ORONO — University of Maine professor Alicia Cruz-Uribe and her colleagues were analyzing a box of rock samples from Mars when they made an unexpected discovery. They would confirm that one sample came from one of the oldest Martian meteorites ever found on Earth.
While examining samples to determine their age, the group selected one from Teghaza 001, an ancient Martian meteorite found by Sahrawi prospectors in the Sahara Desert in 2022. Until recently, little was known about the age and origins of the meteorite.
Most Martian meteorites found on Earth are no more than about 2 billion years old. But in a lab at the California Institute of Technology in summer 2025, Cruz-Uribe and her colleagues measured isotopes showing that Teghaza 001 is 4.1 billion years old.
Only two other known Martian meteorites are older than 4 billion years: Allan Hills 84001 and NWA 7034, also known as Black Beauty.
“I think we actually jumped up and down; full on dance party in the lab,” Cruz-Uribe, Edward Sturgis Grew Professor of Petrology and Mineralogy, said.
In a new study published in Science, Cruz-Uribe and her colleagues confirmed not only Teghaza 001’s age but also that it dates back to the formation of Mars’ crust and mantle — offering a rare window into the planet’s geologic history.
“When you add a third sample, and its geochemistry is really unique compared to the other samples that we have, it lets us see a different part of Mars’s ancient history in terms of what the mantle looked like and what the different mantle sources were on Mars,” Cruz-Uribe said.
A new method for dating rocks
The study is part of a multiyear research project on the formation of Mars’ crust by Cruz-Uribe and colleagues from Caltech, UCLA and the University of New Mexico. It involved a new method Cruz-Uribe developed for dating rock samples.
The technique involves firing a laser beam one-sixth the width of a human hair to drill holes into a sample. It uses helium gas to carry material removed by the laser through a tube and into a mass spectrometer — a machine that allows elements to be separated by mass. Chemical reactions inside the instrument separate the elements so researchers can measure the sample’s composition.
Similar dating methods have been used by other scientists to identify isotopes of uranium and lead, but Cruz-Uribe’s method is unique because it looks for rubidium and strontium. By looking for different elements, scientists can date minerals other than those containing uranium and lead, she said. That was crucial for dating feldspar minerals in Teghaza 001.
At Caltech, Cruz-Uribe and her colleagues discovered that the rubidium-strontium age of Teghaza 001 was the same as the uranium-lead age for zircons from the meteorite.
“When we can’t date a rock by one method, maybe the rubidium-strontium can fill in the gaps,” Cruz-Uribe said. “The other thing that is unique about this method is that it was created specifically for the mass spectrometer at Caltech in the lab of my colleague François Tissot, which is capable of high precision analyses of the isotopes of rubidium and strontium.”
Rubidium-strontium has been one of the most popular geochronologic systems used by scientists for the last six decades, but traditional methods involved weeks, if not months, of chemistry and analysis that would destroy samples. By using laser ablation coupled to mass spectrometers, scientists can save time and preserve their samples, Cruz-Uribe said.
“Instead of taking your bulk sample and dissolving it and separating out rubidium and strontium, this allows you to put your sample into the laser chamber, pick your spot, drill a hole with the laser, and then do the separation chemistry inside of the mass spectrometer,” she said. “A single laser spot typically takes less than one minute.”
The samples used in the study are held at the Institute of Meteoritics at the University of New Mexico and total 22 grams of Teghaza 001. The meteorite’s primary mass, weighing 442 grams, is held by the Maine Mineral & Gem Museum in Bethel.
“We really appreciate having this type of resource in the state of Maine, and we appreciate their generosity in sharing samples with researchers when they need them,” Cruz-Uribe said. “The Maine Mineral and Gem Museum has recently loaned us an additional piece of Teghaza 001 so that we can continue work on this sample both at Caltech and also at UMaine.”
Cruz-Uribe has analyzed this additional sample of Teghaza 001 in UMaine’s MicroAnalytical Geochemistry and Isotope Characterization Laboratory, or MAGIC Lab.
UMaine students applying the research
In addition to studying Martian meteorites, Cruz-Uribe and her students are using her new method to date rocks in Maine, particularly western Maine, to learn more about the state’s geological history and composition.
“Most of the rocks in Maine were studied back in the ‘50s and ‘60s, and a lot of the fundamental work on a large portion of the state was done before the development of any of the modern geochronology tools that we have now,” Cruz-Uribe said, “so we are able to add a huge amount of information to better understand the tectonic history of Maine.”
UMaine students have also helped prepare the meteorite samples Cruz-Uribe and her colleagues have studied in their multiyear project.
“They contribute to this science in real and fundamental ways, and they deserve credit for that,” she said. “We are excited to embody UMaine’s mission as a learner-centered R1 institution by giving students access to cutting-edge geochemistry and geochronology experiences during their undergraduate and graduate educations.”