Alternative Earths Astrobiology Center


Four critical intervals of Earth’s inhabitation


Alternative Earth 1

Atmospheric Traces of Oxygenic Photosynthesis
mid-late Archean | 3.2 to 2.4 billion years ago (Ga)

Primary Objective—Determine when oxygenic photosynthesis first left traces in Earth’s atmosphere. More specifically, we will investigate the reasons behind a hypothesized temporal lag between the initial onset of biological oxygen production and the significant accumulation oxygen in the atmosphere.

Alternative Earth 2

Dramatic Oxygen Fluctuations
mid-Paleoproterozoic | roughly 2.3 to 2.0 billion years ago (Ga)

Primary Objective—Determine whether Earth’s surface underwent a unidirectional oxygen rise—as typically envisioned—or was this early history characterized by a series of rises and falls. We will test the idea that mid-Paleoproterozoic was characterized by near modern oxygen levels followed by a dramatic oxygen crash, with major implications for the Earth’s climate system and as a prelude to the emergence of complex life much later.

Alternative Earth 3

Oxygen Stasis and the Rise of Eukaryotes and Metazoans
mid-Proterozoic | 1.8 to 0.8 billion years ago

Primary Objective—Determine whether surface oxygen levels were low enough to play a direct role in controlling when animals first emerged and diversified. We will specifically test whether there were intervals in this time period marked by very low atmospheric oxygen levels, as suggested by our preliminary data. More generally, we will explore the overarching redox/nutrient/biotic balance during this important middle chapter of Earth history marked by the restrained emergence of complex life.

Alternative Earth 4

The Rise of Complexity Amid Environmental Turmoil
Late Proterozoic | 0.8 to 0.5 billion years ago

Primary Objective—Determine the relative roles that biological innovation and environmental change played in reshaping Earth’s ecosystems, atmospheric composition, and climate during the early stages of the rise of complex life. Specifically, our goal is to determine whether the diversification of complex life was a major driver of shifts in Earth’s oxygenation and of major climate perturbations, including Snowball Earth Events.

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