The Biosphere
Originally introduced by the Austrian geologist Eduard Suess, the concept of the biosphere was first fully articulated by the Russian biogeochemist Vladimir Vernadsky. In Vernadsky’s view, the biosphere is a planetary mechanism whereby life, in its harnessing and processing of solar radiation, transforms and transports the material-energetic makeup of Earth’s surface environment. Vernadsky’s biosphere is more than the sum total of Earth’s organisms, or the totality of Earth’s ecosystems — it is a process, a realm of activity, the layers of the Earth perpetually reworked and reshaped by life. As Lynn Margulis and Dorion Sagan wrote, “…Vernadsky did for space what Darwin had done for time: as Darwin showed all life descended from a remote ancestor, Vernadsky showed all life inhabited a materially unified place, the biosphere.”
This photograph, titled Earthrise, was taken from lunar orbit on December 24th, 1968 by Apollo 8 astronaut Bill Anders, one of the few humans to have left the biosphere (by bringing small pockets of it with him). Image credit: NASA
Biospheric Evolution
The biosphere has evolved in at least three discrete stages, each one corresponding to one of the three main eons of the geologic timescale: the Archean, Proterozoic, and Phanerozoic. Every stage is marked, on average, by global environmental stability — a distinct steady state for the Earth system. Each transition from one eon to the next was characterized by global environmental change and evolutionary innovation — abrupt and tumultuous punctuations to the biospheric order. These biospheric revolutions, in setting the stage for the next eon, irreversibly destroyed the conditions of the previous one. The Archean-Proterozoic transition, for instance, was marked by the permanent oxygenation of the atmosphere and hydrosphere, ultimately driven by the origin of photosynthetic oxygen production. This transition destroyed the oxygen-free conditions of the Archean biosphere, and set the stage for the low-oxygen world of the Proterozoic. Determining how global environmental change (e.g. atmospheric oxygenation) affords new opportunities for biological evolution, and how evolutionary innovation (e.g. the origin of oxygenic photosynthesis) adds new stressors and feedbacks to the global environment, lies at the heart of historical geobiology, the study of the co-evolutionary relationships between Earth and life over time.
The Geologic Time Spiral, highlighting the procession of macroscopic plant and animal forms over the course of the Phanerozoic, the current evolutionary stage of the biosphere. Image credit: USGS