From Graham Brooker, Sydney, Australia
The article on how some alien worlds may lack the conditions for the discovery of fire suggests that smelting ores to extract metals is probably a prerequisite for the evolution of advanced societies. Yet it neglects the possibility of enzyme or catalyst-mediated manufacturing. For example, one of the hardest and longest-lasting materials in nature is dental enamel, and that only requires a temperature of 35°C (95°F) or less to produce. So, maybe there is hope for civilisations without fire (26 August, p 17).
