Aug 25 – 27, 2021
Online
Europe/Berlin timezone

Photons, electrons, and chemistry in muddy lakes

Aug 25, 2021, 3:25 PM
25m
Online

Online

Due to unstable situation with Covid-19 the event will be held online!

Speaker

Dimitar Sasselov (Harvard University)

Description

It is plausible that the Hadean Earth had less sub-aerial land, yet it still had an enormous number of shallow water lakes, often in closed basins, and often in association with hydrothermal fields. The N2-CO2-H2O atmosphere was likely neutral or weakly reduced (with minor CO and H2), except for short periods after major impacts capable to briefly reduce the atmosphere. Episodic drying of the shallow water basins would lead to accumulation (and burial) of a variety of salts. These include metallo-cyanides like cyanocuprate and ferrocyanide, thanks to trace amounts of HCN from lightning and meteoritic reprocessing of the atmosphere. It appears that very significant deposits of ferrocyanide would accumulate in a 1000 years or less.
This presentation describes a number of experiments aimed at understanding the redox stratification and photochemistry in the shallow water column exposed to solar UV light. The irradiations were limited to the UVC and UVB range, as atmospheric CO2 would have cut off all solar UV flux below 205 nm. In addition to broadband UV lamps, we used a tunable laser pump-probe system to perform ultrafast transient spectroscopy, taking care to use astrophysically and geochemically plausible fluxes and concentrations. Our aim is to elucidate the photodynamic mechanisms of hydrated electron production and chemistry, as well as the selectivity and stability of the products, e.g. nucleotides and their oligos.

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