However, until now, scientists had lacked fossil evidence of this impact winter, because this severe cold spell might have only lasted months to decades, too short a time period to be captured in a fossil record stretching across millions of years. In addition, many of the algae that produce the chalky fossils scientists use to estimate ancient ocean surface temperatures went extinct during the end-Cretaceous mass extinction.
"Our study is the first to show that this period of darkness and cold indeed took place," Vellekoop told Live Science.
Vellekoop and his colleagues focused their research on rocks exposed along the Brazos River between Waco and Hearne, Texas. These rocks originated from sediments deposited on the floor of a sea that existed in the area during and after the end of the Cretaceous.
The scientists analyzed organic compounds from microbes known as Thaumarchaeota, which adjust the composition of fat molecules in their membranes as sea surface temperatures change.
The researchers investigated organic compounds from Thaumarchaeota in Bravos River sediments of the same age as the Chicxulub impact. These sediments held coarse layers of broken shells — possibly traces of a post-impact tsunami — and anomalously high concentrations of iridium, a metal rare on Earth's surface but more common in space rocks.The findings suggest ocean temperatures fell dramatically after the impact, cooling from about 86 degrees F (30 degrees C) to about 73 degrees F (23 degrees C).
"Working on an event 66 million years ago, it is incredible that we could resolve sea water temperature changes within decades," Vellekoop said.
The most important implication of these findings "is that they demonstrate how devastating large meteorite impacts can be," Vellekoop added. "Our study confirms that such impacts can cause a so-called 'impact winter,' a global darkness lasting for years."
The researchers now aim to verify these results at other sites. The scientists detailed their findings online May 12 in the journal Proceedings of the National Academy of Sciences.
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