Dinosaur Extinction and Its Impact on New York's Geology

New York City’s evolution from a landlocked interior to a coastal powerhouse began with volcanic upheaval and one of Earth’s greatest mass extinctions. Tracing its geology over hundreds of millions of years reveals how ancient lava flows and shifting continents sculpted the harbor we know today.

The Geological Origins of New York City

To understand the deep-time drama behind New York’s famous harbor, we travel back roughly 450 million years. At that time, the region lay far from any ocean, embedded in the heart of an immense landmass that would later fracture into multiple supercontinents. Without a seaport, what is now New York City was surrounded by sedimentary plains and shallow rivers, rather than waves lapping at Manhattan’s shores. This early configuration set the stage for dramatic changes during the breakup of Pangaea some 200 million years ago.

The Footprint That Tells a Story

Fast-forward about 250 million years from New York’s landlocked phase, when paleontologist Paul Olsen uncovered a striking clue in a New Jersey quarry, 25 miles northeast of Manhattan. He found a three-dimensional impression of a giant crocodile relative in ancient mud—Postasucus—whose four-toed foot and handprints remain perfectly preserved. These fossilized tracks date to the late Triassic, around 230 million years ago, offering a snapshot of a world soon beset by catastrophe.

“Whatever caused the mass extinction must have been a catastrophic event,” Paul Olsen noted as he examined the disappearance of Postasucus footprints.

Paleontologists know that roughly half of all land animals vanished around the same time that these footprints ceased, marking one of the largest extinction episodes in Earth’s history.

Clues of a Catastrophic Event

Olsen suspected that the mass extinction and New York’s coastal emergence were linked. The ancient land under New York sat atop a zone of tectonic weakness—the plate boundary where continental fragments once converged to form Pangaea. Such boundaries are prone to earthquakes and volcanic activity. Directly above the fossil layer in the New Jersey quarry, Olsen observed a band of dark, fine-grained rock identified as basalt. Basalt forms when lava cools at the surface, suggesting a volcanic outburst coincided with the disappearance of Postasucus and other Triassic fauna.

However, the basalt layer at the quarry measured only a few feet thick, hardly the scale expected from truly global lava flows. To support his hypothesis that massive eruptions triggered the extinction and pried Pangaea apart, Olsen needed more compelling evidence.

The Search for Corroborative Evidence

That evidence emerged just across the Hudson River in the majestic Palisades cliffs. Geologist Matt Goring studied this dramatic sheet of basaltic rock—nearly 1,000 feet thick and stretching about 40 miles along the riverbank. The Palisades represent a vast flood of lava that once poured from fissures in the Earth’s crust, blanketing ancient North America in a deep layer of volcanic rock. Columnar jointing, the vertical, hexagonal columns carved by cooling lava, provided a visual testament to the scale of these eruptions, dwarfing the thin basalt at the New Jersey quarry.

Unraveling the Magnetic Secrets of Basalt

Though the Palisades’ immense size was persuasive, geologists had long debated whether this volcanic sheet connected to similar outcrops across the Atlantic. The key arrived in the 1950s with paleomagnetism, a technique that decodes the magnetic signatures locked into volcanic crystals as they solidify. Each basalt flow carries a record of Earth’s magnetic field orientation at the moment of cooling.

Goring’s team bored into the Palisades rock, extracting core samples and measuring the alignment of magnetic minerals. By comparing these readings to magnetic north, they calculated the original latitude where the basalt formed. Strikingly, the Palisades and corresponding basalt cliffs in Morocco shared not only the same age—around 200 million years—but the same paleolatitude. This provided definitive proof that New York and northwest Africa were once adjacent before the Atlantic Ocean opened.

The Transformation of a Continent

Around 200 million years ago, as Pangaea began to fracture, colossal volcanic eruptions rained lava across what is now Europe into Brazil and across the eastern margin of North America. The scorching eruptions sent fountains of lava high into the atmosphere, releasing vast volumes of greenhouse gases and triggering global warming. Temperatures soared, and half of all plant and animal species perished in the ensuing mass extinction, sealing the fate of Postasucus and many other Triassic organisms.

Meanwhile, the tidal forces and tectonic stresses that followed the volcanic pulse gradually widened the rifts. A new ocean basin formed between separating continents—the Atlantic Ocean—and New York’s ancient interior transformed into the coastal region that would foster its deep-water harbor. The city’s dramatic metamorphosis from landlocked terrain to seaside hub underscores the powerful interplay between mass extinction events and shifting geology.

Conclusion: The Lasting Impact of Geology

Our exploration of New York’s ancient past links dinosaur-era extinction to the volcanic forces that shaped today’s eastern seaboard. From a modest muddy footprint to towering basalt cliffs, the evidence reveals how tectonics, volcanism, and global cataclysms forged the landscape beneath modern Manhattan.

• Bold takeaway: Explore local stone outcrops or museum collections in your area to uncover the geological history beneath your feet and connect with Earth’s deep-time story.