It ain't half wet, Mum

I have been rather engaged in writing for publication, so here to prove that, like Granny Weatherwax, I aten't dead yet, here's a sampler about a little-known event that I came across while in NZ.

*

Into every life cycle, a little catastrophe must fall, and in the Carnian stage of the late Triassic, the geological record shows what seems like a long monsoon. That, at least is what the evidence suggests, but ‘long’ is a weak descriptor for a wet spell that went on for a million years, or maybe two. At the end of the downpour that was the Carnian pluvial episode (CPE), the lepidosaurs (the ancestors of the modern-day snakes and lizards) were present, and so were the mammaliaforms (the ancestors of the mammals). The heavy rains had triggered some major changes.

Quite a few invertebrates went missing at this time from among the ammonoids, bryozoa and crinoids, so what caused this changeover? At that time, there was just one continent, Pangaea, and the sea was probably hotter than it is now, so there would have been enough water in the atmosphere to feed continual torrential rain. To make things worse, there were huge volcanic outpourings at this time, generating the flood basalts of western North America.

Basalt flows, Snake River, Washington state, USA.

That sort of volcanic activity makes things warmer, and it also injects lots of water vapour into the atmosphere, and also lots of CO₂. This would have fed global warming, again raising atmospheric water levels, and down came the rain, in the Carnian Stage, a subdivision of the lowermost Upper Triassic period. On 10 November 1987 Alastair Ruffell and Michael Simms linked a stripe of grey in the red stone of Somerset’s Lipe Hill to Simms’s research on crinoid extinction in the mid-Carnian.

This period was about 234 to 232 million years ago, and aside from wiping out some branches of life and opening the way to others, the CPE left a number of traces in the rocks. These include clay deposits in sedimentary basins, pollen traces that reflect vegetation that thrives in humid conditions, lots of amber, and many changes in the isotope balances.

The oxygen isotope ratios (¹⁸O:¹⁶O) alter, suggesting global warming of 3 to 4°C during the CPE (though this could also point to a change in seawater salinity). The carbon-13 levels rose and fell in parallel with higher levels of sedimentation (which points to higher rainfall).

In other words, the world may survive massive changes in the climate, but can humans manage to cling on? That is probably a key question for the generations after mine, and also my generation, if we have a descendant-based interest in the future.