Mammals Doomed - in 250 Million Years

THIS ARTICLE, based on THIS ACADEMIC PAPER, suggests that in 250 million years a new supercontinent - Pangea Ultima - will form and as a consequence of this CO₂

in the atmosphere will rise. The resulting temperature rise will be sufficient to make mammalian life impossible. There might be hope for burrowing nocturnal rodents living near the poles. (The diagrams indicate that the UK might be a good place if you are a burrowing nocturnal rodent.)

The authors (the main one is Bristol based) provide lots of data and discussion, particularly about why CO₂ should rise. Read it for yourself and see if you agree.

Whether there will be humans around in 250 million years to observe mammalian doom is doubtful. I think we will be long gone by then, seen off by evolution or our stupidity. But, being human, we live to speculate.

The habitable Earth in 250 million years - maybe.

 Down to Earth Extra October 2023

The October 2023 edition of Down to Earth Extra has been published. You can download it HERE or you can read it below.

 It Happened 8 Thousand Years Ago...

About 8 thousand years ago things got a lot cooler - 3.3°C cooler. It got cooler because the surface waters of the North Atlantic became fresher - and less heavy.

Because they are less dense they cannot sink. If they don't sink warmer waters cannot come northwards to replace them. And so northern Europe suffers from a cold Atlantic and temperatures drop. And you get a drought. The technical term for this is "a perturbation of the Atlantic Meridional Overturning Circulation (AMOC)".

The cause, 8 thousand years ago, is thought to be the draining of Lake Agassiz in central Canada. Measurements made in the Ythan estuary just north of Aberdeen show sea level rising 2.4 m at 13mm per year around 8.5 thousand years ago.

Worryingly, the same thing is happening now, but with a different cause. The Greenland is cap is melting. It rained on the top of the ice cap (3.2km in elevation) in 2021 for the first time ever!

At first sight the fall in temperature because of global warming might seem to be a good thing. But I doubt it. Adding chaos to chaos is seldom beneficial.

Read all about this in THIS ARTICLE.

Was the PETM Linked to Hydrothermal Venting? 

The PETM (Palaeocene-Eocene Thermal Maximum) was a period of rapid global warming. Sea surface temperatures rose 6°C within 10 to 20 thousand years. This rate of temperature rise is not very different to what is happening currently. As THIS ARTICLE says, the temperature rise led to the release of organic carbon into the atmosphere. Expressed as CO₂, 0.24 gigatons (Gt) per year. Currently we release 0.51Gt per year. The article is based on THIS PDF.

In the PETM the temperature rise led to the most dramatic biologic changes since the asteroid killed the dinosaurs.

What was the cause? At the time there was magmatic activity around the area which was to become the Atlantic. This was the start of continental rifting. Much of the activity was the intrusion of sills. Could the sills have led to the release of methane from organic rich sediments?

The article suggests that is what happened. Using a 3-D seismic survey they found pockmarks beneath the P-E boundary. Detailed study suggests they formed from hydrothermal venting. 

Because they happened in shallow water the CH₄ went straight into the atmosphere. (At depth it would have been mitigated by the methane being oxidised to carbon dioxide.)

Three-dimensional view of seismic reflection data off western Norway. The greytone lower part is a vertical ‘slice’. The coloured part shows the depth variation of sediments that fill hydrothermal vent systems beneath a horizontal unconformity. (Credit: Berndt et al, Fig 1b)

 Early Life and Stromatolites

I came across THIS PODCAST from GEOLOGY BITES and thought it was very interesting and very approachable. It concerns recent discoveries which prove (probably) that early stromatolites (3.48 Ga) are of organic origin. No one questions the organic origin of current and more recent stromatolites, but these ones are very old!

To get the most from the podcast scroll down THIS PAGE to see the astonishing photos.

I have a slight personal interest in this as we used the interviewee's guide book when we were in Marble Bar, Western Australia in 2013.

And here is my photo of some stromatolitic limestone from the area

 Do Plants Evolve Continuously Or In a Big Bang?

In THIS ARTICLE the authors (many of whom are based in Bristol) explore the hypothesis that, like animals, plants have a higher capacity for innovation early on but later, not so much. The article is based on THIS PAPER in Nature. 

To do this they collected 548 traits of 400 living and fossil plants and plotted the 130,000 observations onto, what they call, a design space. Also on this design space, they plot the predicted traits of extinct shared ancestors.

Then it gets complicated - at least for me - and they produce diagrams such as the one below which have axes which I find difficult to contemplate. I think I know what they mean, but don't ask me to explain it! The Nature article excels in producing even more challenging diagrams. I am sure there is a logical explanation of what NMDS1 and NMDS2 is but I do not know what it is.

Correction - NMDS is "non-metric multidimensional scaling".

The two axes summarise the variation in anatomical design among plants. Coloured dots represent living groups while the black dots represent extinct groups known only from fossils. The lines connecting these groupings represent the evolutionary relationships among living and fossil groups, plus their ancestors, inferred from evolutionary modelling. (The chlorophytes and charophytes are marine and freshwater plants while the remaining groups are land plants. Angiosperms are flowering plants). Philip Donoghue et al / Nature Plants

The result of all this impressive data gathering and analysis is that plants have evolved continuously and not in an early "big bang". And the Animal Kingdom is no different.