Last Minute Lecture

Seismic Layering, Gravity Anomalies, and the Magnetic Field — Probing Earth’s Interior | Interlude D from Earth: Portrait of a Planet How do geologists know what’s inside the Earth? In Interlude D of Earth: Portrait of a Planet , Stephen Marshak reveals the geophysical detective work that has unraveled our planet’s internal structure—using seismic waves, gravity measurements, and the mysteries of Earth’s magnetic field. To see a visual breakdown, watch the chapter video on YouTube , or keep reading for a comprehensive summary of how we peer into Earth’s hidden depths. Seismic Waves: Earth’s X-Rays Reflection & Refraction: Seismic (P- and S-) waves bend and bounce as they pass through materials with different properties, revealing Earth’s internal layers. Key Boundaries: The Moho marks the crust-mantle boundary. The low-velocity zone (LVZ) beneath the oceanic crust is linked to the ductile asthenosphere. Seismic shadow zones reveal the existence of the liquid oute...

Earthquakes Explained — Causes, Seismic Waves, Hazards, and Prediction | Chapter 10 from Earth: Portrait of a Planet Why do earthquakes strike without warning, and how do scientists measure and predict these violent pulses of the Earth? In Chapter 10 of Earth: Portrait of a Planet by Stephen Marshak, we journey into the heart of seismic science—discovering how earthquakes occur, what hazards they cause, and how societies can prepare. For a full podcast summary, watch the YouTube chapter video or explore the detailed written breakdown below. How and Why Do Earthquakes Occur? Earthquakes are sudden releases of energy caused by the stick-slip motion along faults, when built-up stress finally overcomes friction. This process is known as the elastic rebound theory . The initial rupture point is called the hypocenter , while the location directly above it at the surface is the epicenter . Earthquakes can be preceded by foreshocks and followed by aftershocks . Types of Faults a...