Two massive asteroid impacts 35.65 million years ago left huge craters but caused no long-term climate change, according to a University of California, Los Angeles (UCL) study analyzing isotopes in marine fossils. The findings highlight the stability of Earth's climate over geological time scales.
Two giant asteroids struck Earth about 35.65 million years ago but did not cause any lasting changes in Earth's climate, according to a new study by UCLA researchers.
The two rocks, both several miles across, struck Earth about 25,000 years apart, leaving behind the 60-mile-long (100-kilometer) Popigai crater in Siberia, Russia, and the 25-55-mile (40-85-kilometer-long) crater in the Chesapeake Bay in the United States - the fourth and fifth largest known planetary craters on Earth.
The new study, published in the journal Communications Earth & Environment, found no evidence of lasting changes in climate in the 150,000 years after the asteroid impact.
Researchers have inferred past climates by looking at isotopes (types of atoms) in fossils of tiny shelled organisms that lived in the ocean or seafloor at the time. The pattern of the isotopes reflects the temperature of the seawater when these organisms were alive.
Co-author Professor Bridget Wade (UCL School of Earth Sciences) said: "The most important thing about our results is that nothing really changed after the impact. We would have expected the isotopes to move in one direction or another, indicating that the waters were getting hotter or cooler, but that didn't happen. After these large asteroid impacts, in the long run, our planet seems to have stayed the same."
"However, our study will not detect short-term changes over tens or hundreds of years because the samples were collected every 11,000 years. On human timescales, these asteroid impacts would be catastrophic. They would produce huge shock waves and tsunamis, cause widespread fires, and large amounts of dust would were blown into the air, blocking out sunlight. Simulation studies of the larger Chicxulub impact that wiped out the dinosaurs also show that the time scale of climate change is much smaller, less than 25 years, so we still need to know what's coming and fund missions to prevent future impacts."
The research team, which included Professor Wade and earth sciences master's student Natalie Cheng, analyzed isotopes in more than 1,500 fossils of single-celled organisms called foraminifera, both those that lived near the surface of the ocean (planktonic foraminifera) and those that lived at the bottom of the ocean (benthic foraminifera).
The fossils, which range in age from 35.5 million to 35.9 million years old, were discovered in cores extracted from the Gulf of Mexico seafloor by the Scientific Deep Sea Drilling Project.
The two main impacting asteroids at the time were estimated to be 3-5 miles (5-8 kilometers) and 2-3 miles (3-5 kilometers) wide, respectively. The larger of the two asteroids created the Popigai crater, which is as wide as the height of Mount Everest.
In addition to these two impacts, existing evidence suggests that three smaller asteroids also struck Earth during this period - the late Eocene - suggesting a disturbance in the solar system's asteroid belt.
The researchers pointed out that previous studies of the climate at that time were inconclusive, with some studies linking asteroid impacts to accelerated cooling, and others linking asteroid impacts to warming temperatures.
However, these studies were of lower resolution, looking at samples over longer time intervals than 11,000 years, and their analyzes were more limited - for example, only the species of foraminifera that live on the seafloor were studied.
By using fossils that lived at different ocean depths, the new study provides a more complete picture of how the ocean responded to impact events.
The researchers looked at carbon and oxygen isotopes in a variety of planktonic and benthic foraminifera.
They found that about 100,000 years before the impact of the two asteroids, isotopic changes occurred, indicating that the surface ocean warmed by about 2 degrees Celsius and the deep water cooled by 1 degree Celsius. But no changes were found before or after the impact.
Inside the rock, the researchers also found evidence of two major impacts in the form of thousands of small droplets of glass or silica. This is formed when silica-containing rocks are vaporized by asteroids. The silica eventually enters the atmosphere, but solidifies into droplets as it cools.
Natalie Cheng, co-author of the paper and a graduate student in Earth Sciences, said: "Given that the Chicxulub impact may have caused a mass extinction event, we were interested in investigating whether a series of asteroid impacts during the Eocene also contributed to lasting climate changes. "We were surprised to find that these impacts did not cause a clear climate response. It is fascinating to interpret the climate history of the Earth from the chemical composition preserved in the microfossils. It is particularly interesting that we chose the foraminifera species and discovered the beautiful microspheroid specimens during the study."
Compiled from /ScitechDaily