First to Suffer From Asteroid That Doomed Dinos: Plants

It wasn't so much the asteroid impact that killed 75% of the species on Earth some 66 million years ago, but the fact that, for the following two years, little, if anything, could grow. That's according to research offering the first in-depth study of dust particles thrown into the atmosphere when the asteroid struck off the coast of what's now Mexico. After feeding new and existing data into a computer model used to simulate the global climate after impact, researchers determined the asteroid pulverized granite and gneiss rock that was thrown into the atmosphere as silicate dust, per CNN and Reuters. According to researchers, the dust blocked out the sun, leaving plants unable to photosynthesize.

It was previously thought that sulfur released during the impact combined with soot from wildfires to block out the sun and trigger a sudden, massive drop in global temperatures. But the computer model—incorporating new sediment samples taken from North Dakota's Tanis fossil site, capturing a 20-year period in the aftermath of the impact—indicated silicate dust played a larger role. According to researchers, dust particles of 0.8 to 8 micrometers each, the right size to stick around in the atmosphere, totaled 2,000 gigatons, or more than 11 times the weight of Mount Everest, per Reuters. Forming a global dust cloud, the particles would've caused surface temperatures to drop by some 27 degrees Fahrenheit, but they also would've made photosynthesis impossible.

"Within a few weeks, months, the planet underwent a global shutdown in photosynthesis, which continued for almost two years," Cem Berk Senel, a planetary scientist at the Royal Observatory of Belgium (ROB) and lead author of the study published Monday in Nature Geoscience, tells CNN. "It collapsed the food web, creating a chain reaction of extinctions." Unable to use light energy to synthesize foods from carbon dioxide and water, plants would've shriveled and died, followed soon by the herbivores which relied upon them, and finally the carnivores who were left without prey. The same thing would've happened in aquatic food webs with the loss of phytoplankton at their base.

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"Fauna and flora that could enter a dormant phase ... and were able to adapt to a generalistic lifestyle—not dependent on one particular food source—generally survived better, like small mammals," explains study co-author Ozgur Karatekin, another planetary scientist at ROB, per Reuters. Photosynthesis likely resumed after two years, reaching "a complete recovery" within three to four years, Senel tells CNN. "While the sulfur stayed about eight to nine years, soot and silicate dust resided in the atmosphere for about 15 years after the impact," Karatekin says, per Reuters. It could've taken even longer, about 20 years, for Earth to reach pre-impact temperatures, according to the study. (More asteroid stories.)