Researchers are taking part in a groundbreaking effort to drill offshore into the very heart of the impact crater of the asteroid that killed the dinosaurs, and at a depth of around 700 meters (2,300 feet), they have just made their first breakthrough.

The demise of the non-avian dinosaurs was somewhat of a mystery until only 38 years ago. Many causes for the mass extinction event at the end of the Cretaceous period 66 million years ago had been suggested, but the discovery of a partly submerged, incredibly symmetrical arc off the coast of Mexico in 1978 was the first piece of a remarkable puzzle that culminated in a vision of the apocalypse.

This crater, 180 kilometers (110 miles) in diameter and 20 kilometers (12 miles) in depth, was created by an asteroid no more than 10 kilometers (6 miles) long. Now, scientists have their first sample from the crater.

Core on deck! first glimpses through the liner.

Image JLofi@ECORD_IODP.#exp364 pic.twitter.com/16Ir1YeJEf — Outreach (@ESO_Outreach) April 25, 2016

The international team working off the coast of the Yucatán Peninsula, sponsored by the International Ocean Discovery Program (IODP), has brought up rock samples from 670 meters (2,200 feet) beneath the seafloor. This rocky core contains pieces of the granite bedrock that were churned up upon impact, along with fluid-filled cracks originally deposited at extremely high temperatures when the impact occurred.

This core, the so-called “peak ring,” can ultimately be used to constrain estimates of how much energy the impact generated. Although there was a recent debate as to whether or not they had officially drilled into the peak ring, there is now almost no doubt.

“We are in the peak ring by about 80 meters (262 feet),” Joanna Morgan, one of the chief scientists on the expedition and a professor of geophysics at Imperial College London, told IFLScience. It’ll be awhile before any data interpretation is carried out, and for now, the task is to keep on drilling down into the depths. The team is funded to keep drilling until June 6, creating a hole 1.5 kilometers (0.9 miles) deep in the process.

An animation showing the impact crater. David Fuchs/University of Arizona/Wikimedia Commons; CC BY 3.0

The Chicxulub crater, as it became known, emerged as the energies of over 920 billion “Little Boy” Hiroshima atomic weapons were instantaneously unleashed, melting the landscape, creating continent-sized tsunamis, and burning ash that darkened the sky and froze the world. This impact event turned the rock it hit into a mushy, fast-moving fluid, and the core of the crater, as is often observed, was forced up into the sky. Sometimes this collapses into a single central mound, but in this case, multiple central peaks were generated.

Although scientists have previously excavated some of the crater remnants on land, some of the most revealing segments of it arguably lie underwater, and this project hopes to find them to constrain just how truly devastating the impact event was. By looking at the central peak ring, sometimes referred to as the “retarc” – that’s “crater” backwards, of course – estimates can be made as to just how much the asteroid liquefied and melted the crust.

Peak rings have been seen on impact craters all across the Solar System, from Mars to Mercury to the many moons of Saturn and Jupiter, but thanks to our active climate on Earth, peak rings – along with most of their original craters – are buried or eroded away over time. The Chicxulub peak ring appears to be relatively intact.

“Currently we are drilling impact breccia – the sequence that covers impact craters – and we expect to penetrate into the crater floor in about 50-80 meters (164-262 feet),” Morgan added, hinting that a second breakthrough is about to follow the all-but-confirmed first.

Raditladi crater, featuring a central peak ring, on Mercury. NASA