The asteroid impact that wiped out most dinosaurs 66 million years ago didn’t just cause immediate devastation; it also triggered nearly two years of global darkness. According to findings presented by scientists from the California Academy of Sciences at the American Geophysical Union (AGU), this extended period without sunlight contributed to a cascade of extinctions and environmental changes that reshaped life on Earth.

The colossal asteroid that struck the Yucatán Peninsula left behind the Chicxulub crater, a depression over 150 kilometers (93 miles) in diameter. The impact released an immense force equivalent to billions of atomic bombs, instantly igniting wildfires that raged across continents and filled the atmosphere with fine soot and dust. This atmospheric pollution, dense with particles from these fires, blocked sunlight, preventing photosynthesis and plunging Earth into what scientists call a “nuclear winter” scenario.

Lead researcher Peter Roopnarine, a curator of geology at the California Academy of Sciences, explained that global wildfires likely released enough soot to block sunlight almost immediately, preventing photosynthesis. For nearly 700 days, the lack of sunlight prevented plants and photosynthetic organisms from producing food, which in turn disrupted the entire food chain. Marine ecosystems were similarly affected, as the reduction in sunlight led to the collapse of marine plankton populations, an essential food source for many marine species.

Roopnarine and his team estimated that regions such as Hell Creek—an area rich with fossils from the end of the Cretaceous period and spanning parts of modern-day Montana and the Dakotas—likely remained dark for up to two years. This prolonged darkness, combined with plummeting temperatures due to the blocked sunlight, affected all ecosystems worldwide. It was estimated that ecosystems could potentially recover from a dark period of about 150 days, but at around 200 days of darkness, irreversible changes and extinctions started to take place. After 650–700 days of darkness, up to 81% of species had vanished, with around 75% of life on Earth extinguished

Alongside darkness, the asteroid impact led to massive acid rain and other environmental changes that further altered Earth’s atmosphere and oceans. Acid rain devastated plant life, while the decline in marine plankton affected the food supply for marine animals, causing extensive marine extinctions. However, while the event marked the end for many species, including the non-avian dinosaurs, it opened new evolutionary pathways. With the dinosaurs’ extinction, mammals that had previously existed in minor roles began to diversify and dominate the ecosystem. Over millions of years, this shift would lead to the rise of mammals and, ultimately, human evolution.

The extinction event caused by the asteroid impact serves as a reminder of the planet’s vulnerability to extraterrestrial events. While it led to the collapse of Earth’s prehistoric ecosystems, it also cleared the way for new life to flourish, significantly reshaping life on our planet. The discovery underscores the significant environmental impact such events can have, leaving a lasting legacy on Earth’s evolutionary path.