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We know that large language model chatbots can't be trusted to always tell us the truth. We now find that it is hard to get them to "unlearn" concepts and facts without retraining on "cleaned" data, a wholly impractical task ( 4 November, p 40 ). One wonders what the next problem could be. I …

Previous research I was involved in showed that aerosol sprays don't linger, as James Wong found with water sprayed on plants. I don't spray my water-loving plants and haven't done for years. A stack of Maranta , moth orchids, Nepenthes and Venus flytraps are kept damp with regular light watering at a north facing window …

I loved Alice Klein's piece about South Australia's transition to renewables. I would say it had a bit of unexpected help. South Australia formerly had a major automotive industry. Holden, once Australia's largest car-maker, ran a huge factory in the Adelaide suburb of Elizabeth. From 2013, it started ramping down production, finally shutting in 2017. …

For the solution to puzzle #243 ( 21 October, p 47 ), fewer than 31 customers at a time means there won't be a clash.

When considering the origin of life on Earth, note that it all runs on the same power system of ion gradients across a membrane. As this is universal, it must date back to a universal common ancestor ( 4 November, p 36 ). How could such a system have developed on early Earth with only …

There was no mention of the admittedly unfashionable panspermia proposal, the idea that life came from beyond Earth. While it doesn't explain the origin of life, it could, if true, mean that the first organisms didn't come into being here, but in a different environment. In this hypothesis, life on Earth began not when the …

The concept of quantised space-time may be the key to understanding the multiverse – and the requirement that the plethora of universes must display a wide range of properties that fortuitously result in a limited number being relatively stable and life-friendly ( 28 October, p 30 ). If the fundamental constituents of space-time were to …

Your article about chimpanzees seeking higher ground for tactical reasons reminds me of one of our cats. He would run upstairs for a better look if he saw something interesting in the back garden. What was curious was that not only did he have the nous to do this, he also had the orientation sense …

You published a timely article about preserving us from the possibility of being wiped out by Martian microbes brought back to Earth in study samples. I hope sufficient steps are being taken to prevent Earth microbes from contaminating Mars and elsewhere that we visit ( 4 November, p 21 ). It would be a tragedy …

Further to Bryn Glover's call for names for the opening chapter of the proposed next geological epoch – the human-induced Anthropocene – I would suggest that an appropriate title for its first age might be "The End" ( Letters, 4 November ).