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SAN FRANCISCO — In a sand drift on Mars, NASA’s Curiosity rover discovered … sand.

At a meeting of the American Geophysical Union here, scientists working on the mission talked about the analysis of the first soil sample.

John P. Grotzinger, the project scientist, inadvertently set off expectations of a major discovery when he told National Public Radio a couple of weeks ago that the data was “one for the history books.”

On Monday, Grotzinger said he was referring to the richness and quality of the data coming from Curiosity’s sophisticated instruments on the soil sample, not that it contained a major discovery. Grotzinger and other Curiosity scientists said their analysis did not provide definitive evidence for the building blocks of life as some had speculated.

“I think certainly what I’ve learned from this is that you have to be careful about what you say and even more careful about how you say it,” Grotzinger said. “We’re doing science at the speed of science. We live in a world that’s sort of at the pace of Instagrams.”

By design, it was an unremarkable pinch of dirt, more to test their apparatus than to make discoveries.

Ken Edgett, principal investigator for a camera that takes close-up images, described the soil as fine sand. “It’s very dry-looking stuff, just what you’d expect,” he said. “The grain size is sort of like these artificial sweeteners in term of size, finer than sugar but coarser than something like flour. The surface of the drift was covered with coarser sand — more like size the salt grains on those big hot pretzels you can get.”

The mineralogical composition was similar to that found by the Spirit and Opportunity rovers during their years of exploration elsewhere on Mars, suggesting that this sample can serve as a baseline for what covers much of the planet.

An instrument, Sample Analysis at Mars, or SAM for short, heated the dirt to nearly 1,500 degrees Fahrenheit (800 degrees Celsius), and looked at the gases that escaped as the dirt burned. The most common gases were water vapor and carbon dioxide.

The Sam instrument also detected chlorinated methane — a small, simple compound that falls in the category of organics, which are the building blocks of life. However, the scientists said it was much too early to say that the soil itself contained organics.

The carbon could be vestiges of molecules that the spacecraft took to Mars from Earth, and the organics could have been generated by chemical reactions as the dirt was heated.

Whether the carbon could point to anything biological on Mars, “that’s well down the road for us to get to,” Grotzinger said.

With the complexities analyzing the voluminous data, “There’s not going to be one single moment where we all stand up and on the basis of a single measurement have a hallelujah moment,” Grotzinger said.