Sedimentology of Precambrian Depositional Systems: Understanding the Earth's Surface in Deep Time

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Most people tend to view the natural world as constant. A storm may blow a tree down or a bluff may be slowly eaten away by the waves, but the oceans and the mountains are viewed as forever. When people think of forever in this way, they are approaching the concept from a human point of view, limited by our short lifespans. However, the oceans and mountains also have lifespans and these are much longer. Only twenty thousand years ago most of Canada was covered by ice. Everything we see today was either not here or, if it was large and solid, was all or mostly under the ice. The further back in time we go, the greater the difference from the present. Two thousand seven hundred million years ago the central area of Canada consisted of volcanic islands similar to the Caribbean region; North America did not exist; a world ocean dominated the planet; the most advanced life was bacteria; and the atmosphere had no oxygen. We know this because the rocks that were formed at this time from volcanic eruptions, and the sedimentary rocks produced by the erosion of the islands, occur as bedrock under large areas of central Canada. My research uses clues left behind in sedimentary rocks to discover what the geography looked like and what sedimentary processes were operating, when the Earth was a young planet. I am particularly interested in the composition of the atmosphere and ocean during the time period 3.0 to 1.4 thousand million years ago. In approximately the middle of this time period photosynthesizing organisms added significant amounts of oxygen to the atmosphere and oceans. I analyse minerals in sedimentary rocks that formed from chemicals precipitated in the ocean during this time period. These minerals grew on the bottom of the ocean and are now contained in sedimentary rocks. The composition of the minerals provides me with the information I need to form conclusions on how the chemistry of the ocean-atmosphere system developed through time. The importance of this work is not limited to understanding how the oceans and atmosphere were transformed over time. The chemistry of the surface of the Earth was a major control on the evolution of various forms of life on Earth. Understanding ocean-atmosphere chemistry is essential to unraveling life's early history.