Could Cataclysmic Asteroid Impacts Have Triggered Snowball Earth?
If you were to travel back in time millions of years ago, you would find Earth transformed into a frozen wasteland, similar to the icy planet Hoth from Star Wars. This phenomenon, known as Snowball Earth, occurred at least twice over 600 million years ago. Scientists have long been puzzled by what could have caused this extreme global cooling. While theories like rogue volcanism and supercontinental destruction have been proposed, a new study published in Science Advances suggests that cataclysmic asteroid impacts may have played a significant role.
When large asteroids collide with Earth, they release massive amounts of rock into the atmosphere. Some of this rock contains sulfur-bearing minerals, which turn into sunlight-reflecting aerosols in the stratosphere. If enough aerosols are present, the planet can rapidly cool down. The researchers behind this study simulated the injection of sulfate aerosols into the stratosphere at different concentrations, similar to what would be generated by a massive asteroid impact. They found that while warmer climates could withstand an asteroid impact without freezing over, already cold regions could be pushed into a Snowball state.
Although there is currently no geological evidence to support this theory, the study suggests that asteroids should be considered as potential suspects in the case of Snowball Earth. Thomas Gernon, a geoscientist at the University of Southampton who was not involved in the study, describes it as a “very interesting thought experiment.” The study also highlights the importance of developing a planetary defense system to prevent dangerous asteroids from reaching Earth.
The consequences of a large impact followed by global glaciation would be catastrophic for complex life and could potentially lead to the extinction of humanity, warns study author Minmin Fu, a climate dynamicist at Yale University. The impact would block out sunlight, causing the planet to cool and ice to form. As more ice accumulates, it reflects even more sunlight back into space, further cooling the planet. Once a certain icy threshold is reached, Earth becomes a snowball.
While not all scientists agree that Earth has experienced complete global glaciation, the presence of peculiar geological features, such as compressed layers of sediment and rocky debris typically associated with glaciers, suggests that Earth was indeed covered in snow and ice at least twice between 720 and 635 million years ago. Understanding why these events occurred and why they ended is crucial, as shortly after the second thaw, the Cambrian Explosion took place, marking a significant increase in complex life forms.
Volcanoes have been considered as potential culprits for Snowball Earth, with theories suggesting that they released excessive amounts of sulfur dioxide or reduced carbon dioxide emissions, leading to cooling effects. However, it remains unclear whether volcanoes could have erupted sulfur dioxide quickly enough or experienced a significant drop in carbon dioxide output to trigger Snowball Earth. On the other hand, asteroid impacts have an instantaneous effect, rapidly releasing sulfates into the atmosphere.
To test their asteroid theory, the researchers created detailed simulations of different periods in Earth’s history, each with varying atmospheric and oceanic conditions. They injected plausible amounts of sulfur dioxide gas into the stratosphere, similar to what would be produced by an impact like the one that caused the Chicxulub crater 66 million years ago. The results showed that adding sulfur dioxide to cooler periods in Earth’s history, such as the Neoproterozoic era and the Last Glacial Maximum, could lead to global sea ice coverage in less than a decade.
However, to confirm this theory, scientists would need to find a crater similar in size to Chicxulub or remnants of an impact containing high levels of sulfur dating back to the onset of these icy periods. While erosion and other geological processes may have made it challenging to find such evidence after billions of years, researchers remain hopeful. Thomas Gernon describes the study as “tantalizing,” but he remains skeptical until concrete geological evidence is discovered.
In conclusion, this study presents a compelling argument for the role of cataclysmic asteroid impacts in triggering Snowball Earth. While it remains a theoretical exercise for now, the study emphasizes the need to keep an open mind and acknowledges the significant impact that asteroids can have on Earth’s fate, as demonstrated by events like the Chicxulub impact. Further research and geological evidence are necessary to fully understand the history of Snowball Earth and its implications for life on our planet and beyond.
