A drill hole in an ancient Martian rock has yielded something more complicated than a simple yes-or-no answer about life. NASA’s Curiosity rover has identified a broad mix of organic molecules on Mars, including compounds tied to sulfur, oxygen and nitrogen, along with chemicals that scientists see as important to life’s chemistry on Earth. One of the most intriguing signals came from a nitrogen-bearing molecule with a structure similar to compounds used to build DNA. Another was benzothiophene, a sulfur-containing molecule that had not been firmly confirmed on Mars before. That does not mean life once existed there. It does mean Mars can preserve fragile chemical clues for a very long time. “We think we’re looking at organic matter that’s been preserved on Mars for 3.5 billion years,” said Amy Williams, a geological sciences professor at the University of Florida who led the study and works on both the Curiosity and Perseverance rover missions. “It’s really useful to have evidence that ancient organic matter is preserved, because that is a way to assess the habitability …