Scientists studying Kilauea Volcano have found that it is coughing up material 4.5 billion years old — roughly the age of the planet, meaning volcanoes serve as master recyclers.

Although Earth’s mantle — the part between the inner core and the outer crust — is solid, it nevertheless circulates at a glacial pace. And over many millions of years, it completes the cycle, scientists say.

Some geologists had speculated that this process would have eliminated any chemical signatures from Earth’s infancy.

But a research paper published Friday in the journal Science shatters that notion.

“We found geochemical signatures that must have been created nearly 4.5 billion years ago,” said Andrea Mundl, a postdoctoral researcher in geology at the University of Maryland and the lead author of the study, in a statement accompanying the announcement of the findings. “It was especially exciting to find these anomalies in such young rocks. We don’t yet know how these signatures survived for so long, but we have some ideas.”

The Maryland researchers looked at rocks that erupted in the last half-century from Kilauea Volcano and Savai’i Volcano in Samoa.

The surprising geochemical “fingerprints” were found in the ratios of the isotopes of tungsten and helium.

Isotopes, chemical cousins, differ in the number of neutrons. Some isotopes decay at a specific rate, so can serve as a sort of geological clock.

Whereas tungsten-184 has existed since the solar system formed, tungsten-182 results from the decay of hafnium-182, which happened fast — during the first 50 million years of Earth’s formation, an eye blink in geological time.

Most rocks have a similar ratio of tungsten-182 to tungsten-184 — but those that have an especially low or high level of tungsten-182 offer clues to their creation.

“Nearly all of these anomalies formed within the first 50 million years after the solar system formed,” Mundl said. “Higher than normal levels of tungsten-182 are seen in very old rocks that most likely contained a lot of hafnium long ago. But lower levels of tungsten-182 are rare, and resemble what we might expect to see deep beneath the surface, in or near the planet’s metallic core.”

The rocks from Hawaii and Samoa indeed had an unexpectedly low level of tungsten-182.

But they also showed an unusual ratio of helium isotopes, the scientists found.

Helium-3 is extremely rare on Earth, and tends to show up in samples of rock that have not been melted or otherwise recycled since the planet first formed. Helium-4, on the other hand, can form from the radioactive decay of uranium.

A higher-than-normal ratio of helium-3 to helium-4 typically signals ancient rocks that have not changed significantly since the planet formed.

“Variations in the isotopic composition of helium have been long known but have never been correlated with other geochemical parameters,” said Richard Walker, chairman of the University of Maryland Department of Geology and a co-author of the paper. “Rocks with high helium-3 to helium-4 ratios have commonly been speculated to contain ‘primitive’ mantle material, but how primitive was not known. Our tungsten data show that it is very primitive indeed, with the source region most likely forming within the first 50 million years of solar system history.”

The researchers speculate that the volcanoes might be drawing material from Earth’s core, where the ratios are expected to favor low tungsten-182 and high helium-3.

Alternatively, the rocky outer surface of Earth might have formed in sections, with magma oceans in between. Parts of these magma oceans might have crystallized and sunk to the bottom of the mantle, preserving the ancient tungsten and helium signatures.