Carl B. Pilcher, Interim Director
NASA Astrobiology Institute
Abstract: Earth has been not just a habitable/inhabited planet for the last 4 billion years or so. When viewed as an exoplanet, Earth has been in effect a series of planets--different pale blue dots, a pale orange dot, a pale white dot, etc.—each in a different biogeochemical state presenting different characteristics to an observer in a distant star system. In this talk I’ll review our knowledge of Earth’s biogeochemical state over time, focusing on epochs in Earth’s history when it would have appeared different from the pale blue dot of today. These variations in Earth’s observable characteristics over time need to be part of our thinking as we develop the capacity to characterize potentially habitable exoplanets.
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