Guest essay by Don EasterbrookA crater in northern Siberia, spotted by a passing helicopter, has received worldwide attention and continues to be a top news story. Since then, two more mysterious holes have been discovered elsewhere in the region. Now the new holes, smaller in diameter but similar in shape – are posing a fresh challenge for Russian scientists, according to the The Siberian Times. Theories range from meteorites to an explosion of methane due to global warming.Figure 1. Yamal ‘mystery crater.’ (Siberian Times)Anna Kurchatova of the Sub-Arctic Scientific Research Centre said the crater was formed by a mixture of...