WHEN WORLDS QUAKE

The molten mystery beneath our feet.

The deepest human-made hole on Earth, drilled by the Soviets during the Cold War near the border between Russia and Norway, reaches more than 12 kilometers deep into the darkness of the Earth’s crust. Impressive, but barely a dent in the 6,000 kilometers that stretch to the center of the planet. Going further isn’t an option; the way is blocked by a boiling metal ocean. That’s why Tkalčić, a geophysicist at the Australian National University, considers seismology his “life’s calling”: The best tools scientists have for probing that inaccessible interior are earthquakes. And there are more of them than you’d think. In 2020 alone, seismographs recorded some 350,000 earthquakes around the globe. Most don’t rise to the level of human perception, but seismologists use them to image the Earth’s innards the same way radiologists use ultrasounds or X-rays to peer inside the body. Tkalčić explains these methods in rich but accessible detail. We learn, for instance, how plate tectonics regulate the climate by drawing down carbon deposits from the ocean floor, spewing it back into the atmosphere through volcanic eruptions. Meanwhile, the convection of liquid iron in the core produces the Earth’s magnetic field, which deflects solar wind and radiation. Without these dynamics, “life on Earth would not be possible.” Our planet, in Tkalčić’s rendering, is hardly an inert rock, but a restless network of roiling activity, with secrets still lurking in its depths. As the author traces the historical efforts to uncover those secrets, his narrative, at times, is overly expositional (“Charles Richter looked up at the starry sky of southern California and thought what a great job he had done in introducing the concept of magnitude into seismology, from astronomy”); nevertheless, the science is fascinating, and Tkalčić’s descriptions of his own fieldwork are riveting reminders of just how hard won the everyday facts of science really are. The author’s decades of research inform every page, and his enthusiasm for his subject is contagious.

A passionate scientific account of the alien world inside our home planet.