The day the dinos died

Drill core from Chicxulub Crater revealed first 24 hours after the asteroid impact

Much of the dinosaurs may have died 66 million years ago on the first day after the impact of the Chicxulub asteroid. © serpeblu / iStock
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Deadly day: Researchers first reconstructed what happened in the first 24 hours after the impact of the "Dinokiller" asteroid 66 million years ago. The data are provided by a drill core from the Chicxulub crater in Yucatan. He reveals that only a few minutes after the impact, the first tsunamis were triggered, and at the same time, the vegetation ignited thousands of miles away. That alone could have killed many dinosaurs and other animals.

About 66 million years ago, the impact of the Chicxulub asteroid in Yucatan triggered a global mass extinction - and the demise of the dinosaurs. The impact released the energy of ten million Hiroshima bombs in fractions of a second and could have destroyed all life in the far reaches in the first few hours and days. According to evidence, the impact triggered widespread fires, tsunamis, and a potentially prolonged period of severe climate cooling - an impact winter.

Gravity chart of the 66 million year old Chicxulub crater in Yucatan. © NASA

Drill core from the "Ground Zero"

But what happened immediately after the impact, only now reveals a core from the inner crater rim of Chicxulub crater. It was extracted in 2016 as part of the International Ocean Discovery Program (IODP) and analyzed by Sean Gulick of the University of Texas at Austin and his colleagues. "The drill core documents the events directly from Ground Zero, " says Gulick. "He tells us about the impact processes from the position of an eyewitness."

Already the first investigations reveal the catastrophic impact of the impact: On the first day after the impact alone more than 130 meters of material were deposited in the Chicxulub crater. "This accumulation is among the highest ever found in geology, " say the researchers. In addition to pieces of debris and sediment, these deposits also contain typical impact rock, including shocked quartz crystals and rock solidified into glass.

Billions of tons of vaporized rock

In the first moments of the impact, sediments and bedrock were thrown out in a huge explosion. Both the asteroid and a large part of the subsoil evaporated and were transported high up into the atmosphere. The core data now show that hardly any sulphurous subsoil remained in the crater: While the surrounding rock contains 30 to 50 percent sulfur-containing evaporites, the crater is only less than one percent, as the researchers report. display

Gulick and his team conclude that the Chicxulub impact has given far more than the previously estimated 325 billion tons of sulfur into the atmosphere. This enormous influx of cooling sulfur aerosols has caused a long-lasting impact winter with darkening of the sunlight. "Our findings support such a sulfate-aerosol-induced global cooling and reduction of photosynthesis as an important kill mechanism of this disaster, " say the researchers.

Heat and fire

But on the first day of the catastrophe, there was nothing to tell - on the contrary: the enormous heat of the impact, combined with the glowing particles, which spread over the earth's surface over thousands of miles, released a fiery inferno within hours. "The impact cloud alone generated enough thermal radiation to cause vegetation within 1, 000 to 1, 500 kilometers to go up in flames, " report Gulick and his colleagues.

The rock particles returning to Earth ignite plant matter even several thousand kilometers away, as coal deposits in the Chicxulub drill core reveal. The researchers suspect that these fire relics were either transported by air or were swept from the sea into the crater. Many of the carbon particles were formed immediately after impact, but others testify to fires that took years to come.

Tsunamis and tidal waves up to Illinois

At the same time, just a few minutes after the impact, the first tsunami raced through the Gulf of Mexico. The trigger for this was the collapse of the approximately 100 kilometer primary crater and the associated formation of the crater ring. The abrupt displacement of these large amounts of rock caused tsunamis, which reached the farthest reaches two to three hours after the impact, the researchers said. In the north, the water could have penetrated to the height of today's US state of Illinois into the country.

Indications for this flooding are provided by deposits of tens of meters in the Chicxulub Crater, which were deposited by the water thrown back at the coast. The first of these back-sweeping waves led to an inundation of the crater an hour after the impact, as Gulick and his team report. The water on the crater rim rose more than a kilometer.

But in the first tsunami, it was not: "The Chicxulub impact generated magnitude 10 to 11 earthquakes and these seismic shocks also led about 2, 000 kilometers away to local Seichen, " report Gulick and his team. Even far away from the coast, whole areas could have been flooded.

"First grilled, then frozen"

This makes it clear: even in its first hours, the Chicxulub impact unfolded an enormous destructive power. Within a radius of several thousand kilometers around the crater, only the short-term consequences of the impact could have destroyed almost all life. "Not all dinosaurs died that day, but many of them, " says Gulick.

The rest was done by the impact winter, which lowered the global mean temperatures by several degrees and caused a dimming of the sun for years. For many organisms on Earth, this was a fatal combination. "They were first grilled, then frozen, " said Gulick. (Proceedings of the National Academy of Sciences, 2019; doi: 10.1073 / pnas.1909479116)

Source: University of Texas at Austin

- Nadja Podbregar