Time and process in sedimentary rocks at the dawn of animal life

Abstract

One of the most profound changes in the history of our planet was the relatively recent emergence of complex life—macroscopic, multicellular organisms with tissues. Sedimentary rocks record this evolutionary event, alongside other shifts in environment and climate, in fragmentary form. Sedimentological studies track change in space and relative time, and radiometric studies allow us to tie events to absolute time. Both are necessary to understand how and if changes in environment are linked to early animal evolution. This thesis combines both. Chapters 1 and 2 of this thesis explore early records of life on Earth that predate, in whole or in part, animal life. In Chapter 1, the molecular record of life's origins are explored for evidence of environmental influence and adaptation. I argue that environmental heterogeneity has been a key driver in life's history since its beginning. In Chapter 2, the Precambrian to Cambrian carbonate rock record is assessed in a quantitative, high-resolution database of more than 40 km of carbonate stratigraphy. The sedimentological insights derived from this work provide an independent record of changes in ocean biogeochemistry before and during the rise of animals. Chapters 3, 4, and 5 focus on the sedimentary rock record of the Ediacaran Period (635-541 Ma). Chapter 3 describes new Re-Os age constraints on Earth's largest negative carbon isotope excursion, the Shuram excursion. Chapter 4 presents additional Re-Os age constraints on the Ediacaran succession of Oman to explore shifts in Earth’s surface environments during the rise of animals. These novel constraints suggest an expansion of shallow water marine environments in the late Ediacaran Periods, possibly concurrent with the expansion of animals from deep to shallow water environments. Chapter 5 investigates the detrital zircon record of an Ediacaran unit, the Rainstorm Formation, and analyzes the role of grain size and sediment transport processes in generating bias in detrital mineral provenance records.Ph.D