Night and Day - Driver of Diversity!

I have come across a couple of articles which are promoting the idea that daily changes in the oxygen content of shallow shelf seas in the Cambrian were a major driver of the diversification of animal life in the "Cambrian Explosion". You can read about it HERE and HERE. The inspiration for both articles is THIS PAPER in Nature.

The main point of the paper is that in shallow shelf seas the amount of oxygen in the water would change, depending on the amount of sunlight. During the day, photosynthesis would increase the amount of oxygen in the water. But at night the decay of organic matter on the sea bed would reduce the amount of dissolved oxygen. This rejoices in the term ""benthic diel oxygen variability". Diel was a new word for me and means "involving a 24 hour period". Whether days were 24 hours long in the Cambrian is a rabbit hole we will not go down!

An animal in such a shelf sea would have to cope with wildly varying oxygen content in the water in which it lived. Those that survived would do so by becoming more diverse - or so the authors believe.

At this boundary, the temporal extent of potentially global glaciations of the Cryogenian (blue vertical fields) is depicted as well as this study’s region of interest (ROI). 

A The sandy shelf area in Laurentia and its increase in extent over the Neoproterozoic-Palaeozoic, from ref. 14 (black line, grey field represent bootstrap resampled error at ±1 std. dev.). 

B One modelled global average surface air temperature representation (at low latitude) modified from ref. 34, see also supplementary information and Supplementary Fig. 1 for comparison with clumped isotope data from ref. 27. Grey field represent ±1 std. dev and +25 °C marking a transition from cold (blue) and warm (red) climate states. A gradual shift from an icehouse to a greenhouse climate (blue-red colour). 

C The divergence of animal clades (one of several possible time-calibrated trees, based on ref. 96, with approximate divergence between lineages based on ref. 97 and ref. 71). Boxes represent early branching clades and Bilateria that today perform cellular oxygen sensing mechanisms with the Hypoxia-Inducible Factor (HIF) system (filled orange) or not (grey), based on refs. 43,53. The positions of Ctenophora and Placozoa are based on ref. 96.

 Down to Earth Extra April 2025

The April 2025 edition of Down to Earth Extra has been published. You can download it HERE or you can read it below.

 Strange Fossil Preservation

If you are fossil hunting, one place you would not bother with is a pyroclastic flow. But THIS ARTICLE describes the finding of a wonderfully preserved griffon vulture in volcanic rocks not far from Rome. This was in 1889. A distinguished geologist (not the finder) identified the bird and noted that he preservation was unusual. And then it was forgotten about.

Then, more recently, the remaining specimens were re-examined and found to be extremely well preserved. The head and neck were CT scanned and the creatures eyelids, tongue and skin texture were seen in great detail.

Studies were extended to the birds feathers and they also were exquisitely preserved down to the finest structures. And the feathers had been replaced by zeolite!

So now palaeontologists have a new rock type to search!

 

 How to Analyse Past Atmospheres

I came across THIS ARTICLE and found it very interesting. It describes methods used to extract and analyse gases trapped in rocks and minerals. The gases are in  various salts, quartz and crystallized magmas.

The technique used sounds simple - crush the rock and collect the gas. But it has to be done in a vacuum-sealed press and send the released gas to a mass spectrometer for analysis. The gas does not all come out at once but in pulses as different parts of the sample fail. Repeat and repeat until you have enough gas. The crushers are very small - 10 grams of rock is considered "an insane quantity"!

Crush Archaean rocks and with care you can get a sample of Archaean air. Its age can be proved by radiometric dating of the included noble gas isotopes. There have been some surprises - higher oxygen levels appearing earlier than expected.

But read the article to get an introduction to this fascinating subject.

 Is There Helium in the Core?

A correspondent sent me THIS LINK which seems to link three opposites. Helium is a very light noble gas which does not mix with anything, iron is a metal and the earths core is hot, pressurised and a long way away. But there are hints that all is not as one assumes!

The rare (at the Earths surface) form of helium is He-3 (2 protons, one neutron) is found during volcanic eruptions. Where did it come from? Is it left over from the Big Bang? 

In normal circumstances you can find a few parts per million of helium in iron. The experimenters decided to look at conditions similar to those of the Earth' core. For this they used a laser heated diamond anvil cell. And found that they could get 3.3% helium into iron.

If this is what actually happens in the core it has implications for what happened as the Earth formed. And it may mean that the helium from volcanic action came from the core and not from, as yet unfound, reservoirs. What I find mind boggling is the scaling up from tiny experimental quantities to the Earth's core!