There’s a giant hole in a small town in New Jersey. At the bottom of that hole, in a green, soupy sand, is a door to a world ruled by reptiles.
It was the end of the age of dinosaurs, and the corner of North America now called Mantua Township, New Jersey was ten miles offshore, under the Atlantic ocean. Mosasaurs dominated the sea, and sharks, rays, ammonites, turtles and fish swam through their shadows. The green sand was alive with clams, snails, crustaceans, and a whole menu of animals that would look at home on any seafood platter today – except that every species found here is long extinct.
While some of the creatures of the green sand have very close living relatives, like the moon snails and oysters, others aren’t quite like anything alive today, like the ammonites and mosasaurs. Sixty-five million years ago, a huge space rock hit our planet, and triggered a global mass extinction that wiped out dinosaurs, mosasaurs, ammonites, and many other forms of life that our tiny planet will never see again.
The thin layer of green sand found here, in a humble quarry in New Jersey, is from – roughly – the time of that extinction. It’s known as the “K/Pg boundary”, named after the two eras it draws a line between: the older Cretaceous and the newer Paleogene. We don’t know yet if the organisms here died in that disaster, because “roughly” for a paleontologist means “give or take a million years.” We may never know. The fossils here could have accumulated slowly over time, or after a flood or tsunami that happened a thousand years before the meteor hit. Ironically, it could have been a completely unrelated disaster that happened, by coincidence, the day before. Anything’s possible – and scientists at Drexel University and other institutions are working hard to narrow down those possibilities.
Three centuries of study
The history of research on the Hornerstown formation dates all the way back to the 1800s – almost to the very beginning of the field of paleontology itself.
Most of the fossils found at the Inversand quarry come from the Hornerstown formation, which dates to the end of the Cretaceous and beginning of the Paleocene, about 65 million years ago. The green sand of the Hornerstown formation is actually a glauconite marl, and has been mined by the Inversand company for decades as a water purifying substance. The layer just below it is called the Navasink formation. A few of the organisms listed on this website have been found in the Navasink formation, and date to the late Cretaceous.
The quarry in photos
More information about the Inversand quarry and the Hornerstown formation on other websites