Although this class won't aim to provide a comprehensive and rigorous treatment of the subject, we will need to develop some background knowledge and master some geochemical jargon in order to progress at all. One of the best resources available is the online textbook "Geochemistry" by William M White (well, what else would you call it?). This is arguably the best and most comprehensive text ever written on the subject. Certainly the best yet-to-be-pulished one. It is intended as a specialist, graduate-level text and takes a fairly rigorous approach, but most chapters start from a non-specialist level, and reward perseverance. We will dip into it occasioanlly for background reading.
Topic 1: Geochemical clues to the Hadean
Main paper: Harrison T.M. The Hadean Crust: Evidence from >4Ga Zircons. Ann. Rev. Earth Planet. Sci. 37, 479-505, 2009.
Topic 2: Evolution of Earth's atmosphere
Main paper: Kasting J.F. and Catling D. Evolution of a Habitable Planet. Ann. Rev. Astron. Astrophys. 41, 429-463, 2003.
Also, supplementary reading on the oxygenation of the atmosphere ... Catling D. and Claire M.W. How Earth's atmosphere evolved to an oxic state. A status report. Earth Planet. Sci. Lett. 237, 1-20, 2005.
More useful papers, not yet linked, are here.
Topic 3: You are what you eat ... stable isotopes and diet
Unfortunately the abstract which launched this field of research doesn't appear to be available online, but if you'd like to chase a paper copy, the reference is:
DeNiro M.J. and Epstein S. (1976) You are what you eat (plus a few permil): the carbon isotope cycle in food chains. Geological Society of America Abstracts with Programs 8: 834-835.
To get started we'll read the first and signature paper in this field: DeNiro M.J. and Epstein S. (1978) Influence of diet on the distribution of carbon isotopes in animals. Geochim. Cosmochim. Acta 42, 492-506.
For additional background, the corresponding paper about nitrogen isotopes is: DeNiro M.J. and Epstein S. (1981) Influence of diet on the distribution of nitrogen isotopes in animals. Geochim. Cosmochim. Acta 45, 345-351.
To explore some applications of these ideas, please read at least one of the following:
Records of Pacific salmon populations from nitrogen isotopes: Finney B. et al. (2000) Impacts of Climatic Change and Fishing on Pacific Salmon Abundance Over the Past 300 Years. Science 290, 795-799.
What did Neanedrthals eat? Richards M.P. et al. (2000) Neanderthal diet at Vindija and Neanderthal predation: The evidence from stable isotopes. PNAS 97, 7663-7666.
What did cave bears eat (when not eating neanderthals)? Hilderbrand G.V. et al. (1996) Use of stable isotopes to determine diets of living and extinct bears. Can. J. Zool. 74, 2080-2088.
Dietary records from analyses of hair ... Cerling T.E. et al. (2006) Stable Isotopes in Elephant Hair Document Migration Patterns and Diet Changes. PNAS 103, 371-373.
Carbon isotopes in paleosol carbonate, C4 photosynthesis and the rise of grasslands ... Cerling T.E. et al. (1993) Expansion of C4 ecosystems as an indicator of global ecological change in the late Miocene. Nature 361, 344-345.
Topic 4: More on stable isotopes, focusing on temperatures and climate records
The idea of using oxygen isotope ratios to measure past temperatures goes back to Harold Urey and Sam Epstein in the late 1940s and early 1950s. Here are the original papers on the carbonate paleotemperature scale: The first includes a lot of detail on laboratory methods; the second made procedures more precise and practical, setting in motion vast amounts of subsequent research. Figure 9 in the second paper is a classic of geochemistry.
Trace element concentrations in carbonate shells are also sensitive to the temperature of the water in which the shell grew. Trace element measurements are particularly useful when coupled with stable isotopes, as shown in this review of climate records derived from long-lived corals.
