Fall 2021

Tuesdays at 3:30 PM
Natural Science Annex 101


September 28, 2021

Speaker: Elizabeth Niespolo, Caltech

Title: 230Th/U burial dating of eggshells

Abstract: Many Pleistocene archaeological and paleontological sites beyond the c. 50-thousand-year 14C limit remain poorly constrained in age or undated entirely. Yet, they host key evidence about terrestrial ecosystems, the biological and cultural evolution of H. sapiens, and human geographic range expansion out of Africa. Many such deposits host giant avian eggshells, as large flightless birds producing giant eggs have resided on five continents in the Pleistocene and eggs served as a food source for foraging humans. Eggshells are furthermore made of calcite and are resistant to diagenesis in deep time, making them potential candidates for uranium-series (230Th/U) geochronology; however, eggshells do not have primary U in them, rendering conventional 230Th/U dating ineffective. Laser ablation measurements that compare modern and ancient avian eggshells indicate that while modern eggshells have negligible U, ancient eggshells host significant concentrations of U and Th that vary with the eggshells’ petrographic structures. I’ll share a novel approach to dating eggshells, first tested with ostrich eggshells, called 230Th/U “burial dating”, which explicitly accounts for U in ostrich eggshell acquired from soil pore water. U and Th concentration profiles from laser ablation data optimize subsampling approaches to correct for post-depositional U uptake, and 232Th/U profiles allow screening to avoid “dirty” samples that may produce imprecise, inaccurate 230Th/U ages. Careful subsampling and the use of a simple model of U uptake provide reliability criteria inherent to the U-Th data to determine accurate 230Th/U burial ages. Resultant 230Th/U burial ages of ostrich eggshells from African archaeological sites preserve stratigraphic order and agree with independent dates. In other avian eggshells, laser ablation data suggest primary petrographic structures control secondary uptake of U, indicating that 230Th/U burial dating may apply to well-preserved eggshells of other avian taxa.

sd

Host: Tamara Pico


October 5, 2021

Speaker: Philip Pogge Von Strandmann, University of Mainz

Title: Why does the Earth stay habitable?

Philip

Host: Will Rush


October 12, 2021

Speaker: Noam Izenberg, Johns Hopkins University

Title: The New Decade of Venus Exploration

Abstract: The coming decade will see a veritable armada of spacecraft arrive to explore mysteries that have only become more compelling since the early days of the planet’s exploration. The Venus science community has a huge laundry list of questions about the second planet that has only grown since Magellan, the last US mission to visit. What science we can do at Venus has also changed over the decades. Venus, while still a uniquely harsh place, is more obtainable than ever. The next major missions: DAVINCI, and VERITAS from NASA and EnVIsion from ESA will fundamentally change what we know about Venus, its evolution, its relationship to earth, and its place as a representative terrestrial exoplanet. The Three goals that have guided prospective missions to Venus in recent years include 1) Understanding Venus’ early evolution and potential habitability to constrain the evolution of Venus-like worlds. 2) Understanding the atmospheric dynamics and composition on Venus. And 3) Understanding the geologic history preserved on the surface of Venus and the present-day couplings between the surface and atmosphere. The three upcoming major missions will address major components of all three of these goals, and pave the way for more. This talk will dive deeper into the open questions for Venus, and how each of the upcoming missions hopes to answer them, along with snapshots of other upcoming Venus investigations and the possibilities of the future.

Host: Rachel Maxwell


October 19, 2021

Speaker: Andrea Dutton, University of Wisconsin-Madison

Title: Sea level of the past and future: At the Intersection of Politics, Race, Gender, Ice Sheets, and Corals

Host: Jim Zachos

Andrea


October 26, 2021

Speaker: Andrew Gunn, Stanford

Title: Wind-blown dunes in the solar system

Andrew

Host: Xinting Yu


November 2, 2021

Speaker: Jean E. Moran, CSU East Bay

Title: Extrinsic Tracers in Hydrology

Jean

Host: Emillio Grande


November 9, 2021

Speaker: Sarah Arveson, Berkeley

Title: Melting and Mixing at Extreme Pressures: Layered Liquids in Earth’s Outer Core?

sarah

Host: Jasmeet Dhaliwal


November 16, 2021

Speaker: Scott McCoy, University of Nevada-Reno

Title: Rainfall-intensity thresholds for post-wildfire debris-flow initiation vary with climatology of peak rainfall intensity

Abstract: Rainfall-intensity thresholds for post-wildfire debris-flow initiation are the primary criteria for issuing debris-flow hazard warnings in burned landscapes. Yet, with the expansion of frequent wildfires into a wide range of hydroclimates, there is a growing need for accurate thresholds in landscapes with few to no observations of post-fire debris-flow activity on which to constrain them (such as in Northern California and the Pacific Northwest). To help constrain thresholds in these burned landscapes, I will present fire-scale observations of rainfall intensities associated with post-wildfire debris-flow initiation across the western US that indicate rainfall-intensity thresholds for post-fire debris-flow initiation are systematically higher at sites that frequently experience higher maximum rainfall intensities. In particular, there is a strong correlation between the 15-minute rainfall-intensity threshold and the peak 15-minute rainfall intensity of storms with a one-year return interval. In the second part of the talk, I will explore a growing dataset of soil properties measured in burned landscapes across a range of hydroclimates and propose some physical mechanisms that help explain such a correlation.

Scott

Host: Noah Finnegan


November 23, 2021

Speaker: Daniel Koll, Peking University

Title: From Earth to Rocky Exoplanets and back

Abstract: Our galaxy is full of Earth-sized, potentially Earth-like, planets, yet we still barely know what these planets are actually like. I will use several examples to show how the rapid exploration of exoplanets offers unique opportunities for Earth Science, and how exoplanets are in turn helping us better understand Earth. Examples include how potential intensity theory from tropical meteorology played a key role in interpreting the first temperature map of a nearby super-Earth, how similar measurements promise to tell us whether the average Earth-sized exoplanet in our galaxy is an airless bare rock (like Mercury), and how Earth's persistently-linear radiative balance shapes our planet's future under global warming.

Daniel

Host: Nicole Feldl


November 30, 2021

Speaker: Mark England, UCSC

Title: Arctic climate change: the role of greenhouse gases, aerosols and ozone depleting substances

Mark

Host: Nicole Feldl