The Story of Earth: How Life and Rocks Co-Evolved

 Dr. Robert Hazen, Carnegie Institution for Science, Geophysical Laboratory:

The story of Earth is a 4.5-billion-year saga of dramatic transformations, driven by physical, chemical, and—based on a fascinating growing body of evidence—biological processes. The co-evolution of life and rocks, the new paradigm that frames this lecture, unfolds in an irreversible sequence of evolutionary stages. Each stage re-sculpted our planet’s surface, each introduced new planetary processes and phenomena, and each inexorably paved the way for the next. This grand and intertwined tale of Earth’s living and non-living spheres is only now coming into focus. Sequential changes of terrestrial planets and moons are best preserved in their rich mineralogical record. “Mineral evolution,” the study of our planet’s diversifying near-surface environment, began with a dozen different mineral species that formed in the cooling envelopes of exploding stars. Dust and gas from those stars clumped together to form our stellar nebula, the nebula formed the Sun and countless planetesimals, and alteration of planetesimals by water and heat resulted in the approximately 250 minerals found today in meteorites that fall to Earth. Following Earth’s growth and separation into the core, mantle, and crust, mineral evolution progressed by a sequence of chemical and physical processes, which led to perhaps 1500 mineral species. According to some origin-of-life scenarios, a planet must evolve through at least some of these stages of chemical processing as a prerequisite for life. Once life emerged, mineralogy and biology co-evolved, as changes in the chemistry of oceans and atmosphere dramatically increased Earth’s mineral diversity to the almost 5000 species known today.

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