Proper Global Heating

I recently came across mention of a new book with a rather OTT title: “Planet on Fire (A manifesto for the Age of Environmental Breakdown)”, by Mathew Lawrence and Laurie Laybourne-Langton. I haven’t read it, but its sales blurb starts with:  

“In the age of environmental breakdown, the political status quo has no answer to the devastating and inequitably distributed consequences of the climate emergency. We urgently need an alternative to bring about the rapid transformation of our social and economic systems. As we rebuild our lives in the wake of Covid-19 and face the challenges of ecological disaster, how can the left win a world fit for life?”

Could it be that the fire is only in the language used here, rather than in the problems the authors believe exist and require urgent remediation?

I can guess what the remainder of the book contains, and I doubt I would be that interested. I’ve long become inured to ‘super-hype’ of the environmental breakdown/catastrophe/chaos variety, but ‘Planet on Fire’ hit a relatively new nerve – one that had only just recently been pinged in the geological part of my forebrain by a relatively recent article in The Conversation. Written by Helen Williams (a reader in geochemistry at Cambridge University), it describes a real planet on fire, the Earth 4.5 billion years ago after it was involved in interplanetary snooker. Hit by a Mars-sized object (Theia), the Earth became molten down to its core – a planet covered in a continuous molten magma ocean a thousand kilometres deep. Now that’s what I would call global heating or a planet on fire!

But how do we know this stuff? It happened so long ago, what is left? The answer is virtually nothing that a geologist can deal with. This seems to me to be similar to the situation with regard to Global Warming where solid “evidence” doesn’t exist, it comes from glorified and intensely complex mathematical models of how the planet’s atmosphere and hydrosphere ought to operate. Four and a half billion year old terrestrial conditions are also inferred from will-o’-the-wisp evidence, because no rocks of that age will ever be found on Earth – the whole crust and mantle were molten, so no rocks existed. Even after crystallisation of the thousand-kilometre-deep melt began, the first crystals to form would have been denser than the remaining melt and so settled through the magma to its floor, never to be seen again. And after the top of the magma ocean congealed, all of those most ancient of surface rocks would have also been lost to us, being subducted into the depths after billions of years of  plate tectonics. The early Earth would have been much hotter than today and so plate-tectonics would have run much faster, relatively quickly devouring rocks of the much smaller micro-continents. The oldest rocks that we know are about 3.7 billion years old, which is more than several hundred million years younger than those inferred first surface rocks.

So, with no surviving rocks as evidence, where do we start? Planetary billiards is inferred from geochemical similarities and differences between Earth and lunar rocks (and meteorites) and aspects of celestial mechanics. Calculations (i.e. mathematical models) of the energetics of such systems suggest accretion of Theia’s core into the Earth and the complete melting of the outer parts of the Earth. But the evidence for the progressive crystallisation of the molten Earth is even more hairy. Some of those deep accumulations of early dense crystals do, however, melt at hotspots, become buoyant, and are carried up to the surface, changing as they rise to form volcanic rocks. These melts bring with them subtle geochemical evidence (usually in the form of unusual isotopic ratios) of the pre-melt existence of those earliest of crystals and thus of those magma oceans.

To conclude, no rocks exist for our study, nor even the first crystals, but just a geochemical taint, a vagueness in very old volcanic rocks. This, and much modelling, is now being used to reconstruct the Earth’s hot-headed adolescence. Isn’t science just wonderful – when it’s done properly?

Diffuse though the evidence for the magma ocean is, to me the Earth’s hot conditions have more credibility for their former existence, than climate science’s “evidence” for catastrophic global warming of a few degrees, 80 years hence. In particular, the reconstructed early history of the Earth-Moon system still fails to fully incorporate all of the evidence available and this is acknowledged, even by Wikipedia. And, like all good scientific endeavours, there is no attempt to sweep away the evidence that does not fit. It is healthy science. Work continues to resolve issues and it looks to an outsider to be vibrant science. What a contrast with the study of climate change, where “the science is settled” and its conclusions are now a consensus, a dogma.  

My interest was piqued by the Conversation article because, when I read geology back in the early 1960s, the evidence for the early phases of the Earth’s history was pure speculation and was summed up in the famous James Hutton 1788 quote that for the Earth “We find no vestige of a beginning – no prospect of an end.” This changed when we brought back lunar rocks and attention turned to assimilating evidence from those ancient rocks, with dates comparable with the inferred periods of a global magma ocean. Geology (or rather geochemistry) is now challenging the claim of no evidence for Earth’s beginnings, and mathematical models are being used to test hypotheses. Meanwhile, on the basis of models, the most extreme of climate activists, like the authors of the “A Planet on Fire” book, are absolutely sure they know how we will end, unless we take drastic measures now.

I was tempted to end by writing ‘vive la différence’, but then realised that this is totally wrong. What I wish for is an honest and vibrant climate science, one that is self-correcting and not overly focused on carbon dioxide. The climate does change and has done so in the past. It should be studied, but without the blanketing pall of future catastrophe.

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via Climate Scepticism

April 23, 2021 at 08:58AM

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