There’s always a lot of extraterrestrial dust floating down to Earth, but this dust is normally only a tiny fraction of the other dust in our atmosphere such as volcanic ash, dust from deserts and sea salt. But when a 93-mile (150 km) wide asteroid broke apart in the main asteroid belt between Mars and Jupiter some 466 million years ago (the middle of the Ordovician period), it created way more dust than usual.
“Normally, Earth gains about 40,000 tons of extraterrestrial material every year. Imagine multiplying that by a factor of a thousand or ten thousand,” said Dr. Philipp Heck, a curator at the Field Museum and researcher at the University of Chicago.
To contextualize that, in a typical year, one thousand semi trucks’ worth of interplanetary dust fall to Earth. In the couple million years following the collision, it’d be more like ten million semis.
“Our hypothesis is that the large amounts of extraterrestrial dust over a timeframe of at least two million years played an important role in changing the climate on Earth, contributing to cooling,” Dr. Heck said.
“Our results show for the first time that such dust, at times, has cooled Earth dramatically, added Dr. Birger Schmitz, from Lund University and the Field Museum.
“Our studies can give a more detailed, empirical-based understanding of how this works, and this in turn can be used to evaluate if model simulations are realistic.”
To figure it out, the team looked for traces of space dust in 466-million-year-old rocks, and compared it to tiny micrometeorites from Antarctica as a reference.
“We studied extraterrestrial matter, meteorites and micrometeorites, in the sedimentary record of Earth, meaning rocks that were once sea floor,” Dr. Heck said.
“And then we extracted the extraterrestrial matter to discover what it was and where it came from.”
Other studies had already established that our planet was undergoing an ice age around this time.
The amount of water in the Earth’s oceans influences the way that rocks on the seabed form, and the rocks from this time period show signs of shallower oceans — a hint that some of the Earth’s water was trapped in glaciers and sea ice.
Dr. Heck, Dr. Schmitz and their colleagues are the first to show that this ice age syncs up with the extra dust in the atmosphere.
“The timing appears to be perfect. The extra dust in the atmosphere helps explain the ice age — by filtering out sunlight, the dust would have caused global cooling,” Dr. Schmitz said.
Since the dust floated down to Earth over at least two million years, the cooling was gradual enough for life to adapt and even benefit from the changes. An explosion of new species evolved as creatures adapted for survival in regions with different temperatures.
The findings are published in the journal Science Advances.
Birger Schmitz et al. 2019. An extraterrestrial trigger for the mid-Ordovician ice age: Dust from the breakup of the L-chondrite parent body. Science Advances 5 (9): eaax4184; doi: 10.1126/sciadv.aax4184