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Tag: Geochemistry

  • A Planet Inside a Planet? Traces of Pre-Moon Earth Found Deep Below

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    If proto-Earth had all its parts and chemistry replaced to become the Earth we know today, can the two still be considered the same planet? That’s the planetary version of Theseus’s Paradox, an old philosophical puzzle about identity and perception. The popular consensus until recently was that Earth’s chemistry changed completely after a giant meteorite impact, leaving nothing behind from its proto-Earth days.

    A new finding suggests that conception may be wrong. In a Nature Geoscience paper published earlier this week, researchers report detecting a chemical signature that appears to have miraculously resisted change for billions of years. Specifically, the team—an international collaboration between the U.S., China, and Switzerland—found an odd imbalance of potassium isotopes in ancient rock samples. Chemical analyses revealed the anomaly couldn’t have emerged from any known geological processes on modern Earth.

    Theseus’s planet?

    Planetary scientists have long suspected that a Mars-sized meteorite slammed into Earth some 4.5 billion years ago. The impact triggered a literal, astronomical makeover, transforming what was once a rocky, lava-filled environment into the Earth we know today.

    The general understanding was that, over time, whatever materials or processes formed proto-Earth either transformed or were replaced by ones more familiar to researchers today. It was, of course, a reasonable explanation: that the “resetting” of Earth’s chemistry miraculously created the conditions that eventually led to life.

    A potassium anomaly

    Naturally, scientists are still hoping to learn more about our planet’s earliest days. For the new paper, the authors zoomed in on potassium. On Earth, the common element normally exists in a specific combination of potassium-39 and potassium-41, with a tiny portion of potassium-40.

    Previous work by the study’s lead authors, however, showed that extraterrestrial objects—such as meteorites—have distinct potassium profiles, typically with a slightly higher proportion of potassium-40.

    Building on this knowledge, the team dug deep into the oldest available rocks on Earth, such as powdered rocks from Greenland and Canada and lava deposits in Hawaii. At the lab, they ran the samples through various techniques in analytical chemistry.

    Surprisingly, the potassium profile they ended up with was unlike anything researchers had ever seen—neither on Earth nor in cosmic objects. In fact, the “deficit” of potassium-41 was so bizarre that spotting it was “like spotting a single grain of brown sand in a bucket rather than a scoop full of yellow sand,” the researchers told MIT News.

    An ongoing mystery

    Was there really no feasible, natural way for this chemistry to have emerged? Multiple simulations and follow-up investigations of all known meteorites and geological processes seemed to point to the same answer: no. According to the paper, the most viable explanation for this material’s existence is that it was left over from proto-Earth.

    “This is maybe the first direct evidence that we’ve preserved the proto-Earth materials,” Nicole Nie, study co-lead author and a planetary scientist at MIT, explained to MIT News. “We see a piece of the very ancient Earth, even before the giant impact. This is amazing because we would expect this very early signature to be slowly erased through Earth’s evolution.”

    That said, we may as well end up finding something, like an odd meteorite, with the same potassium anomaly, in which case the signature wouldn’t necessarily be the surviving remnants of proto-Earth.

    Either way, the findings demonstrate that there’s still a lot for us to learn about our own Earth—lessons that, perhaps, may guide us away from any missteps we’re making while studying things beyond Earth.

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    Gayoung Lee

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  • Scientists Just Discovered an Exotic New Element in Apollo-Era Moon Dust

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    Science has come a long way since NASA launched the Apollo 17 mission. Over the last 50 years, researchers have developed advanced technologies and techniques that far surpass those available in 1972.

    This progress is exactly what NASA was hoping for when the Apollo 17 astronauts—the last humans to set foot on the Moon—returned to Earth with more than 2,000 samples of lunar rock and dust. Some were squirreled away in the hopes that one day, better-equipped scientists could study the samples and make new discoveries.

    And that’s what a team of researchers led by James W. Dottin III, an assistant professor of Earth, environmental, and planetary sciences at Brown University, just did. Dottin and his colleagues analyzed the composition of samples taken from the Moon’s Taurus-Littrow valley. The findings, published last month in the journal JGR Planets, indicate that volcanic material in the samples contain sulfur compounds that are starkly different from those found on our planet.

    “Before this, it was thought that the lunar mantle had the same sulfur isotope composition as Earth,” Dottin said in a press release. “That’s what I expected to see when analyzing these samples, but instead we saw values that are very different from anything we find on Earth.”

    A discovery 50 years in the making

    After the Apollo 17 astronauts landed in the Taurus-Littrow valley, they extracted a 2-foot-long core sample from the lunar surface using a hollow metal instrument called a double drive tube. Once returned to Earth, this sample and many others like it remained sealed inside their tubes under the protection of NASA’s Apollo Next Generation Sample Analysis (ANGSA) program.

    In the last few years, NASA has begun accepting new research proposals to study the ANGSA samples. Dottin proposed analyzing sulfur isotopes using secondary ion mass spectrometry, a high-precision technique that wasn’t available when the samples were first returned to Earth.

    Researchers can use this technique to measure the ratios of different isotopes in a sample. These ratios serve as a distinctive “fingerprint” that points to the sample’s origin. Thus, two samples with the same isotopic fingerprint likely came from the same source.

    Previous research has shown that oxygen isotopes in lunar samples are nearly identical between Moon and Earth rocks, so Dottin assumed the same would be true for sulfur isotopes. His findings tell a very different story.

    Two distinct isotopic fingerprints

    Dottin and his colleagues specifically analyzed portions of the drive tube sample that appeared to be volcanic rock from the Moon’s mantle. Their analysis revealed that volcanic material in the sample contained sulfur compounds that are very low in sulfur-33, a radioactively stable sulfur isotope. This is very different from sulfur isotope ratios found on Earth.

    “My first thought was, ‘Holy shmolies, that can’t be right,’” Dottin said. “So we went back to make sure we had done everything properly and we had. These are just very surprising results.”

    According to the researchers, the results suggest that the sulfur formed in chemical reactions early on in the Moon’s history, or that it stems from its formation. Experts widely believe the Moon is made of debris ejected from a collision between Earth and a Mars-sized object called Theia. It’s possible that the researchers have found traces of Theia’s sulfur signature in the Moon’s mantle.

    Dottin hopes that as researchers analyze sulfur isotopes from other planets like Mars they may begin to solve this mystery. Isotopic analysis has already provided key insights into how Earth and its only natural satellite came to be, and this approach will continue to help scientists unravel the history of our solar system.

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    Ellyn Lapointe

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