In recent years, the warm period — known as the Paleocene-Eocene Thermal Maximum (PETM) — has become a major point of interest for researchers as it’s perhaps the best past analog to today’s human-induced climate change.

Atmospheric carbon dioxide increased rapidly during this warming event, and an accompanying spike in global temperatures of about 5 to 8 degrees Celsius lasted for approximately 150,000 years.

This tells us that there was an extraterrestrial impact at the time this sediment was deposited,” Dr. Schaller said.

“The coincidence of an impact with a major climate change is nothing short of remarkable.”

The researchers spotted the spherules at the base of a layer of fine clay believed to mark the start of the PETM.

The samples came from drill cores taken in suburban Millville and Wilson Lake, NJ, and from a streambank in nearby Medford, NJ.

The 30-foot-thick section of fine material, known as the Marlboro clay, is found in several areas along the U.S. East Coast, and appears to have been laid down rapidly.

All the microtektites came from a 7- or 8-inch layer at its base.

A fourth sample, correlated to the same time, came from a deep-seabed core taken off Bermuda.The research is presented in a paper published online this week in the journal Science.