If we go back in time twelve thousand years from the present, to a period marking the formation of the Puget Sound within the Pacific Northwest (PNW) region of North America, we see geo-climatic conditions drastically different from those predominating on Earth today. With one half of Earth's surface covered in ice, extensive glaciation  drove massive landscape alteration and mass extinction of biota. This glaciation progressed via a feedback loop of changing abiotic forces,including drastic reductions of mean global temperature.