notes (PDF) |
| 11 | Cosmogenic Isotopes II | One cosmogenic isotope, radiocarbon, holds a special place in isotope geochemistry. Knowing its past abundance in the atmosphere in the ocean is key to (a) establishing chronology over the past ~50,000 years (radiocarbon dating), (b) understanding past changes in cosmogenic production rates, and (c) diagnosing recent past changes in the carbon cycle. We explore all these three aspects in considerable detail here. | Lecture 11 Notes (PDF) |
| 12 | Problem-Solving Session 2 | Here we embark on a tutorial on model building: a box model of cosmogenic isotope systems, radiocarbon, and the carbon cycle. |
Related Links
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CosmoCalc Website
An Excel Spreadsheet add-in for cosmogenic production rates in time/space including instructions and documentation. -
Moon-forming impact
A simulation (by Robin Canup) of the impact of Mars-size Theia with the proto-Earth (accreted to about 80% of its current size). The formation of the Moon from the debris circling Earth is not shown, but is a well-understood process that took only about a day. -
14 billion years ago
The trailer to “The Big Bang Theory”—watch the first 6 seconds frame by frame—it’s actually quite accurate. The later time axis is pretty distorted (animals emerging from the sea at 11000 BC, dinosaurs roaming the Earth 8000 BC, etc).
