Extinction of the Dinosaurs Timeline

Working as a geophysicist in 1978, Glen Penfield identified geophysical evidence of a massive buried impact crater on the Yucatán Peninsula. The structure was later recognized as the Chicxulub crater, the impact site linked to the Cretaceous–Paleogene extinction event.

Image source: Chicxulub crater

In 1980, Nobel Prize-winning physicist Luis Alvarez, his son geologist Walter Alvarez, and chemists Frank Asaro and Helen Michel discovered that sedimentary layers worldwide at the Cretaceous–Paleogene boundary contain iridium concentrations many times greater than normal (30, 160, and 20 times in three sections originally studied), supporting an asteroid impact hypothesis.

Image source: Cretaceous–Paleogene extinction event

Identified in 1990 based on Glen Penfield's 1978 work, the Chicxulub crater is oval with an average diameter of roughly 180 km (110 mi), about the size calculated by the Alvarez team, confirming the impact site of the asteroid that caused the mass extinction.

In 2007, it was proposed that the impactor belonged to the Baptistina family of asteroids, suggesting a shattered parent body in the asteroid belt supplied the object that struck Earth at the end of the Cretaceous.

Image source: Baptistina family

It was reported in 2009 that the asteroid 298 Baptistina does not share the chemical signature of the K–Pg impactor, weakening the proposed link between the Baptistina family and the extinction-causing asteroid.

In March 2010, an international panel of 41 scientists reviewed 20 years of scientific literature and endorsed the asteroid hypothesis, specifically the Chicxulub impact, as the cause of the extinction, ruling out other theories such as massive volcanism.

A 2011 Wide-field Infrared Survey Explorer (WISE) study of reflected light from the asteroids of the Baptistina family estimated their break-up at 80 million years ago, giving them insufficient time to shift orbits and impact Earth by 66 million years ago.

Image source: Wide-field Infrared Survey Explorer

In 2016, a scientific drilling project obtained deep rock-core samples from the peak ring around the Chicxulub impact crater, providing new insight into the formation and consequences of the impact.

A 2016 drilling project into the Chicxulub peak ring confirmed that it contained granite ejected within minutes from deep in the Earth, and that it contained hardly any gypsum, the usual sulfate-containing sea floor rock in the region — a finding with major implications for the severity of post-impact climate cooling.

In 1988, researchers replied to claims about dinosaur decline by arguing that paleontologists were being misled by sparse data, defending the interpretation of patterns in the fossil record leading up to the extinction event.