Soil nutrient cycling
If we want to know more about how ancient nutrient cycles worked, we need to understand modern processes as best as we can. I have collected over 400 modern soils (from mostly North America) to study spatial and climatic trends in modern B horizons, which are the horizons typically used in paleoclimate or paleoenvironment reconstructions. Improving our understanding of modern nutrient cycles on land is also useful when thinking about how land use and fertility may shift under a changing climate.
In particular, I'm interested in potential relationships between the iron content of soils and regional climates/seasons, and how biological soil crusts (symbiotic desert communities of microbes, moss, and fungi) cycle phosphorus, an essential nutrient that's typically biolimiting in terrestrial ecosystems.
Modern soils with a range of iron oxides make a red and yellow rainbow!
Terrestrial early Earth
Thick mosses cover a recent volcanic landscape in Iceland. This scene stretches for miles and miles, making it easy to imagine a misty, primordial landscape!
The same nutrients that are important in terrestrial systems today were important two and a half billion years ago, too. I'm interested in constraining what these nutrients were doing - specifically, phosphorus and iron (and how they relate to the all-important carbon cycle). I'm also interested in how weathering has changed over time, delivering different amounts of nutrients to the oceans. Knowing how essential nutrients behaved is critical for reconstructing past oxygen levels and understanding the conditions in which early life evolved.
Speaking of early life...
By studying the chemistry of fossil soils (paleosols), we can look for signs of terrestrial life in the rock record - life that probably looked a lot like the biological soil crusts I also study. They leave chemical traces, called 'biosignatures,' in the soil, and this is what I look for in paleosols. These same terrestrial communities likely contributed oxygen; the question now is, how much?
Paleoclimate & paleoenvironments
We can also use these paleosols to reconstruct past climates and environments. Since soils form at the intersection of the biosphere, atmosphere, and the solid Earth, they provide a unique opportunity for us to understand what was happening right at Earth's surface. Using their chemistry, we can estimate how hot it was, how much it rained, what plants were growing in the soil, and even how much carbon dioxide and oxygen were in the atmosphere when they formed.
This type of reconstruction is of interest beyond academia - constraining how climate changed in the past is critical for understanding how the climate (and ecosystems) might change in the future.
The Little Grand Canyon in the San Rafael Swell area (near Green River, UT) is a great example of ancient terrestrial landscapes - check out the dark red, oxidized horizons!