(A shorter version was first published on Blogcritics)

The early evolution of life on Earth is a subject I’ve always found fascinating, but it’s a couple of decades since I last revisited the subject in any depth, and having read Oxygen: A Four Billion Year History by Donald E Canfield I now know that pretty well everything I’ve ever read or been taught on the subject was wrong. The idea that gradually algae spread around the earth, pumping out oxygen in a steady-growing stream, well it simply isn’t true.

It’s not surprising my teachers were so wrong, for as I read in Oxygen, a big breakthrough in understanding early life on Earth came in only 1999, when a colleague and friend of the author, James Farquahar, found some highly unexpected results on a study of sulfur isotopes, in Archaen rocks aged from 2.3-2.4 billion years ago. That led to the conclusion that at this time there’d been interaction between UV light and sulfur dioxide gas from volcanoes. Today, that’s absorbed by ozone, of course from oxygen. Further studies on the form some molybdenum takes in rocks of this age from some parts of the world, however, show that in some places there was free oxygen – what’s come to be known as a “whiff” of oxygen.

What was happening was that by around 2.5 billion years ago, the production of oxygen by photosynthesis more or less balanced the consumption of it by volcanic gases. Sometimes the balance shifted one way, so the oxygen disappeared, sometimes the cyanobacteria were beating the volcanoes.

It was between 2.3 and 2.4 billion years ago that “the great oxidation event” (GOE) changed that. Quite what caused it is still up for grabs. Canfield has a favourite, not evolution of cyanobacteria but a less active mantle, as it gradually cooled, cutting the production of reducing gases. Seems entirely plausible to this interested amateur.

But the GOE wasn’t entirely even – it was Canfield suggests concentrated in the atmosphere, the oceans remaining anoxic and rich in sulfide, with more sulfur being weathered from the land through oxidative weathering of sulfides. This is now known as the “Canfield Ocean” – yes after the author, we’re in seriously expert hands here.

Related to that is the likelihood that for much of the Earth’s “middle ages” atmospheric oxygen levels were much lower than today’s. (Any time machine travellers would need to take oxygen cylinders.) The author’s theory is just 10% of today’s levels, others suggest 40-50%.
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Originally published on Blogcritics

How does a hedgehog give birth, given that the babies are born already with spines? The kind of question that mightn’t regularly pop into your head, but certain one that sticks there when you think about it.

The answer is that the babies are born swollen with fluid, so the prickles are beneath the surface of the skin. After birth, the fluid is absorbed and the prickles (which are evolutionarily speaking modified hair) emerge.

That’s one of the many fascinating facts that I learnt from A Prickly Affair: My Life with Hedgehogs by Hugh Warwick, a man who clearly doesn’t only live and breathe hedgehogs, but has certainly spent a lot of wet, cold English nights tracking them around the countryside.

I learnt that their ancestor is thought to have emerged in Asia during the Eocene, although there are ancestors dating back 70 million years, into the dinosaur age. In Britain we have Erinaceus europaeus, the western European hedgehog, although there’s species distributed throughout Eurasia, and down through North Africa.

They’re closely related to shrews and voles, being predominately insectivorous (Hugh watches one consume a large juice slug, having first wiped much of its slime off on a handy road surface – although it still chews a strong tasting leaf afterwards, presumably to cleanse its palate), unlike the American porcupine, which is a rodent. (And of course the Australian echidna, which is a marsupial.)

But this book is far from a collection of facts about hedgehogs. What it is mostly is a exploration of the author’s relationship with hedgehogs, and his meetings with some of the many people obsessed with them. (No wonder they’ve just been voted Britain’s national animal.)

We watch Hugh’s relationship with them and love of them develop as he takes on jobs tracking individuals around the countryside – primarily on projects to see how rescued ones fare when released back into the wild. Against all the rules, he develops, entirely understandably, a personal relationship with his subjects, giving them names and admiring their individual characters. (Although I suspect he’s wrong when he says voles and shrews aren’t similarly complex – look at them in the same detail I think you’d find the same complexity.)

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A shorter version of this post was originally published on Blogcritics

Today I was watching a buzzard soar above the Morvan National Park in Burgundy. Tonight, I’m listening to one owl – maybe more – hooting gently in the valley below me that the raptor was dominating earlier, as the scene is very gently lit by a waxing, but still small, moon. They seem mysterious, unknowable – hard to track their lives and imagine what they would be like, but I’ve got a bit more of an idea after reading Tim Birkhead’s Bird Sense: What It Is Like to Be a Bird.

I know that the raptor has a preponderance of cone cells in its retina (“like low-speed colour film – high-definition and performing best in bright light”), and the owl a majority of rod cells (which “can be thought of as working like old-fashioned high-speed black and white film – capable of detecting low levels of light”). While humans have only one fovea – a spot in the back of the eye where images are sharpest, some birds, including raptors, shrikes, hummingbirds, kingfishers and swallows, have two. So that buzzard’s visual acuity, ability to see fine detail, is roughly twice my own, while I probably didn’t need the science to tell me the owl can see a lot better in the dark than I. (I do sometimes go walking in the forest at night without a torch, but it’s a case of walking by feel rather than sight.)

That might sound quite technical, but really this is a highly readable book, that puts sometimes quite complicated science into terms entirely accessible to any interested lay person. The task of a mallard duck seeking food at the bottom of a muddy pond is likened to a human being given a morning bowl of muesli and milk to which has been added a handful of fine gravel.

“To understand how this is possible, first catch a duck. Then turn it over and open its beak so that you can examine its palate. The most striking feature is a series of grooves radiating around the curved tip, but you need to look beyond these at the outer edge of the bill. What you should be able to see now is a series of tiny holes or pores – some 30 of them. If you look on the lower jaw, you will find even more – about 180. Examining these pores with a magnifying glass, you will see that from each one protrudes the top of a cone-shaped structure called a ‘papilla’, inside which is a cluster of around 20 to 30 microscopic sensory nerve eningds – these are the touch receptors – that connect to the brain.” (p. 78)

Migration is of course one of the great mysteries of bird life, and what stands out from Birkhead’s very clear explanation of the current state of knowledge is just how sketchy and uncertain it is. He begins the chapter with an account of his own work with guillemots on Skomer Island, off the Pembrokeshire coast, getting from new geolocating technology finally, in 2009, after decades of working with them, a detailed understanding of where they go when not nesting on the island. (In short south at the end of July for a few weeks in the Bay of Biscay, before flying 1,500km north to spend most of the winter off northwest Scotland.)
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