Classic detective fiction mysteries work because nearly every character ends up being a murder suspect. The extinction of non-avian dinosaurs is similar to this. The impact and aftermath of Chicxulub has created a wide range of potentially lethal suspects. Who? Huge fireball and tsunami? Is the climate changing rapidly? Global wildfires? A darkened sky that stopped photosynthesis? all of the above?
Modeling these effects in conjunction with data on extinction patterns has led to differing opinions about what was the decisive factor in the extinction of so many species. In the latest study of the end-Cretaceous extinction, a team of scientists based primarily in Brussels reexamined the sediment deposited in the aftermath of the impact and found that much of the debris came from fine dust. discovered. When that dust is incorporated into climate models, global temperatures drop by up to 25 degrees Celsius and photosynthesis ceases for almost two years.
dust to dust
A lot was happening in the atmosphere in the years after the impact. Debris kicked up by the impact would have re-entered Earth’s atmosphere, burning up into fine rocks and sulfur-rich particles in the process. The heat generated by this process would have caused massive wildfires and produced large amounts of soot. And all of that was stirred up along with debris from the impact that remained in the atmosphere.
This has led to the idea of an “impact winter” in which little sunlight reaches the Earth, causing temperatures to drop dramatically and photosynthesis to halt. Soot, rock debris, and sulfur-rich particles, all three of the main components of atmospheric dust, are believed to be responsible, but modeling has shown that levels are low enough to have an impact in winter. The question has arisen as to whether dust exists.
To better understand what’s going on, the researchers behind this new paper look at the deposits at a place called Tanis in North Dakota, where tsunami debris washed up on the shore shortly after the impact. was re-examined. There are also shocked quartz crystals that would have arrived directly at the scene from the impact within hours. Above these layers of impact debris is a layer of iridium-rich dust, mostly composed of silicate material that was blown away from the impact site and gradually settled over the following years. I am.
The researchers scanned this layer with a laser diffraction imager, which allowed them to estimate the size of the dust particles that formed these deposits. The average particle size was found to be significantly smaller than that assumed to be produced by impact in most studies. This small size affects how long the dust stays in the atmosphere and how it interacts with sunlight.
To understand how it affects events after the Chicxulub impact, researchers plugged it into a global climate model.
big cold
The researchers allowed the model to reach a steady state of continental composition and atmospheric composition at the end of the Cretaceous. Depending on the season, this resulted in global temperatures between 15°C and 19°C. Then, based on estimates generated elsewhere, they injected large amounts of material into its atmosphere.18 silicate powder 10g16 soot grams and 1017 grams of sulfur dioxide. For comparison, we also simulated each of these impact debris separately.
The effect was dramatic. The most extreme runs of climate models have lowered temperatures by as much as 25 degrees Celsius. Conditions remained “severe” for at least five years, with temperatures remaining below pre-impact conditions for a total of approximately 20 years.
Each type of material has a different half-life in the atmosphere and interacts with light (both incoming sunlight and infrared radiation traveling from Earth to space) in different ways. As a result, the effects of their mixture are distinct from the effects of a single type of particle in the atmosphere. And the finer dust used in this study remained in the atmosphere more than twice as long as the coarser dust studied in previous modeling.
In addition to the rapid changes in climate, researchers estimate that photosynthesis would cease to exist globally in less than two weeks. A partial return in the austral summer would result in a global observation hiatus for at least 1.7 years. (This is consistent with the extinction being more severe in the Northern Hemisphere.) Photosynthesis remained suppressed for four years after the impact.
This result helps clarify why scientific mystery novels are so difficult to solve. Small changes in the size of the particles launched by Chicxulub dramatically altered the climate over the next few years. We hope that over time, data from other sites will help resolve the complex events that occurred after the collision.
Nature Geoscience, 2023. DOI: 10.1038/s41561-023-01290-4 (About DOI).
