Death of an ancient asteroid may have set the scene for an explosion of life on Earth
A new study suggests that the disintegration of a massive asteroid that once orbited between Jupiter and Mars could have triggered an ice age on ancient Earth, that dramatically altered the evolution of life on our planet. Debris from the asteroid may have showered the inner solar system with dust, blocking a portion of the Sun’s light for millions of years and creating climate zones on Earth in the process.
Scientists had previously discovered evidence for an ice age that gripped ancient Earth roughly 466 million years ago, in rocks that once rested on the ocean floor. The rock samples revealed that the sea level was relatively low at this time, indicating that a large amount of Earth’s water was bound in glaciers and ocean ice.
A new paper argues that a driving factor for the onset of this event – known as the Ordovician ice age – could have been the destruction of a major asteroid.
According to the authors of the study, an approximately 150 km (93 mile)-wide asteroid orbiting in the main asteroid belt broke apart 466 million years ago. The destruction of the asteroid would have inundated the solar system with vast amounts of dust. A fraction of this debris would have inevitably made its way to Earth and entered the atmosphere, possibly kicking off a powerful cooling effect.
Earth is constantly being bombarded with small meteors and space particles, and it is estimated that roughly one percent of the dust in our planet’s atmosphere is of extraterrestrial origin. However, in the wake of the destruction of the asteroid, the researchers believe that the quantity of material entering Earth’s atmosphere from space would have dramatically increased.
"Normally, Earth gains about 40,000 tons of extraterrestrial material every year," says Philipp Heck, an author of the new study, curator at the Field Museum of Natural History in Illinois, and associate professor at the University of Chicago. "Imagine multiplying that by a factor of a thousand or ten thousand."
To contextualize that, in a typical year, one thousand semi trucks' worth of interplanetary dust fall to Earth. In the couple of million years following the collision, it'd be more like 10 million semis. The sheer amount of dust present in the atmosphere would have blocked a significant amount of the Sun’s warming radiation, triggering a gradual cooling of the planet.
The team discovered evidence of the space debris that may have triggered the cooling in 466-million-year-old rocks from sites in Sweden and Russia that once rested on the sea floor. Samples of these rocks were exposed to acid which melted the stone, leaving only extraterrestrial material behind. The researchers then analyzed the chemical makeup of the remnants to determine their origin.
They also measured the content of rocks from the seafloor, looking for specific forms of atoms, or isotopes, that would indicate material that had been exposed to and altered by the interplanetary space environment.
According to the scientists, the results of these experiments supported their hypothesis that the influx of material from a shattered asteroid reached Earth at the same time as, and indeed may have triggered the Ordovician ice age. The team argue that enormous amounts of dust and chunks of the shattered asteroid would have continued to rain down on Earth’s atmosphere for roughly two million years following its destruction.
The effects of the subsequent climate change, though profound, were not as sudden as the changes that led to the extinction of the dinosaurs following the asteroid impact in the Cretaceous-Paleogene period. Instead, life on Earth had time to adapt to the new ecological niches created by the shifting temperatures across the globe. In short, life was given a chance to diversify.
That said, human-led climate change is once again causing the world to change at an alarming rate. Experts have therefore considered the prospect of anchoring asteroids at stable orbital points around the Earth, where their dust would reflect a portion of the Sun’s radiation, thus offsetting the greenhouse effect that is currently warming the planet.
The authors of the new study hope that their data on the asteroid that prompted the Ordovician ice age could help researchers determine how realistic the "captive asteroid" approach could be, by informing their models with real-world data.
The paper on the study has been published in the journal Science Advances.