Rocks as Storytellers: How Geology Deeply Shapes New York's Skyline and Earth's History

Geologist Anjana Khatwa explains why New York's skyline clusters around bedrock, notably the Manhattan schist, and how rocks carry Earth’s history. The conversation covers zircon dating that unlocks ages as old as 4.4 billion years and how plate tectonics rewrote our planet, from the birth of continents to the formation of oceans. It also ties geology to human culture, from the chalk belt in the southern United States linked to cotton plantations to indigenous stories that frame geological processes. The episode frames rocks as foundational to life, energy, and climate challenges, urging a careful approach to mineral extraction and resource use as we move forward.

Introduction: What rocks tell us about our world

In this Shortwave episode, Anjana Khatwa, a geologist and author, illuminates how the landscape beneath a city is not a mute backdrop but a living archive. She explains that New York’s skyline sits atop clusters of bedrock, especially the hard Manhattan schist, which roots the city’s tallest buildings. The conversation emphasizes that rocks are not inert; they carry long histories that shape our energy systems, climate futures, and cultural memories.

Rocks as storytellers and the deep past

Khatwa argues that rocks are ancient storykeepers of Earth’s evolution and, at the same time, memory keepers of human encounters with them. She emphasizes that geology links everyday life to planetary history, from the fuel that powers modern society to the coffee we drink, which can be affected by volcanic soils and mineral content. The book The Whispers of Rocks bridges scientific narrative with Indigenous knowledge to illustrate how geology underpins human experience and culture.

“rocks are ancient storykeepers of how our earth evolved” and “rocks contain stories, and those stories explain our world” are two recurring ideas she frames to connect deep time with contemporary life.

Dating the Earth: zircon as a clock

The discussion then turns to zircon, a mineral that records the moment a rock formed. A Lewisian gneiss sample dating back to 2.7 billion years old contains zircon crystals that reveal age when radioactive decay is measured. Zircon dating has pushed scientists toward a maximum Earth age of about 4.4 billion years, aligning with estimates of Earth’s formation. This method helps reconstruct environments from a molten adolescence of the planet, when water was scarce and life had yet to appear.

Plate tectonics: from war to a unifying theory

The hosts recap how the theory of plate tectonics gained acceptance in the mid-20th century, aided by the mapping of the Atlantic Ocean floor. Marie Tharp and Bruce Heezen’s work revealed the mid-Atlantic ridge and paleomagnetic reversals, providing the mechanism by which continents drift and oceans open and close. The idea that continents ride on buoyant plates and interact at boundaries explains the geography of New York and the world—where mountains rise and erode, and bedrock becomes the anchor for cities and cultures.

Geology shaping society: chalk, soil, and history

The conversation then moves to chalk, an organic rock formed from oceanic microorganisms that settled into sleeping white layers. Weathering chalk formed the Black Belt soils of the American South, a region whose agricultural history—cotton plantations and enslaved labor—left lasting demographic patterns and political leanings. The example shows how geology can influence social and political geography across centuries.

Indigenous knowledge and the living Earth

The episode also weaves Indigenous storytelling with scientific understanding, such as Cherokee narratives about the great buzzard shaping valleys and mountains. These narratives complement scientific models, illustrating that geology intersects with culture in meaningful ways and that rock stories can illuminate both past and present human experiences.

Why this matters for the present and future

Geology provides a framework for understanding climate change, mineral consumption, and how humans interact with Earth. Rocks are stable yet vulnerable to extraction and alteration, and their stories risk loss if transformed or removed without care. The episode closes with a call to view rocks as foundational to human life—physically, culturally, and economically—and to consider the long-term consequences of resource use in a changing world.