Earth’s core carbon may be isotopically heavy, Hawaiian lava droplets suggest

Melt droplets trapped in crystals from Kīlauea’s lavas carry carbon at about −1‰ on the carbon-13 scale, against −7‰ for ordinary Hawaiian mantle, and a PNAS team reads that gap as carbon leaking out of Earth’s core.

Peer reviewed · Measurements of volcanic samples · Core origin is an interpretation

Researchers led by Yves Moussallam of Columbia University’s Lamont-Doherty Earth Observatory say they have estimated, for the first time from real samples, the carbon isotope makeup of Earth’s core. Writing in PNAS, the 11-member team reports that tiny droplets of magma from Hawaiian volcanoes carry unusually heavy carbon. They argue it came up from the core, and that it points to carbon-rich meteorites from the outer solar system as the main source of Earth’s carbon. The catch: the core is never sampled directly, so every step from the lava to the core is an inference.

Evidence at a glance

Is this a big deal?

It is a promising first step, not a settled answer. Nobody had put a measured number on the core’s carbon isotopes before, so even an indirect estimate is new. But it rests on one volcanic system and an interpretation of where its magma came from. Treat it as a strong hypothesis that other hotspots now need to test.

What scientists found

Carbon comes in two stable forms. About 98.9% is carbon-12 and about 1.07% is carbon-13, roughly 1 atom in 93, according to NIST. Geochemists report small shifts in that ratio as δ¹³C, in parts per thousand (‰) relative to a reference standard. A higher number means “heavier” carbon, with a little more carbon-13.

The team found two distinct values. Droplets from shield-stage lavas, the main volcano-building phase that Kīlauea is in today according to the USGS, converge on −1 ± 2‰. Droplets from rejuvenated-stage lavas, a late, low-output phase that comes after a volcano drifts off the hotspot, sit at −7 ± 2‰, which the authors call a normal mantle signature. Even at the edges of the reported ranges, the two groups do not overlap.

A 6‰ gap sounds tiny, and in atom terms it is. Starting from NIST’s natural abundance, it works out to about 6 extra carbon-13 atoms in every 100,000 carbon atoms. The size is small; the consistency between the two groups is what carries the result.

How they found it

Nobody can drill to the core, so it cannot be sampled. The team instead looked for carbon that might have escaped from it. Hawaiʻi is fed by a mantle plume, a column of hot rock that the authors infer is rooted in the thermal boundary layer just above the core.

Their samples were melt inclusions: droplets of molten rock sealed inside crystals as the crystals grew. Rising magma loses carbon dioxide as gas, much like a soda going flat once opened (the comparison covers the escaping gas, not the chemistry). Inclusions trapped before most of that gas escaped keep a better record of the original carbon, which is why the team chose them.

According to the Yale release, the samples included droplets from the Keanakākoʻi eruptions between 1500 and 1840 and the 1959 Kīlauea Iki eruption. The team then compared the shield-stage results, thought to tap the plume’s axis, with rejuvenated-stage droplets, thought to come from ordinary mantle dragged in at its edges.

“We interpret this as carbon leaking from the core,” Damanveer Grewal, a Yale assistant professor who led the analysis of where the carbon came from, said in the release.

Why it matters to you

This changes nothing about daily life, volcanic hazards or climate this year. It speaks to a question of origins: where the carbon on Earth, including the carbon in every living thing, ultimately came from. The study’s answer is that much of it may have arrived in meteorites from the cold outer solar system, not from the rock that formed close to the Sun.

The meteorite connection

The authors write that their results point to carbon-13-rich carbonaceous chondrites as the primary source of Earth’s carbon. These are carbon-rich stony meteorites that formed far from the Sun. According to the Yale release, the core’s carbon is too heavy to have come from the carbon-poor inner solar system material that built most of Earth.

Timing matters too. Grewal argues in the release that such material could have joined the core permanently only during the final stage of Earth’s main assembly. Had it arrived earlier, much of it would have been sent back into space during later collisions; had it arrived later, the core would already have been closed off. That timing argument is the team’s interpretation, not a separate measurement.

