Teghaza 001's 4.1 Billion Years Is a Minimum Age, Not a Birth Date

The Meteoritical Bulletin entry classes Teghaza 001 as a pyroxene-phyric shergottite. NASA's Jet Propulsion Laboratory (JPL) calls that the most common class of meteorite from Mars. When planetary scientist Yang Liu was first asked to look at the stone, JPL says, she "almost passed on the opportunity." It looked like a common shergottite, so she "decided to take a peek, anyway."

Then came the odd textures, the unusual minerals and, finally, zircon crystals. It was only after we started looking closely that we realized this meteorite is really unique, Liu said in NASA's release.

On Thursday, Oct. 29, the journal Science published the Science paper from Liu and 13 co-authors, describing a rock that "formed at least 4.1 billion years ago." Headlines turned that into an age. It is better read as a floor.

The database called it ordinary

The stone is rose-colored and weighs nearly 2 pounds (800 grams), NASA's release says. It came in eight stones, the largest about the size of a fist, per Reuters. Meteorite hunters found them in Mali's Sahara at the beginning of September 2022, about four years before the paper, according to the Meteoritical Bulletin entry. Reuters places the site roughly 21 miles (34 km) from the village of Bir Chali.

So how does anyone know a rock from the Sahara came from Mars? Not by looking at it. JPL says researchers at the University of New Mexico (UNM) identified it as Martian from its oxygen isotopes, which act as "geochemical fingerprints for different planetary bodies." Isotopes are versions of an element with slightly different masses, and the team matched this stone's mix to those in other Martian meteorites.

Carl Agee, director and curator of UNM's Institute of Meteoritics, said: I realized that this one was a little bit like Black Beauty, not exactly, but it resembled it in the oxygen isotope values.

The logic is worth seeing. A Martian label is a comparison against a reference set: the roughly 435 known Martian meteorites, plus, JPL says, mineral and chemical data from NASA's Viking landers and the Curiosity and Perseverance rovers. Matching is sturdier than eyeballing, and it was settled first.

A clock that reads a floor

Now the number. Zircon is a tough crystal that traps uranium when it forms. Uranium decays into lead at a known rate, so the ratio of lead to uranium works as a clock. Reuters says the team used exactly that in zircons from the rock.

The catch, as EarthSky put it in July: If the zircon minerals melt or are exposed to fluids, though, then their 'clocks' are reset to zero. A reset clock reads too young, hence the minimum. JPL ties it to an event: the rock "had been altered by Martian water sometime around 4.1 billion years ago, suggesting it originally formed even earlier." The paper's title says "≳4.1," and the abstract says "at least."

There is also a puzzle about which clock did the work. NASA's release credits in-situ rubidium-strontium dating in the lab of Caltech coauthor Francois Tissot, on a piece smaller than a fingernail, analyzing single grains on its surface. Reuters describes uranium-lead dating in zircon. Live Science, on the April preprint, said several decay measures in different minerals agreed on at least 4.1 billion years. The final paper was not available for this report, so which number came from which clock cannot be said here.

The sample size can be said, with a caveat. In the authors' 2025 Meteoritical Society conference abstract, not the final paper, the authors reported zircon lead-lead ages averaging "4122 ± 27 Ma (1 standard deviation; n = 10)." Ma is million years, and n = 10 is ten measurements. Six had concordant uranium-lead ages near 4163 ± 181, and four were "reversely discordant." The authors wrote that the age "reflects the alteration that added Na to zircons, and hence a minimum formation age." Na is sodium.

Plainly, that is ten spots in a rock that, per the same abstract, "experienced high shock levels," with zircons partly converted to a mineral called reidite. None of this makes the date wrong. It makes it a lower bound on a small data set, which is how the authors treat it.

Still, the floor is high. Reuters says the planets formed roughly 4.5 billion years ago, so the rock is at most about 400 million years younger than Mars.

Is it the oldest? That depends on what is counted.

