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I realise that it might just be a turn of phrase, but I am quite concerned about the use of "unlimited" with respect to tapping magma chambers as a source of energy. It may be an unimaginable amount, but it isn't unlimited. Ask anyone who has been in space and seen the finite size of …

Your article got me thinking about indirect contributors to the Mediterranean diet's healthful properties ( 13 January, p 32 ). Specifically, with large amounts of fresh and unprocessed foods, how many more beneficial microorganisms are supported? We are learning of the importance of our intestinal microbiome: has anyone yet compared that of long-lived Mediterraneans with …

It seems that the Mediterranean diet as described manages to minimise added sugars. No desserts, no sugary breakfast cereals, no sweets or cakes or pastries. And no fruit smoothies, sugary soft drinks or sugary, ultra-processed food. I assume sugary treats are allowed on occasional celebration days. Could this be the simple reason why the diet …

Common descriptions of a healthy Mediterranean diet don't reflect typical diets in much of the region today. For example, a reliance on whole grains better matches German and Danish diets. What's more, deaths from cardiovascular disease don't support an obvious correlation with better health . Portugal, Italy, Greece and Cyprus all have higher rates than …

You report the supposed 5 per cent chance that artificial intelligence will make us extinct, according to a survey of AI experts. Asking only such people about the consequences of AI is analogous to asking only Manhattan Project scientists about the consequences of developing atom bombs ( 13 January, p 16 ). Predicting the broader …

From Letters, 13 January

Tony Green suggests that, billions of years from now, only the mega-rich will be able to afford to decamp to the moons of the gas giants to avoid the sun's expansion, while the rest of us plebs are left behind. I think he is taking too pessimistic a view about the survival of economic systems …

We appreciate your efforts to present diverse views concerning the definition and application of the Anthropocene. Nevertheless, we are concerned by the closing quote of the article, which suggests that standing against defining an Anthropocene Series/Epoch in the geological time scale, as we do, is to deny anthropogenic global climate change. As scientists and as …

When it comes to dark skies, Aotearoa (New Zealand) aims to be the world's first dark sky nation , a fact that warrants a mention. It is a lofty goal, but the country already has five dark sky reserves to enjoy while we wait for this to happen ( 6 January, p 28 ).

When archaeologists are confronted with observations for which they have no clear explanation, they often tend to attribute religious, or symbolic, significance, as with the straight roads between settlements found in the Ecuadorian Amazon. Might it not be that for some mundane, technical reason, such as a mode of transport, the roads needed to be …