One of New Zealand’s most spectacular fossil sites originated 23.2 million years ago. It was formed in a valley dotted with small volcanoes, when rising magma deep below the Earth’s surface came into contact with groundwater. Lava and water don’t mix—they explode. The resulting detonation obliterated the surrounding forest and left a circular, low-rimmed volcanic crater, called a maar, about 3,000 feet across and more than 600 feet deep. The prehistoric rains gradually filled in the hole, forming a lake. Eventually, the subtropical forest grew back, and year after year…
