Approximately 66 million years ago, an asteroid measuring about 10 to 12 kilometers in diameter impacted a sulfur-rich carbonate platform near present-day Chicxulub, Mexico. This event generated a crater nearly 180 kilometers wide, coinciding with the extinction of approximately three-quarters of all species in the fossil record, including non-avian dinosaurs.
The most significant destruction from this impact was concentrated around the Gulf of Mexico and adjacent areas. However, this localized devastation does not fully account for the global-scale extinction that occurred. The atmospheric changes resulted from the impact played a critical role in this widespread event.
The First Hours: Heat from Above
The impact ejected molten rock into the atmosphere on various ballistic paths. As these droplets solidified into glassy spherules and re-entered the atmosphere, they heated the upper air. Research by Douglas Robertson and colleagues, published in a 2013 paper in the Journal of Geophysical Research: Biogeosciences, estimated that this produced an infrared pulse at the ground comparable to an oven set to broil for a short time post-impact.
The extent of this heat pulse igniting widespread fires remains disputed. A 2009 study by Tamara Goldin and Jay Melosh in Geology posited that the falling spherules may have shielded the surface from much of their radiation. Other models indicate that fire ignitions occurred in some areas but not as a global firestorm.
The Years After: The Sky Stayed Shut
The longer-term consequences led to darkness and cold. The impact site contained rock rich in sulfate and carbonate, and its vaporization released sulfur into the stratosphere, forming aerosols that blocked sunlight along with soot from burning vegetation. This reduction in sunlight affected photosynthesis on land and in the ocean, causing temperatures to decline for years.
A 2014 study in PNAS identified evidence of rapid cooling, consistent with an impact winter rather than a gradual temperature decline. This aligns with the survival characteristics of species that persisted, which were typically small organisms capable of burrowing or living in water.
What the Newest Modelling Adds
Recent research by Cem Berk Senel and colleagues, published in 2023 in Nature Geoscience, utilized palaeoclimate simulations and grain-size measurements from the Tanis K-Pg boundary deposit in North Dakota. Their findings indicate a greater proportion of fine silicate dust, ranging from 0.8 to 8 micrometres, than previously acknowledged.
The simulations suggested this dust could remain in the atmosphere for up to 15 years, contributing to surface cooling of approximately 15 degrees Celsius and stalling photosynthesis for nearly two years. The authors emphasized that these results represent only a part of the ongoing debate regarding the different contributing factors to the extinction.
Why the Distinction Matters
The relationship between the impact and the extinction event is often oversimplified. While the 1980 discovery of an iridium layer by Luis and Walter Alvarez highlighted the connection to an impact, it did not clarify the mechanisms of extinction. The evidence suggests that atmospheric changes, rather than mere surface destruction, played a significant role in the global fallout from the impact.
Understanding the specific contributions of sulfur, soot, and dust, as well as the impact of the initial heat pulse, is essential for reconstructing this critical period in Earth’s history.
Source: spacedaily.com via Google News.
