520,000 crop varieties – and around 250 million seeds – have now been stored in the Svalbard ‘doomsday’ global seed vault. That’s about a third of the approximately 1.5 million unique crop varieties known.

The bunker is designed to keep samples of the world’s seeds safe at –18ºC deep in an Arctic mountain, for backup should a disaster threaten global food production.

The vault’s curator, the Global Crop Diversity Trust, announced the half-a-million landmark yesterday (press release). The total store of crop varieties has doubled in the two years since the seed bank opened.

Nature’s reporter Mike Hopkin helped carry some of the first seeds into the vault when it was first filled: background here (including a podcast).