Poison on 125,000-Year-Old Stone Points, Oxygen's Carbon Ledger and a Doubly Dangerous Mushroom

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A small scheduling note before we start. In November 1960 the journal Science published a paper by Heinz von Foerster and two colleagues at the University of Illinois. They fitted a curve to two thousand years of human population, followed it forward, and found the number of people reaching infinity on one particular day: Friday the thirteenth of November, 2026. So if it feels a bit crowded this morning, that's why.

This week's issue of the same journal has a more manageable number of people in it, standing beside a lake about 125,000 years ago. The lake was in the Empty Quarter of Saudi Arabia, now one of the driest places on Earth. Back then the climate was in a warm, wet phase, and the basin, called Mundafan, held about 340 square kilometres of fresh water, up to 29 metres deep. There were hippos in it. Around it were buffalo, camels, gazelles and ostriches.

A team led by Chris Clarkson of Griffith University in Australia, with Saudi Arabia's Heritage Commission and King Abdullah University of Science and Technology, surveyed a stretch of that old shoreline and collected more than five and a half thousand stone tools, lying among the animal bones.

Then the team looked at what was still stuck to the stone. Several points carried traces of animal tissue near the tip, and resin and plant fibre at the base. That's what you'd expect from a stone tip glued and bound onto a shaft, a weapon assembled from parts. And on several points, chemical analysis found compounds matching Acokanthera schimperi, known as the arrow-poison tree. It makes toxins that stop the heart.

Until now, the oldest chemical evidence of a poisoned weapon was about 60,000 years old, from a rock shelter in South Africa. This would more than double that. The paper's title says poisoned hunting weapons outright. The team's own residue specialist, Carney Matheson, is gentler: the traces, he says, raise the possibility. A residue shows that the plant touched the stone. It can't say what the person holding it had in mind.

If it was poison, consider what that takes. You have to know which tree, and how to prepare it. You have to trust that a small wound will do the work, if you're prepared to follow the animal until it does. That's chemistry and patience, a very long time ago, in a place often drawn as a corridor that early humans hurried through on their way out of Africa. These people had settled in.

From an old lake to the air above it. About half the carbon dioxide we emit from fossil fuels doesn't stay in the atmosphere. The ocean and the land take it up. How much goes where is hard to measure, because nobody can put a meter on a forest or a sea.

Ralph Keeling's group at the Scripps Institution of Oceanography has been coming at it sideways since 1989, by measuring oxygen. Burning fuel uses oxygen up. When plants on land absorb carbon dioxide, they give oxygen back. When the ocean absorbs carbon dioxide, it mostly dissolves, and no oxygen changes hands. So oxygen works as a second set of books. Compare how much has gone missing with how much carbon dioxide has piled up, and you can split the bill between land and sea.

Eric Morgan and colleagues have now run those books across three decades of flasks of air. From 1990 to 2019 the ocean took up about 35 percent of fossil emissions, and its uptake kept growing. The land's net take, meaning what plants and soils absorb minus what's released when land is cleared, was about 13 percent, swinging from decade to decade with no upward trend.

That second number is the uncomfortable one. Many climate models assume that extra carbon dioxide fertilises plants, so the land soaks up more as emissions rise. The air doesn't show it. Morgan's word for the land sink is fragile, and the models used to plan emissions cuts are counting on it.

Further out, the James Webb Space Telescope has been looking at Beta Pictoris, a young star 63 light years away, ringed by a disc of dust and rubble where planets are still forming. Astronomers report in Science that they've found two ices in that dust: frozen carbon dioxide, and water ice of a particular kind, called amorphous. Its molecules are frozen in a jumble instead of a tidy crystal. Ice only stays that way if it has never been warmed. So this ice probably formed in the cold between the stars, before Beta Pictoris existed, and has stayed frozen ever since.

And in Florida, on mossy palm trunks in the wetlands, there's a brown mushroom about the size of a thumbnail called Galerina indica. Writing in Current Biology, Andrew Kunik and colleagues report that it is the first mushroom known to make both psilocybin, the compound in magic mushrooms, and amatoxins, the poisons in the death cap. In principle, a trip and a poisoning in the same mouthful. The genes for the psilocybin seem to have jumped in from another species entirely. Florida's state mycologist says it's hard to tell from its neighbours, even for an expert, which is one more reason to leave little brown mushrooms alone.

As for the infinite population, the count this morning is a bit over eight billion. Plenty, but finite. See you tomorrow.