Geology Bites

We have known for decades that the Moon once generated a strong magnetic field — comparable in strength to Earth's — throughout the period from about 4.25 to 3.5 billion years ago. Only in the past few years have we learned that the field didn't simply switch off then: it weakened dramatically but lingered on, faintly, until as recently as 1.5 billion years ago, before disappearing entirely. As Sonia Tikoo explains in the podcast, we don't really understand either how the early field grew so strong or how any field could last so long — and no single mechanism seems able to account for both the intense early epoch and the long, weak tail that followed.
Sonia Tikoo studies the history of magnetic fields on the Moon and other small solar system bodies using paleomagnetism and fundamental rock magnetism.  She is an Assistant Professor in the Department of Geophysics at Stanford University.

Birds are the only dinosaurs that survived the asteroid impact 66 million years ago — but not all birds did. In this episode, Steve Brusatte draws on the fossil record to explain which birds came through the extinction, and what set the survivors apart from the many that perished alongside the rest of the dinosaurs. He traces the evolutionary transition from ground-living theropods to modern birds, drawing on the spectacular feathered fossils unearthed over the past three decades in northeastern China.
Brusatte is Professor of Palaeontology and Evolution at the University of Edinburgh and author of The Story of Birds, published this year.

A key development in the history of the early Earth is the formation of lithospheric plates that move independently of one another. In this episode, Brenner describes how he used paleomagnetic methods to detect relative motion between two ancient cratons, the East Pilbara and the Kaapvaal, 3.5 billion years ago. This is a full billion years earlier than any previous such detection, and it enables us to narrow down the kind of tectonics operating in the Paleoarchean. Of the candidate regimes, episodic subduction models fit his data best.
Brenner is a Postdoctoral Associate in the Department of Earth & Planetary Science at Yale University.

Most of the material in the Earth and other planets exists under extremes of pressure and temperature quite unlike those we inhabit on the surface of the Earth. Steve Jacobsen is a mineral physicist who studies how rocks and minerals behave under such alien conditions. In the podcast, we discuss his experiments and what we’ve learned about three extreme environments: the core-mantle boundary, the mantle transition zone, and the surface of the Moon.
Jacobsen is a Professor of Geological Sciences at the University of Colorado Boulder. The image shows him in his optical spectroscopy lab, where extreme conditions found throughout the solar system are re-created.

Though turbidity currents are massive and frequent underwater events, we have rarely observed them directly. Esther Sumner is one of the few researchers who has. In the podcast, she describes what it's like to instrument an active submarine canyon, what these flows have revealed about the way sediment moves across the seafloor — and the day her team accidentally flew an underwater robot into a live turbidity current in the Mendocino canyon off the coast of California. She is an Associate Professor of geology and geophysics at the University of Southampton.