What the evidence does not show

• No core sample. The core value is inferred from lava, through an assumed plume structure. “This is the first observational estimate of the isotopic composition of carbon in Earth’s core,” Grewal said; the key word is estimate.
• One hotspot. All of the reported values come from the Hawaiian plume. Other deep plumes have not yet been tested this way.
• Other explanations exist. A 2023 study of basalts from Lōʻihi Seamount, also fed by the Hawaiian plume, framed the open question in its title: primordial or recycled carbon? Recycled carbon, carried down from the surface by sinking plates, is the alternative that title names.
• Uncertainty is wide. Each value carries ± 2‰, a third of the gap between the groups.
• We have not read the full paper. Sample counts, instruments and the authors’ treatment of alternatives are in the full text, which our tools could not open. This article relies on the abstract and the release.

How this fits what we already knew

The abstract describes the core as the planet’s largest carbon reservoir. Its isotopic makeup was, in the authors’ words, “long presumed to be beyond observation.” Earlier studies of Hawaiian plume carbon, such as the 2023 Lōʻihi work, had already asked whether it is primordial or recycled. This study adds a specific number for the plume’s axis and a specific explanation.

SciQuest covered a different window on the deep Earth this week: lab measurements of how hot iron melts under core-like pressure. That study was an experiment; this one is a measurement of natural rock plus an interpretation. Our guide to Earth’s layers explains where the core–mantle boundary sits.

Outside views

SciQuest has not yet obtained comment from an independent geochemist, and the coverage we found quotes no outside researcher. We will add one if we receive it.

How other headlines framed it

• Yale News led with the origin story, core carbon that may have come from the far reaches of the solar system, and kept the “may”.
• Phys.org republished the Yale release with the same framing.
• The paper’s own title makes the narrower claim, isotopically heavy carbon in the core, and its abstract uses “interpret” and “point to”.

What happens next

In SciQuest’s view, the natural test is other hotspots thought to rise from the deep mantle: if their axis magmas show the same heavy carbon, the core explanation gains ground. The Yale release also says the work may help clarify the role of core carbon during episodes of intense volcanic activity, an idea the abstract does not test.

In one sentence

Magma droplets from Kīlauea carry carbon about 6‰ heavier than ordinary mantle, and the team behind the measurement argues it is core carbon delivered by outer solar system meteorites, an interpretation that other hotspots will need to confirm.

Read next

• Iron melts at 4,160 K under core-like pressure: the lab side of studying the core.
• Where did Earth’s water come from? The same meteorite question, asked about water.
• Mauna Loa facts: Kīlauea’s giant neighbour on the same plume.

Sources and disclosure

1. Moussallam Y, Grewal DS, Georgeais G, Lee H, Rose-Koga EF, Lerner A, Holman B, Wallace PJ, Gauer Pasqualon N, Anderson OE, Jackson MG. “Isotopically heavy carbon in the core.” Proceedings of the National Academy of Sciences 123(46), published online 9 November 2026. doi:10.1073/pnas.2610912123. Abstract read via Crossref.
2. Shelton J. “Earth’s ‘core carbon’ may have come from the far reaches of the solar system.” Yale News, 9 November 2026 (source of the Grewal quotes, sample eruptions and timing argument).
3. USGS Hawaiian Volcano Observatory. Geology and history of Kīlauea and Evolution of Hawaiian volcanoes (shield and rejuvenated stages).
4. NIST Physical Measurement Laboratory. Atomic weights and isotopic compositions: carbon (carbon-12 0.9893, carbon-13 0.0107).
5. Graham DW, Michael PJ, Truong TB. “Carbon isotope composition of basalts from Loihi Seamount: Primordial or recycled carbon in the Hawaiian mantle plume?” Earth and Planetary Science Letters 617, 118248 (2023). doi:10.1016/j.epsl.2023.118248.
6. Republication read for framing: Phys.org, 10 November 2026.

Disclosure: This article was drafted with AI assistance and checked against the sources above; the full PNAS text could not be accessed, so details beyond the abstract and the Yale release are not reported. Calculations by SciQuest: carbon-13 is 1.07% of natural carbon (about 1 atom in 93); a 6‰ rise in the carbon-13 to carbon-12 ratio lifts the carbon-13 share from 1.0700% to about 1.0764%, about 6 more atoms per 100,000. The graphic is a SciQuest original built from the abstract’s values. Spotted an error? See our corrections policy.