From the geysers of Yellowstone National Park to the black smokers of mid-ocean ridges, interactions between hot rock and water are common on Earth. Now, researchers have studied a hydrothermal system created not by volcanism—a common culprit—but rather by a cataclysmic asteroid impact. By analyzing rock cores drilled from the Chicxulub crater, they found evidence that a hydrothermal system endured for at least 150,000 years after the impact. The warm, watery environment may have been a cradle for microscopic life, the team suggests.
Crash and Flow
Roughly 66 million years ago, an asteroid the size of a small city slammed into modern-day Mexico’s Yucatan Peninsula. The impact melted rocks, launched tsunami waves, and excavated an enormous crater. Groundwater would have percolated through the fractured landscape, previous analyses suggest, and now researchers have analyzed chemical and mineralogical evidence for such fluid flow in rock cores unearthed in 2016 from the crater’s “peak ring.”
David Kring, a planetary scientist at the Lunar and Planetary Institute in Houston, and his colleagues studied Chicxulub cores that had been split in half lengthwise. They found striking evidence that fluids had dissolved and remineralized some of the crater’s rocks.
“Essentially, the entire core of the crater, from the surface of the crater when it was formed to the bottom of our borehole, is hydrothermally altered,” said Kring.
In some of the cores, fiery orange sodium dachiardite and analcime ran through a darker gray background of impact melt–bearing breccia. In others, veins of quartz and epidote cut across multihued granites. “It’s the kind of thing that makes a petrologist’s mouth water,” said Kring.
Like Yellowstone, but Bigger
Boreholes drilled previously in other parts of the 180-kilometer-diameter crater also show signs of fluid flow, suggesting that Chicxulub’s hydrothermal system was pervasive. Using model estimates of the depth of the hydrothermal system, Kring and his colleagues concluded that fluid flow had altered roughly 140,000 cubic kilometers of Earth’s crust. That’s nearly an order of magnitude larger than the volume of the Yellowstone Caldera, the team calculated.
Chicxulub’s hydrothermal system would initially have been too hot to sustain life. But as time passed and the region cooled, microorganisms might have found a toe hold, said Kring. The “Goldilocks temperature” for thermophilic microbes is roughly 50°C to 120°C, and different portions of the crater would have been hospitable at different times. “As the system evolves, the regions suitable for microbial activity will migrate.”
Tiny Magnets Reveal Age
To determine how long the hydrothermal system in Chicxulub persisted, team member Sonia Tikoo, a geophysicist at Stanford University, analyzed tiny pieces of rock containing magnetite. This mineral records the polarity of Earth’s magnetic field, which changes over time.
If the crater had cooled relatively rapidly, all of its magnetite ought to exhibit the same polarity—the one corresponding to the time of the impact. (The next polarity switch occurred 150,000 years later.) However, Tikoo found that some of the magnetite exhibited the opposite polarity, meaning that the crater’s hydrothermal system must have persisted for at least 150,000 years. That timescale is a lower limit, said Tikoo. “It’s possible that it’s recorded multiple flips. We can’t rule that out.”
However, Chicxulub’s hydrothermal system might have been far longer-lived, other lines of evidence suggest. Previous research based on thermal modeling showed that underground temperatures still hovered around 90°C roughly 2 million years after the impact. Observations of manganese, an element carried by hydrothermal fluids, also suggested that groundwater was still being vented into the sea as late as 2.1 million years after the impact, Kring and his colleagues found.
These results were published last month in Science Advances.
Billions of years ago, when the cratering rate was much higher, hydrothermal systems would have dotted Earth and other solar system bodies after impacts, said Kring. “We envision the early Earth’s crust being permeated with these impact-generated hydrothermal systems.”
It’s possible that life originated in one of these warm, watery pockets, the team hypothesized. “Hydrothermal systems are wonderful habitats for microorganisms,” said Kring.
The same could have been true on other worlds. Next month, a Mars rover, Perseverance, will be launched from Florida’s Cape Canaveral Air Force Station and will begin a 7-month journey to the Red Planet as part of the Mars 2020 mission. Perseverance will land in Jezero crater, which was sculpted by flowing water far in the Martian past.
Perseverance’s many instruments will look for evidence of hydrothermal activity that might have persisted after the crater-forming impact. “Life on Mars is unlikely to exist on the surface,” said Horton Newsom, a planetary geologist at the University of New Mexico not involved in the research. “Evidence of it may be present deep down within Mars.”
—Katherine Kornei (@KatherineKornei), Science Writer