AUSTIN, Texas (ABC4) – What killed the dinosaurs? It’s a million of years old mystery scientists have been trying to solve. Now, researchers think they have finally closed the case.

Evidence discovered in the 1980s in a rock layer caused many scientists to believe since the 1980s, an asteroid caused the extinction event.

Others believed it was from volcanic activity.

The apocalyptic idea of a global winter caused by the impact of a meteor or the eruption of volcanoes killing the giant reptiles became romanticized in people’s imaginations. But scientists were having problems finding the “smoking gun.”

How was the mystery solved?

According to a release from the University of Texas, a discovery helped in the search. During the 1990s, the Chicxulub impact crater was discovered beneath the Gulf of Mexico and was “the same age as the rock layer.”

An asteroid slammed into planet earth 66 million years ago and hit the Yucatan Peninsula, where there is a crater half on land and half under the water.

Now, the new study essentially seals the dinosaur’s fate, according to researchers, “by finding asteroid dust with a matching chemical fingerprint within that crater at the precise geological location that marks the time of the extinction.”

It was death by an asteroid.

The crater left by the asteroid that wiped out the dinosaurs is located in the Yucatán Peninsula. It is called Chicxulub after a nearby town. Part of the crater is offshore and part of it is on land. The crater is buried beneath many layers of rock and sediment. A 2016 mission led by the International Ocean Discovery Program extracted rock cores from the offshore portion of the crater. Credit: The University of Texas at Austin/Jackson School of Geosciences/ Google Map.

“The circle is now finally complete,” says Steven Goderis, a geochemistry professor at the Vrije Universiteit Brussel, who led the study published in Science Advances on Feb. 24.

According to the release from U.T., “The new information is the latest from a study 2016 International Ocean Discovery Program mission co-led by The University of Texas at Austin that collected nearly 3,000 feet of rock core from the crater buried under the seafloor. Research from this mission has helped fill in gaps about the impactthe aftermath, and the recovery of life.”

So what was the critical clue?

It’s Iridium. The metal element is rare on earth, but present in elevated levels in certain asteroids. An iridium spike in a geologic layer found worldwide is what led investigators to the asteroid hypothesis. In the new study, the spike of the element is found in the crater itself and has been dated to 2 decades within the impact.

ABC4 asked Randy Irmis, Chief Curator and Curator of Paleontology, Associate Professor Geology and Geophysics, University of Utah, if Utah had the Iridium spike?

He said, “We have sedimentary rocks called the North Horn Formation that is from the time of the Chicxulub impact, so they should contain a layer with an iridium spike, but we haven’t found it yet in this geologic formation.  The iridium layer spike has been found in neighboring states such as New Mexico, Colorado, and Wyoming.”

“We are now at the level of coincidence that geologically doesn’t happen without causation,” said co-author Sean Gulick, a research professor at the UT Jackson School of Geosciences who co-led the 2016 expedition with Joanna Morgan of Imperial College London. “It puts to bed any doubts that the iridium anomaly [in the geologic layer] is not related to the Chicxulub crater.”

To get an idea of this asteroid’s size, it was seven miles wide and wiped out 75% of life on Earth, which includes what is called non-avian dinosaurs.

Utah’s Irmis says, “We already knew that non-flying dinosaurs went extinct at the end of the Cretaceous Period and at the same time as the Chicxulub impact (and iridium spike), and so we already knew the dinosaurs (including Utah’s only Tyrannosaurus rex) form the North Horn Formation were some of the last non-flying dinosaurs. But if we could find the iridium spike, it would help us pinpoint the extinction-level in Utah.”

Researchers now estimate the dust kicked up by the impact circulated in our atmosphere for no more than a couple of decades, which basically is how long it took for everything to starve to death. Now researchers can put a time on the extinction.

“If you’re actually going to put a clock on extinction 66 million years ago, you could easily make an argument that it all happened within a couple of decades, which is basically how long it takes for everything to starve to death,”

Will knowing when the extinction happened and what layer to look for help Utah’s Paleontologists find more fossils?

Irmis said, “Not specifically – fossils are found in all different age sedimentary rocks.  But the iridium spike is an excellent marker in time – it tells us where the end-Cretaceous extinction occurred and where the boundary is between the Cretaceous and Paleogene periods.  So if we know where the iridium spike is, we know we should only find dinosaurs (and other Cretaceous fossils) below that level.”