The Chicxulub impact event was an enormous catastrophe that left a huge imprint on the Earth’s surface. Not only did it cause the mass extinction of the dinosaurs, it left a crater 180 km (112 miles) in diameter, and deposited a worldwide layer of concentrated iridium in the Earth’s crust.
But a new study shows that the impact also left its mark deep underground, in the form of a vast hydrothermal system that modified a massive chunk of the Earth’s crust.
The Chicxulub impact was catastrophic for life on Earth. When that huge comet—or asteroid—struck Earth, it set in motion a chain of events that changed the history of the planet.
It penetrated about 20 km (12 miles) into the Earth’s crust. It created a massive tsunami, ignited fires around the globe, and sent massive amounts of material into the atmosphere. Due to the carbon-rich and sulfur-rich nature of the impact site, the atmosphere became clogged with stratospheric soot and sulfate aerosols. Those materials persisted in the atmosphere, stifling photosynthesis and creating a global cooling that wiped out about 75% of Earth’s species, including all the non-avian dinosaurs.
But hidden out of sight, deep underground, is a vast hydrothermal system created by the impact. The nature of that system is only now coming to light.
A new study presents the details of this underground system. It’s titled “Probing the hydrothermal system of the Chicxulub impact crater.” The lead author of the study is David Kring at the Lunar and Planetary Institute (LPI). The paper is published in the journal Science Advances.
The Chicxulub crater is the most well-preserved large impact structure on Earth. It’s been studied extensively, including in 2016, when a team of researchers studied deep core samples of the ocean floor at the impact site, gathered by a drilling rig. Some of those samples came from 1335 meters (4380 ft.) beneath the sea floor. That was part of the International Ocean Discovery Program (IODP).
That program led to published research showing how Chicxulub’s peak ring was formed, and showing the displacement of rocks, where deeper granite bedrock was placed above sedimentary rocks by the energy of the impact. Numerous other studies flowed from the IODP work.
The team behind this new work focused on the chemical and thermal modification of the rock at the impact site. They deduced that the Chicxulub impact event created a vast underground hydrothermal system, larger than the Yellowstone Caldera, that was active for over 150,000 years.
“Imagine an undersea Yellowstone Caldera, but one that is several times larger and produced by the staggering impact event that resulted in the extinction of the dinosaurs,” said lead author Kring in a press release.
Some impact craters, including Chicxulub, create a peak ring. It’s a raised range of mountains inside the crater rim. The peak rings are uplifted by the rebound force of the impact, and they’re made of fractured rock. The rock in Chicxulub’s case is granite, lifted from a depth of 10 km (6 miles) in the Earth’s crust. The force of the impact and the uplifting caused the fracturing. That peak ring is further covered with impact debris, itself fractured and permeable, and both the surface debris and the uplifted crust were subjected to the effects of the hydrothermal system.
The researchers found evidence of underground rivers of water that were superheated by the impact, and driven upwards. Those subterranean rivers met with the boundary between the impact crater’s floor and the bottom of the ocean. There, the heated water met a 3 km (1.8 mile) pool of magma created by the impact, called the central melt pool. The water couldn’t penetrate that magma, and was forced around its edges. Then it percolated through all of the fractured rock, and was vented into the sea.
The hot water activity was particularly intense near the crater’s peak ring. The peak ring is 90 km (56 miles) in diameter. The team examined rock samples from that ring and found that the ring is riven with fossilized hydrothermal conduits. As the super-heated water flowed through these conduits 66 million years ago, it left its mark. The water deposited almost two dozen different types of minerals on the walls of these conduits, replacing the original minerals.
“Hot-fluid alteration was most vigorous in the permeable impact debris, but garnet crystals, indicating high temperatures, were found at different levels throughout the core,” explained former LPI Postdoctoral Researcher Martin Schmieder.
The types of minerals told the researchers a lot about the hydrothermal system. The temperature of the water had to be 300 C to 400 C (570 to 750 F.) That much thermal energy would’ve taken a long time to dissipate, so high temperatures must have persisted for a long time. The researchers used the magnetic polarity of the minerals to create a kind of “geomagnetic polarity clock” that measures the cooling time.
“Our results indicate that tiny magnetic minerals were created in the Chicxulub crater due to chemical reactions produced by a long-lived hydrothermal system. These minerals appear to have recorded changes in the Earth’s magnetic field as they formed. Their magnetic memories suggest that hydrothermal activity within the crater persisted for at least 150,000 years,” says co-author Sonia Tikoo from Stanford University.
There’s also ocean sediment at the impact site that’s unusually rich in manganese. The researchers point out that that’s also evidence of a long-lived hydrothermal system.
“Similar to mid-ocean ridges, venting from marine impact craters generates hydrothermal plumes that contain dissolved and slowly oxidizing manganese, which compared to background concentrations produced enrichments up to ten-fold in post-impact sediments over 2.1 million years at Chicxulub,” said co-author Axel Wittmann from Arizona State University.
This research is based on a single core sample of the peak ring, named borehole M0077A. But it’s still evidence. And not only of the geological consequences of the Chicxulub impact.
The authors say their findings from that borehole have some potential implications for the origins of life.
As lead author Kring points out, “The results suggest there was an approximately 300 kilometer-long string of hot water vents on the peak ring and additional vents scattered across the crater floor as impact melt cooled. Importantly, such hydrothermal systems may have provided habitats for microbial life.”
In their paper the authors write “Drilling results demonstrate there were sufficient habitats for microorganisms within the peak ring of the Chicxulub impact crater. The hydrothermal system created a network of porous, permeable niches perfect for microbial ecosystems.”
Research into extremophiles has opened our eyes to the potential for life to thrive in, and even arise from, extreme environments. This is where the comparison between the Yellowstone Caldera and the Chicxulub hydrothermal system play a role. The Yellowstone hydrothermal system contains abundant microbial life. And though the Yellowstone system was created volcanically, while the Chicxulub system was created by impact, the pair of systems are similar, and contain the same biological potential for life.
As Kring explains, “Our study of the expedition’s rock core from a potential deep Earth habitat provides additional evidence for the impact-origin of life hypothesis. Life may have evolved in an impact crater.”
The discovery of this massive and long-lived hydrothermal system could change our understanding of how life came to be on Earth. Scientists know that there’ve been thousands of similar impacts in Earth’s deep geological history. The hydrothermal systems they created may have provided the niche footholds that gave life a chance to get going.
In the conclusion of their paper the authors wrote: “The hydrothermally altered Expedition 364 core demonstrates that impact cratering is a fundamentally important heat engine in emerging planetary systems and that the geologically young Chicxulub crater is a suitable analog for terrestrial impact basins created almost 4 Ga ago. Impact-generated hydrothermal systems were prominent features on early Earth and wherever water exists in a planetary crust.”
They also wrote that “This model is transferrable to an early Mars and any exoplanetary system with similar conditions.”
Maybe we should be looking for exoplanets with ancient impact craters if we want to find life.
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