ONE NIGHT LATE in 2017, I knelt on a coral cay on the Great Barrier Reef, watching a green turtle lay eggs. It was 2 am. The moon was high, the sea flickered silver. A few gulls and black noddies called from casuarina trees; otherwise, the beach was quiet.

The turtle sat in a bowl of sand, tilted beetle-like on a gentle angle. I knelt a few centimetres behind her rear flippers. From here I could see her impressive dark shell, flecked with sand, and the top of her leathery head. Switching my torch on, I directed a shaft of light into the egg chamber she had dug. It was a marvellous thing: deep, round and perfectly smooth inside, like a well.