Topic 5: Heterogeneity of the mantle, and its geodynamic significance
Although convection and flow in the mantle must gradually mix and homogenize its chemical and isotopic composition, geochemists have found evidence of widespread heterogeneity. Now the game is to determine what processes produce chemical variation in the mantle and how long it can survive. The questions that arise have great significance for understanding planetary processes and evolution. For instance - have 'primitive' parts of the mantle survived since the Earth's early history, and if so, what is their composition? Is convection of the mantle layered? Has the whole mantle been depleted by formation of the crust, oceans and atmosphere, or just a part of it? Does crustal material get recycled into the mantle by subduction? What about volatile elements like hydrogen and carbon, crucial to the origin and support of life? And so on.
A good statement of the problem, data and interpretations is given in a review paper by Hofmann.
This contains a glossary to help with some of the geochemical jargon, but for help you can also turn to White's online textbook "Geochemistry". Chapter 8 on radiogenic isotope geochemistry will be the most useful; section 8.4 contains specific information on the isotope systems referred to in Hofmann's paper.Two good follow-up papers are:
(i) van Keken et al., Ann. Rev. Earth Planet. Sci. (2002), which focuses on the interesting isotope He-3.
(ii) Jackson et al., Nature (2007), which reports an isotopically extreme data set from Samoa. An important aspect of this subject is why so much of the data comes from oceanic islands. We will also consider why geochemists tend to focus on exotic tropical islands like Hawaii and Samoa, rather than cold and miserable ones like Gough, Bouvet and Kerguelen ...
Here are the specialist papers for group presentations:
(i) Early He isotope work by Mark Kurz and others revealed that some ocean islands were marked by very high He-3/He-4 ratios, but others showed the opposite trend. This is the original Nature paper. Much of what has been discovered since is described in the first few pages of van Keken et al., Ann. Rev. Earth Planet. Sci. (2002). The remainder of the paper is interesting, but goes further than we'll have time for in class.
(ii) Trace element measurements reported in this paper by Hofmann et al. prompted re-consideration of mantle models which up to that time had been based almost entirely on isotopic data. I suggest focusing on the central message about the difference between crustal trace element ratios and those in all oceanic lavas, and its implication for the complementary relationship between mantle and crust.
(iii) A great deal of isotopic work has tried to determine the history of crustal growth, and resolve the question of whether the continents have grown progressively through time, or a longstanding crustal mass has been continuously recycled through time. As we learned from arguments presented in the first topic we dealt with most of the results turn out to be ambiguous. This paper on the Nd isotopic composition of river sediments and airborne dust comes up with some credible constraints, as well as information about the mean age of sediments and sedimentary rocks. Focus on sections 4.1 - 4.3, and 4.5 in particular.
Optional reading - worth a look: Once you wade through all the isotopic and trace element taxonomy, this topic is really all about the geodynamic processes involved in heat transport from the Earth's interior - spreading-ridge volcanism, subduction and the ascent of mantle plumes - and the plate tectonics that results. A good background paper on plumes, and their role in more than just ocean-island volcanism, is: Campbell and Griffiths (1990) Implications of mantle plume structure for the evolution of flood basalts. Earth Planet. Sci. Lett. 99, 79-93.
Topic 6: Mountain building, global climate and the Sr isotope record in seawater
Yes - they're all connected. That's the magic of geochemistry. Two short papers to read for this week:
(i) This one demonstrates how the Sr isotope composition of seawater through the last 100 Myr relates to global weathering and plate tectonic processes Edmond (1992) Himalayan tectonics, weathering processes and the Sr isotope record in marine limestones.
(ii) Whereas this one connects the same processes of weathering and mountain building to climate and the carbon cycle: Raymo & Ruddiman (1992) Tectonic forcing of late Cenozoic climate.
In addition, read one of:
(a) The section on carbon isotopes in marine fossils (Section 7) in Veizer et al. (1999). The rest of the paper provides an interesting review and data summary, but we will be interested in whether the history of carbon isotopes in seawater can be used to analyze feedbacks in the weathering/CO2 cycle.
(b) The comment, and the comment and reply between Bickle, Berner and Caldeira. This is a useful discussion of sources, sinks and feedbacks in the long-term carbon cycle.
(c) The now famous "chicken or egg" paper by Molnar and England, which aimed to turn the tectonics and climate argument on its head.
That's it.
