Evidence of that calamitous day can be found in the Chicxulub crater, a heavily eroded 90-mile wide impact site located on Mexico's Yucatán Peninsula, which is widely believed to be the impact site for whatever triggered the mass extinction event.

In other words, "cometary shrapnel" from a long-period comet which pinged around our solar system could have caused the impact that led to a mass extinction, rather than an astroid.

In the paper, the researchers put forth their new calculations that increase by a factor of 10 the likelihood of long-period comets — meaning those which have orbital periods longer than 200 years — striking Earth.

The timing of these calculations would be "consistent with the age of the Chicxulub impact crater," the researchers explained, providing a "satisfactory explanation for the origin of the impactor.".

"What I ended up finding most striking was that a significant fraction of Earth-crossing comet —  Earth-crossing meaning comets 1 AU [astronomical unit] of the sun — were directly preceded by remarkably close encounters with the Sun," Siraj said.

A common theory on the origin of the Chicxulub crater suggests that the source originated from the main belt, an area between the orbit of Jupiter and Mars populated with asteroids.

Previously, evidence from the Chicxulub crater suggested the impact object was made of carbonaceous chondrite.

Yet we know from one successful sample-return comet mission that comets do contain carbonaceous chondrite, Siraj said.

Two geoscientists advanced the theory in 2013, partially because the levels of iridium and osmium around the impact site were lower than should appear in an asteroid and more apt for a comet impact. Siraj said studying iridium will be an "important active area of research" to better understand what impactor that caused the Chicxulub crater.