When it comes to mass extinction, the size of meteorites doesn’t matter.
(ORDO NEWS) — A new study shows that it is the composition of the rock that the meteorite crashes into, not its size, that triggers the extinction-level event.
It’s a well-known story from our planet’s past: A giant space rock crashes into Earth, causing a catastrophe that ends in a mass extinction. One might think that the size of the incoming impactor is important in determining which strikes will cause such massive destruction. But new research suggests that something else may matter more: The composition of the ground where the meteorite hits.
The paper, published December 1, 2021 in the Journal of the Geological Society, is dedicated to explaining why some meteorite impacts cause mass extinctions while others do not. For example, the famous impact that killed the dinosaurs and left the Chicxulub crater was much smaller than many other impacts that did not lead to mass extinction of species. Why might this be so?
It’s all about the dust
An international team of researchers, including experts in mineralogy, climate, asteroid composition and paleontology, has addressed this issue by studying 33 collisions over the past 600 million years. In particular, they studied minerals contained in a huge amount of dust, which is thrown into the atmosphere by an incoming meteorite. This dust can greatly change the Earth’s climate – and it is this climate change that researchers believe is the main cause of mass extinctions after collisions.
This study uncovered something intriguing: Whenever a common mineral called potassium feldspar (also called K-feldspar or Kfs) was present in high concentrations in the rocks that the meteorite crashed into, the collision resulted in a mass extinction.
In the 33 collisions they studied, this happened regardless of the size of the impactor, which means that small meteorites that hit areas rich in Kfs are more likely to cause a mass extinction than large meteorites that hit regions without a lot of Kfs.
Why is this happening? It turns out that Kfs is a mineral called an ice nucleator, which means that ice forms around it, creating ice crystals in the atmosphere. These ice crystals have a profound effect on clouds, which play a vital role in balancing the Earth’s climate. In particular, Kfs makes clouds more transparent and allows more sunlight to pass through, warming the Earth’s surface.
It also has side effects that could further disrupt the Earth’s climate. Usually, when the climate warms, the ice crystals in the clouds melt, which reduces their transparency, blocking sunlight and balancing the climate. But an excess of Kfs in the atmosphere makes it harder for ice crystals in clouds to melt, which could further exacerbate global warming.
In the immediate aftermath of any major impact, the massive amount of ejected dust can cause cooling as it blocks sunlight. But the researchers say this effect, called impact winter, is small and often lasts less than a year. A more significant effect, they say, occurs over the course of 1,000 to 100,000 years, as dust rich in Kfs continues to seed ice crystals in the atmosphere.
Ultimately, impacts in regions of the Earth rich in Kfs cause long-term global warming, which in turn is associated with mass extinctions. Thus, it appears that the mineralogy of the impact site is more important than the size of the impactor.
“When we put all the data together, it turned out that life continued as normal during the fourth largest impact [in the study], with a crater diameter of 48 kilometers [30 miles], while an impact half the size was associated with a mass extinction of just 5 million years ago,” study co-author Chris Stevenson of the University of Liverpool in the UK said in a press release.
This work “demonstrates that not the size of the impact, but the content of Kfs in the ejecting shell is correlated between meteorite impacts and mass extinction events,” the article says. The next step, of course, is to determine exactly how extinctions occur during these warming episodes and how long the effect lasts.
The article ends on a deep – and perhaps ominous – note: “The available evidence suggests that, to this day, only meteor impacts have been able to change the mineralogy of the atmosphere with such (geological) suddenness and persistence,” the article says.
But now everything has changed. Humans today have the ability to control climate change – and mass extinctions – through the changes we make to our atmosphere in ways that previously could only be achieved through giant impacts. And this imposes on modern society a certain responsibility for what power we have over our planet.
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