The Earth is about 4.5 billion years old. How can we begin to grasp what this vast period of time really means, given that it is so far beyond the time scale of a human life, indeed of human civilization? Richard Fortey has devoted his long and prolific research career at the Natural History Museum in London to the study of fossils, especially the long-extinct marine arthropods called trilobites. In an earlier episode of Geology Bites, he talked about measuring time with trilobites. In this episode, he describes how it was the fossils in the geological record that gave us the first markers along the runway of deep time, providing the structure and language within which our modern conception of deep time emerged.

The Himalaya are just one, albeit the longest and highest, of several mountain ranges between India and Central Asia. By world standards, these are massive ranges with some of the highest peaks on the planet. The Karakoram boasts four of the world’s fourteen 8,000-meter peaks, and the Hindu Kush, the Pamir, the Kunlun Shan, and the Tien Shan each have many peaks above 7,000 meters. No mountain ranges outside this region have such high mountains. Yet we seldom hear much about these ranges.

In the podcast, Mike Searle describes the origin and geology of six central Asian ranges and how they relate to the Himalaya and the collision of India with Asia. India continues to plow into Asia to this day. How is this movement accommodated? Searle explains the extrusion and crustal shortening models that have been proposed and describes the detailed mapping he and his colleagues conducted in the field in northern India that showed that both mechanisms are operating.

Searle is Emeritus Professor of Earth Sciences at the University of Oxford.

The Caledonian orogeny is one of the most recent extinct mountain-building events. It took place in several phases during the three-way collision of continental blocks called Laurentia, Baltica, and Avalonia during the early stages of the assembly of the supercontinent Pangea. In the process, Himalayan-scale mountains were formed. While these mountains have been worn down today, we still see plenty of evidence for their existence in locations straddling the Atlantic and the Norwegian Sea. In the podcast, Rob Strachan describes the tectonic movements that led to the orogen and explains how we can reconstruct the sequence of events that occurred and what we can learn about today’s mountain-forming processes by studying the exhumed rocks of ancient orogens.

Strachan has studied the rocks of the Caledonian orogen for over 40 years, focusing on unraveling the history of the orogen in what is Scotland today. He is Emeritus Professor of Geology at the University of Portsmouth.