Agee calls Teghaza 001 the oldest Martian igneous rock ever found by a huge margin. Igneous means it cooled from molten rock. The Black Beauty family holds older individual grains, though, and Reuters says the Antarctic meteorite ALH84001, once assessed at about 4.5 billion years, now has a similar age, with Teghaza 001 likely the older. JPL counts it among the three most ancient Martian meteorites, about 0.7% of the roughly 435 known.

Even the era's name wobbles. UNM's release puts the Pre-Noachian at approximately 4.5 to 4.1 billion years ago, Wikipedia gives the Noachian as probably 4100 to 3700 million years ago, and the authors' companion paper says "Noachian hydrosphere." Teghaza 001 sits on a boundary whose own dates are uncertain.

What one stone can and cannot say about water

The evidence for fluids is the sturdiest part. Liu told Reuters that "multiple lines of evidence in Teghaza 001 suggest Mars' surface had water at more than 4.1 billion years ago," reflected in hydrogen isotopes in phosphate and oxygen isotopes in minerals and bulk samples. The abstract says the rock reacted with "fluids enriched in 18O" before an impact ejected it.

The companion paper in Science Advances, published in June, gives a minimum D/H ratio for Mars' water at 4.1 billion years ago of about twice that of Earth's seawater. D/H compares deuterium, a heavier hydrogen, with ordinary hydrogen; the lighter kind escapes to space more easily, so a high ratio means a lot was lost. The authors say that supports rapid hydrogen loss from Mars' early atmosphere.

Where was the water? Sources split. Reuters and JPL describe fluids percolating into the crust and mixing with molten rock, as occurs on Earth (Reuters also says the evidence points to surface water). Agee goes further. In UNM's release, he describes an Earth-like environment, with fluids coursing over the surface and volcanoes creating hydrothermal systems. The abstract supports reactions in ancient crust; it does not put rivers on the surface. Agee's reading goes further than that wording, and the difference matters for headlines that said "Earth-like."

Does it mean life? No. Co-author Lee Saper of NASA's Ames Research Center told Reuters the findings "lend support to the idea that early Mars had the necessary ingredients and conditions to harbor life, but do not directly answer the question of whether there was life on Mars," and that conditions were waning rapidly. UNM's release notes domains with high manganese, which Agee says rovers look for as an indicator of environments conducive to life; Saper's caution still stands. The rover-side evidence is a separate line: Perseverance Finds Complex Organic Carbon in Martian Mudstone, a June 25 piece on this site.

The blunter caution came from outside the team, from a researcher not involved. He told Live Science:

"I would caution that all of these arguments would have been based on a single small stone."

James Day, professor of geosciences, Scripps Institution of Oceanography, UC San Diego

Then there is the address problem. JPL says scientists identified 13 locations on Mars matching the rock's mineralogy and chemistry, in the "cratered southern highlands" seen by NASA's Mars Reconnaissance Orbiter; Reuters says possibly near Hellas Basin, per Liu. But "No one will ever know exactly where the meteorite originated on Mars," JPL says.

Anya Udry of the University of Nevada, Las Vegas, also not involved, said in Scientific American: Mars is a complex planet, and this meteorite is really cool, but we don't know exactly where it came from, so this is really another example of why we need to bring back samples. Saper counters that it is our first piece of Martian crust from a part of Mars we've never had a sample of before.

The paper is not new, exactly. A preprint with the same age went up on the ESS Open Archive on April 14, 198 days earlier, before peer review. The Science Advances companion paper came out in June, and Saper gave a talk at the Goldschmidt conference in Montreal on July 14, per EarthSky. What Thursday's paper adds is the review: other specialists have now tested the argument that 4.1 is a floor.

We've only scratched the surface, Liu said, and it is nearly literal. One of the dating methods, Tissot's in-situ rubidium-strontium work, used a piece smaller than a fingernail, out of about 800 grams of stone. Tissot says his lab is one of very few able to run that kind of in-situ dating, and the first to use it on a meteorite this old. The rest of the checking waits for other labs.