Major impact events have shaped the history of Earth. Spherules ejected by these events reenter globally, heating and compressing the upper atmosphere. This work examines the chemical consequences of two types of major impacts. 1027 to 1029 J impacts during the Late Heavy Bombardment immediately predate the first evidence of life and produce HCN, which can form RNA nucleotides when gathered in surface water. NOx production from 1023 J impacts in a modern atmosphere can trigger massive algae blooms that affect marine life on a global scale.;To determine the chemical consequences of impact ejecta, this work models the atmospheric compression and heating as well as the resulting relaxation process using a two-phase flow solver. Combined with finite-rate chemistry, this work predicts the global chemical yield from the ejecta. We supplement this with the Direct Simulation Monte Carlo method to provide a correction for thermochemical nonequilibrium effects. We model the turbulent diffusion of the synthesized chemicals species and determine the rate of absorption into cloud moisture, resulting in a time accurate flux of chemicals into surface water.;This work then develops a compact model to predict the chemical yield and peak flux, based on ejecta properties. We stochastically model the Late Heavy Bombardment, and use this model to determine the likelihood of surface water chemical concentrations. Using this approach, we conclude the Late Heavy Bombardment would likely cause HCN polymerization in surface water with mixing depths below 100 m. Additionally, NOx yields above 2.5x10 13 moles can trigger global algae blooms in a modern atmosphere, and the Chicxulub event exceeded this threshold.
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