A Chesapeake Bay Prehistory Lesson

The rock formation at the North Carolina site showing impacts

 from the ancient tsunami, with lines superimposed to distinguish

 layers. The reddish layer includes plinthite, followed below by

 ash and crushed rock material.

 A couple of articles I've had sitting in tabs for a while: WHRO, Geologists uncover new evidence from ancient asteroid that hit the Chesapeake Bay

Almost a decade ago, retired consulting geologist Bob Ganis was investigating some fossils in Moore County, N.C. when he got a call from a local property owner nearby. 

A pipeline was set to be constructed through the edge of her property called Paint Hill Farm, and she wondered if Ganis might like to come investigate the temporary trench as part of his research. Ganis accepted the offer and it became “one of the most strange days of my life,” he said.

He took a look at the rock layers exposed about 10 feet deep and was “totally baffled.” What he saw didn’t align with his geological understanding of the region. “I had no idea what it was, and no reports of this kind of geology were available to understand what it was,” he said.

Thus began a yearslong quest to get to the bottom of the mystery trapped in sediment. The first piece of the puzzle was determining the age of the rock layers in question.

Ganis said he found fossilized shark teeth nearby and worked with peers who helped date them to the late Eocene era, which lasted from about 56 to 34 million years ago. Next Ganis connected with Ralph Willoughby with the South Carolina Geological Survey, and described the mysterious sediment layers. They methodically went through the rock beds to try and explain each within the geological context of the region. “When we get to the top, this explanation of all this rubble at the top, we're still scratching our heads,” Ganis said. “‘What is this stuff?’”

One day, looking at photos from the trench site, “a light bulb goes off,” he said. “It struck us (that) this is a tsunami deposit.” There was no geological history to explain why such a deposit would be there, except for one: the meteoroid strike up in Virginia on that fateful day 35 million years ago.

The asteroid, moving at about 44,000 miles per hour, was about 2 to 3 miles wide and blasted an enormous crater into the continental shelf of modern day Virginia, according to the U.S. Geological Survey.

Much of the crater is still underwater in the bay, which is why it took until recent decades for scientists to discover. The circular outline of the impact in Hampton Roads includes the bottom half of the Eastern Shore, northern edge of Norfolk and eastern outskirts of the Peninsula and Middle Peninsula.

Like any object that lands in water, the asteroid caused a big splash – a giant tsunami likely thousands of feet high, “the kind of tsunami that the world rarely sees,” Ganis said.It likely washed over the Blue Ridge Mountains and swept across the Southeast – maybe even over the Atlantic Ocean to lap at the shores of Africa and Europe, he said.

Scientists described such a wide-reaching tsunami when they first investigated the Chesapeake Bay impact crater but no one had found actual remains of it. Ganis’ team homed in on the tsunami as a likely explanation for the Paint Hill rock formation, but needed more evidence to prove it. The bottom layer featured charcoal, natural glass and other rock fragments; materials you would expect to fly out of the impact, Ganis said. It also had the hallmarks of a “tremendously hot blast.” Another layer contained ash from the explosion.

A modern Great White Shark tooth

Moving forward a few million years, to the Southern Maryland Chronic,  Calvert Fossils Reveal Shark Evolution

Fossil discoveries along Maryland’s Calvert Cliffs reveal that ancestors of the great white shark, dating back 15 million years, consumed marine mammals like dolphins and whales despite lacking the serrated teeth of modern great whites (Carcharodon carcharias), according to a study published on June 27, 2025. The findings, led by Dr. Stephen J. Godfrey, curator of paleontology at the Calvert Marine Museum, challenge previous assumptions about the diet of the Miocene Epoch shark Carcharodon hastalis.

A C. hastalis tooth I found recently

 

Modern great white sharks use boldly serrated, triangular teeth to slice energy-rich marine mammals, such as seals and dolphins, into bite-sized pieces. In contrast, Carcharodon hastalis, an ancestor from 15 million years ago, had comparably sized but unserrated teeth. Scientists long assumed this species primarily ate smaller prey, like fish, due to the lack of serrations. However, two fossilized vertebrae—one from a small dolphin and another likely from a small baleen whale—found along the fossil-rich Calvert Cliffs, contain embedded, unserrated teeth from Carcharodon hastalis. These fossils confirm that the sharks fed on marine mammals before serrated teeth evolved. The discoveries suggest that feeding on large prey with unserrated teeth may have driven the evolution of serrated cutting edges in later species. An intermediate species, Carcharodon hubbelli, now extinct, developed lightly serrated teeth, bridging the gap to the modern great white’s steak-knife-like dentition. The study, published in Acta Palaeontologica Polonica, involved researchers from St. Mary’s College of Maryland, Johns Hopkins University Materials Science and Engineering, and syGlass, which used virtual reality to visualize a 3D scan of one embedded tooth.

One fossilized vertebra was CT-scanned at Johns Hopkins University, revealing the precise positioning of the shark tooth within the bone. The 3D visualization, processed using syGlass’s virtual reality engine, provided detailed insights into the predation event. These analyses confirmed the teeth’s pointed crowns penetrated the vertebrae, indicating active predation or scavenging by Carcharodon hastalis on marine mammals.

C. hastalis teeth are among the best treasures from the beach, not as rare as Megalodon, for sure, but rare enough that finding one makes it a pretty good day on the beach. The Miocene seas would have have been pretty terrifying, between Megalodon, the more common hastalis,and the ancestor of todays Tiger Shark, not to mention some seriously toothed whales, including  Squalodon and Livyatan.