Throughline Winter is Coming
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Nov 6, 2025 
David Sepkoski, a historian of science and author, joins for an intriguing exploration of how the discovery of the dinosaur extinction event during the Cold War shifted our understanding of catastrophic risks. The discussion weaves through Walter Alvarez's groundbreaking research linking iridium to an asteroid impact. Sepkoski reveals how these insights paralleled nuclear winter models championed by Carl Sagan, ultimately influencing public perception and policy against nuclear war. The conversation highlights the intertwined fates of dinosaurs and humanity through the lens of scientific advocacy.
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Father's Rock Sparked A Big Idea
- Louis Alvarez, a Nobel-winning physicist, examined a thin KT boundary layer chunk his son Walter brought from Gubbio and felt a visceral reaction to its mystery.
- He applied physics tools to measure iridium and sparked the asteroid-extinction theory that explained the sudden dinosaur die-off.
A Father's Letter After Hiroshima
- Louis Alvarez volunteered on the observation plane over Hiroshima and later wrote a reflective letter to his young son Walter about the bomb's moral weight.
- That wartime experience shaped his belief that catastrophic weapons might force global change.
Iridium Fingerprint Linked To An Impact
- Louis used trace-element detection to find an iridium spike at the KT boundary that matched extraterrestrial sources.
- That chemical fingerprint provided a precise, global timestamp linking an impact to mass extinction.
