As we work our way back through extinction-cycles, before Chicxulub wasn't P/T - but T/J. P/T gets the press; to solve that mystery, we should get better data on later events (so better-preserved). Tonight let's look at the Triassic's closing bracket.
Triassic's last good epoch is called "Rhaetian". The post T/J epoch is called "Hettangian"; the Jurassic-proper gets going in the next epoch the "Sinemurian".
Bas van de Schootbrugge at Utrecht University is pointing to mercury (Hg) in Hettangian plants (Copenhagen, Aarhus, and Tianjin are also represented; but ScienceDaily pointed me to Utrecht). Northern Germany was then a coastal lagoon. It was full of... ferns, sucking up the carbon-dioxide of which the Hettangian had much. We read that ferns are a colonising plant, like conifers; they take root first in disturbed and mildly toxic soil. I suppose they always were; when vascular plants first took to the land, the soil there wasn't much better than it was under the Proterozoic (yaaayyy lichens).
First up, the T/J Hettangian rocked this planet back to the Proterozoic - again. Even the conifers weren't doing well. Of especial interest to the researchers is that the ferns were mutated. Something was trying to kill them too and it certainly wasn't CO2. That something was the Mad Hatter.
The paper pins the toxic Hettangian to a ~1.2My span, in which they fit four pulses of quicksilver enrichment with a fifth after that (+1.62My?). The pulses match the 405ky eccentricity-cycle (thereby itself verified for the late Triassic). The paper notes that the isotopes of new mercury taper out such that they waver over counting the expected fifth pulse in the Hettangian (they'd extend the bad times to 2My!). It concludes that these pulses, therefore, are simply pulses of atmospheric intake, not additional spewings of poison.
The initial dose must have injected a megayear's supply of horror into Triassic air. It is certainly volcanic.
So yeah: let's not use mercury in low-orbit plz.
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