2014 Annual Science Report
Rensselaer Polytechnic Institute Reporting | SEP 2013 – DEC 2014
Project 5: The Environment of the Early Earth
This project involves the development of capabilities that will allow scientists to obtain information about the conditions on early Earth (3.0 to 4.5 billion years ago) by performing chemical analyzes of crystals (minerals) that have survived since that time. When they grow, minerals incorporate trace concentrations of ions and gaseous molecules from the local environment. We are conducting experiments to calibrate the uptake of these “impurities” that we expect to serve as indicators of temperature, moisture, oxidation state and atmosphere composition. To date, our focus has been mainly on zircon (ZrSiO4), but we have recently turned our attention to quartz as well.
Research on early-Earth environments over the reporting period has continued to focus on developing new tools (proxies) for extracting information from ancient minerals about crustal conditions and early atmospheres of Earth and Mars. The main accomplishments have been the following:
(1) Completion of a database on the trace-element composition of quartz as an indicator of crustal processes (97 different intrusive and extrusive rocks; 3000+ individual analyses).
(2) Preliminary evaluation of the aluminum content of zircon as a measure of the “aluminosity” of the medium in which this mineral crystallized (elevated Al in zircon suggests the presence clay minerals in precursor sediments).
(3) Experimental confirmation of the correlation of Al and H in quartz, which may form the basis for a hydrogen sensor.
(4) Completion of a study of Al diffusion in quartz, which allows ourselves and others to assess retention of this key indicator element in quartz over geologic time.
(5) Characterization of the Mg content of apatite as a function of temperature, which establishes a basis for determining the thermal history of this key host of the bioessential elements phosphorus and carbon.
(6) Characterization of nitrogen solubility and diffusion in quartz and olivine. These data not only provide essential insight into N cycling in the Earth but also create the potential to learn about early atmospheres from trapped N in crystal lattices. A preliminary report on this work was presented by Watson & Cherniak (Diffusion and solubility of nitrogen in olivine, Goldschmidt Conference abstract, Sacramento, June 2014).
(7) Measurement of the rate and quantity of carbon uptake in the common silicate minerals olivine and quartz. A preliminary report on this work was presented by Watson, Cherniak & Mergelsberg (Exploratory studies of 13C diffusion into olivine and quartz, Geol. Soc. Am. Annual Meeting abstract, Vancouver, October 2014).
(8) Development of simple equations describing the diffusive response of trace elements and isotopes to diffusion during heating. A preliminary report on this work was presented by Watson & Roberge (Diffusion on the prograde limb: progress and challenges, Geol. Soc. Am. Annual Meeting abstract, Denver, October 2013).
The early Earth geochemists (Watson group) also teamed up with the bio-analytical chemists (McGown group) to obtain the first data on RNA polymerization in synthetic analog systems of ocean-floor chimneys.
PROJECT MEMBERS:Bruce Watson
RELATED OBJECTIVES:Objective 1.1
Formation and evolution of habitable planets.
Earth's early biosphere.