From ten kilograms of coal, palaeontologists have extracted 241 grains, the smallest just a tenth of a millimetre across. Under UV light they glow blue. And they are 385 million years old – making this find from northwest China the oldest chemically verified amber in the world. The previous record holder, from the late Carboniferous, is 65 million years younger. The team led by Cihang Luo of the Nanjing Institute of Geology and Palaeontology reports the discovery in the journal Science Advances.

Amber is fossilised tree resin, and its invention was a breakthrough for plants: the sticky mass, which hardens in air, seals wounds, guards against fire damage and carries bioactive terpenoids that fight fungi and bacteria. When plants began producing it was an open question – the overwhelming majority of amber finds date from the Cretaceous or later.

First scepticism, then certainty

The grains sat in a coal seam at the Hujiersite site, whose age had already been firmly dated. That something fluoresced there was the first clue; what it was remained unclear at first. "Our first reaction was excitement, followed immediately by caution," Luo told the outlet ScienceAlert. Amber of this age would be extraordinary, so the team initially treated the particles merely as resin-like organic material. Only optical tests, infrared spectroscopy and mass spectrometry established the chemical hallmarks of conifer-type resins.

That raises the question of the producer – and here the find gets provocative. True seed plants, which include the conifers, only emerged around 380 million years ago. The resin is therefore older than they are. According to the researchers, the candidates are progymnosperms, fern-like precursors of the conifers, and tree-like lycopsids. "A non-seed vascular plant was already capable of producing chemically complex terpenoid resin," Luo said.

What did the resin protect against back then? Hardly insect grazing: plant-eating insects only appeared in large numbers in the Carboniferous. More likely it shielded against fire, wounds and pathogens.

Why it matters: the find pushes an important biochemical innovation of land plants substantially further back – into the era when plants were growing taller, developing wood and deeper roots, and reshaping the structure of the continents. Resin production, Luo suspects, may have contributed to that ecological success. And older finds may well be out there: because the grains are so tiny, they may simply have been overlooked until now.