Roughly four billion years ago, during the Hadean and early Archean, Earth's crust was a patchwork of newly stabilized blocks whose tectonic behavior remains debated among geochemists. Recorded live at Goldschmidt 2026 in Montréal, this episode asks whether plate tectonics began as one clean global shift or emerged unevenly across different regions and times. Ola and Amara compare zircon evidence from the Acasta Gneiss Complex and Saglek Block, review GEOTRACES isotope tracers used to reconstruct ancient seawater chemistry tied to snowball Earth and the Great Oxidation Event, and debate a new molybdenum-isotope zircon method against ocean tracers and noble gases as candidates for a deeper future episode. Listeners curious about early Earth geochemistry and how scientists test competing tectonic models will find a clear picture of where the evidence currently stands.

Amara opens with a cinematic tour of the 520-million-year-old Xiannüdong reef in Shaanxi, China, where hot Cambrian seas hosted nearly every major animal group — except one conspicuously absent group of filter-feeders.

In this episode, we cover Scene-setting / cold open, Background / mystery setup, Core science / the discovery, and more.

Three hundred and nine million years ago, the land beneath modern Chicago was a swampy equatorial delta — oxygen at 35%, club mosses thirty meters tall, and dragonflies the size of hawks. The central question of this episode: did early four-legged vertebrates develop through amphibian-style metamorphosis, or did they hatch as miniature adults from the start? Ola and Amara examine the Pardo and Mann 2026 Science paper, which presents hatchling embolomere fossils from Mazon Creek with fully forming limbs and no external gills, then work through the fin-to-limb timeline from Tiktaalik to Romer's Gap, and debate whether Carboniferous animals can legitimately inform models of Devonian development. Listeners will come away understanding why modern amphibian metamorphosis may be an evolutionary novelty rather than the ancestral vertebrate condition.

Sixty-six million years ago, in the Late Cretaceous, foraminifera-filled oceans teemed beneath skies that had never seen a mass extinction — until a 10-kilometer asteroid ended that world in seconds. This episode of Fault Lines asks whether the Chicxulub impact was purely a catastrophe, or whether it also structured what came next.

Ola and Amara examine a June 2026 study in Communications Earth and Environment finding the Chicxulub crater sustained a hydrothermal system for at least 8 million years, a January 2026 study in Geology documenting new plankton species appearing fewer than 2,000 years post-impact, and what both findings could mean for detecting life around impact craters on Mars. Listeners interested in deep time, evolutionary biology, or astrobiology will come away with a clearer picture of how destruction and recovery can be simultaneous rather than sequential.

On June 15, 1991, the sky over Central Luzon turned white as Mount Pinatubo sent an ash column 40 kilometres into the stratosphere. The central question this episode tackles is whether the canonical 0.5 degrees Celsius of global cooling attributed to Pinatubo is actually reliable — and what is at stake if it is not. Ola and Amara trace the mechanism of stratospheric aerosol forcing from Pinatubo's 22-day global circumnavigation to the contested Toba supervolcano eruption of approximately 74,000 years ago, then scale further back to the Siberian Traps and Deccan Traps of the Permian and Cretaceous periods, roughly 252 and 66 million years ago respectively. They close on the termination shock problem in geoengineering research. Listeners interested in climate science, deep-time geology, or the governance of solar radiation management will come away with a clearer sense of how much certainty — and how much uncertainty — rests on a single volcanic event.

Seven hundred and seventeen million years ago, the equator was buried under sheets of ice in what geologists call the Sturtian glaciation, a freeze that lasted 56 million years. This episode asks a single question: was Snowball Earth a static, locked prison, or something far more dynamic?

Ola and Amara examine two competing answers from the Cryogenian period (approximately 717 to 660 million years ago). The Southampton team's analysis of 2,600 varve layers from Scotland's Garvellach Islands reveals seasonal and solar cycles preserved inside Snowball rock, while Harvard's PNAS model proposes repeated freeze-thaw cycles driven by CO2 feedbacks tied to the Franklin Large Igneous Province. The episode also covers what either scenario means for the survival of aerobic animal ancestors across one of Earth's most extreme climate intervals.

Listeners interested in deep-time climate science, Precambrian geology, or the origins of complex life will come away with a clear understanding of what the rock record does and does not yet confirm.

Sixty-six million years ago, Earth was a greenhouse world with no polar ice, CO2 above 800 ppm, and palm trees growing in Alaska. This episode of Fault Lines asks why all that warmth slowly disappeared over the following 50 million years of the Cenozoic era. Ola and Amara examine a University of Southampton PNAS study finding that seawater calcium dropped by more than half across that period, walking through the foram proxy method used to reconstruct the record, debating whether calcium decline drove CO2 down or simply tracked alongside it, and weighing the Drake Passage and Antarctic Circumpolar Current as competing explanations. Listeners interested in deep-time climate science will come away understanding why geochemical ocean processes, not just tectonics or ice dynamics, may be the true long-run thermostat of Earth's climate.

On May 18, 1980, a magnitude-5.1 earthquake stripped the entire north face of Mount St. Helens in seconds, releasing the largest debris avalanche in recorded history. The episode asks whether the monitoring revolution that followed actually prepares us for the volcanic events capable of ending mass life on Earth. Ola and Amara move from the 4.2 cubic kilometers ejected at St. Helens up to the Siberian Traps' four million cubic kilometers of lava — the Large Igneous Province tied to the Permian-Triassic extinction event 252 million years ago — then work through the gas chemistry cascade and sill-emplacement mechanism that made the eruption so lethal. They close by stress-testing modern monitoring tools against a threat that has no cone, no point source, and no seismic spike to detect. Listeners will come away with a clearer sense of where volcanology's hard limits actually are.

Two hundred and fifty-two million years ago, a biologically stable marine world built over fifty million years was erased in geological near-silence. This episode of Fault Lines examines the central question of the Permian-Triassic extinction: what actually killed 96% of marine species, and did anything that followed deserve to be called recovery? Ola and Amara walk through the Siberian Traps as the volcanic trigger, the cascading kill chain of thermal spikes, ocean anoxia, and acidification, and a January 2026 study in npj Biodiversity showing that Early Triassic ecosystems rebounded rapidly but remained structurally unstable. Listeners will come away understanding the critical difference between taxonomic recovery, measured in millions of years, and true ecological recovery, which may have taken fifty million years or more.