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Microbial Changes of Decomposition

When someone dies, their microbiome goes through predictable changes as decomposition commences, according to the University of Colorado, Boulder's Jessica Metcalf and her colleagues.

Through a combination of microbial community characterization, community-level metabolic reconstruction, and analyses of soil biogeochemistry, she and her colleagues examined what happens to the microbial community when mouse and human corpses decompose, as they reported in Science last week.

"There's this complete overhaul of the living community in the surrounding area," Metcalf tells The Atlantic's Ed Yong.

But each time, the same species appear in the same order at more or less the same time, and, Yong notes, that order doesn't appear to change with soil type or seasons. And it's the same for mice and humans.

This suggests that these microbial changes could be used as a forensic tool to gauge when someone might've died. Currently, co-author David Carter, an associate professor of forensic science at Chaminade University of Honolulu, tells Newsweek that the team can pinpoint time of death to within two days for a body that's been decomposing for 25 days.

"For this to be relevant for forensic science, we needed to show that this microbial clock really exists in an outdoor scenario, where you have scavengers, insects, and daily temperature fluctuations," Metcalf tells Yong.

Newsweek also notes that being able to present such forensic evidence in court will take time, as it would have to go through a Kelly-Frye hearing to establish its admissibility before having to convince a jury of its merits. Carter also says that the effect of additional variables — like whether the victim was on antibiotics or was an alcoholic — need to be teased out.