Geocheminar - spring-2018

April 5, 2018
3:30 p.m. - 4:30 p.m.
Geology 3853

Presented By:

• Dr. Guillaume Avice - Caltech

Noble gases are excellent physical tracers and can answer fundamental questions regarding the origin and evolution of planetary atmospheres: i) What was the delivery mix (Solar/Chondritic/Cometary) to planetary atmospheres?; ii) To what extent are silicate portions of terrestrial planets degassed or preserved?; iii) How much of the atmosphere was lost by atmospheric escape and what is the timing of this escape? The study of the abundance and isotope composition of xenon ("xenology") in solar system materials helps to answer these fundamental questions. The goal of this talk is to explain why and how noble gas geo-/cosmo-chemists use xenon and to present recent results from space missions or Earth-based investigations.

April 12, 2018
3:30 p.m. - 4:30 p.m.
Slichter 3853

Presented By:

• Dr. Kingsley Odigie - UC Riverisde

Seminar Description coming soon.

April 26, 2018
3:30 p.m. - 4:30 p.m.
3853 Slichter

Presented By:

• Dr. Prasanna Naidu - UCLA
• Jeffrey Osterhout - UCLA

Jeffrey Osterhout: "Preservation of carbon isotopes in thermally altered organic microfossils: Implications for Earth's early biosphere" Dr. Prasanna Naidu: "Stable isotopes in water vapor and rainwater over Indian sector of Southern Ocean and estimation of the rainout fraction and the recycled moisture"

April 30, 2018
3:30 p.m. - 4:30 p.m.
Slichter 3853

Presented By:

• Myriam Telus - UCSC

Seminar Description coming soon.

May 10, 2018
3:30 p.m. - 4:30 p.m.
Schlichter 3853

Presented By:

• Dan Ibarra - Stanford University

Seminar Description coming soon.

May 17, 2018
3:30 p.m. - 4:30 p.m.
Schlichter 3853

Presented By:

• Jim De Yoreo - PNNL

Nucleation is the seminal process in the formation of minerals. Recent observations have revealed a rich set of hierarchical pathways of nucleation involving higher-order species ranging from multi-ion clusters to dense liquid droplets to transient amorphous or crystal-line phases. Despite their complexity, a holistic framework for understanding such path-ways based on classical concepts emerges when the effects of complexities in free energy landscapes and kinetic factors are considered. I illustrate that framework using in situ TEM and AFM studies on calcium carbonate, gibbsite and hematite. The results show that introduction of size-dependent phase stability or high driving force coupled with the exist-ence of metastable polymorphs leads to true two-step pathways characterized by the initial appearance of a bulk precursor. However, the introduction of surfaces that reduce the in-terfacial energy lead back to classical one-step pathways. On the other hand, introducing impurities that reduce molecular mobility can freeze in the metastable precursors for pure-ly kinetic purely reasons. Creation of micro-states representing local free energy minima likely stabilized by configurational factors also drives hierarchical pathways, but the in-termediates can only exist as transient microscopic entities. When high driving force cre-ates many nuclei, subsequent growth proceeds by interaction and coalescence of primary particles. Taken together, these findings provide a common basis for understanding the wide variety of nucleation pathways observed in mineral systems.

May 24, 2018
3:30 p.m. - 4:30 p.m.
Schlichter 3853

Presented By:

• Priya Ganguli - CSUN

Seminar Description coming soon.

May 31, 2018
3:30 p.m. - 4:30 p.m.
Schlichter 3853

Presented By:

Seminar Description coming soon.

May 31, 2018
3:30 p.m. - 4:30 p.m.
Slichter 3853

Presented By:

• Dr. Sarah Aarons - Univ. Chicago

Seminar Description coming soon.