Chuck Landis at his home in Otago, New Zealand. He believes New Zealand sank beneath the waves before being re-colonised by drifting species.

Credit: Bill Morris

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Chuck Landis lays a map down on his kitchen table, the cold ocean murmuring just beyond the lawnmower shed. "I just can't believe it hasn't been more questioned," he says. "It's not sound science."

The map on Chuck's table shows what New Zealand might have looked like 30 million years ago, during the Oligocene period. It was lower, with only a few small islands visible.

Long before the mountains were forced up, New Zealand was the dry scalp of a drowned continent. When sea levels rose during the warm Oligocene, most of it was submerged.

The textbook says animals and plants had ridden the land-mass since it broke away from an ancient super continent called Gondwana. The beasts and botany clustered together on the small remaining islands until the sea level fell again. More than just a scientific theory, this idea is woven into New Zealand's national identity: a fragment of an ancient land, a time capsule in the South Pacific - that's the Kiwis.

But Chuck is a scientist - a geologist with a critical eye for such enshrined truths. There is no evidence, he argues, any land at all remained above water during the Oligocene flood. The patches outlined on the map were demarcated because they contain no marine sediments for that period, but there is no conclusive evidence for land-based life either. No fossils, no coal deposits, nothing but hard schist.

The existence of these islands is argued for on the basis of plants and animals - those iconic creatures that adorned New Zealand's classrooms. The moa, flightless for so long evolution stripped it of even a trace of a wing-bone. The lizard-like tuatara, a creature so ancient it pre-dated the dinosaurs. How else could they be here, were it not for the continuous existence of dry-land since the break-up of Gondwana?

"I don't get steamed up about the animals," says Chuck. "And I know it bothers people, but I don't!" He does, however, admit the presence of the large, flightless moa poses a "big problem".

While more than one scientist has suggested the moa's ancestors might have flown to New Zealand and subsequently lost the power of flight, the total absence of a wing-bone in moa skeletons remains a sticking point. However, many now believe the movement of species between land-masses may be far more fluid than we ever imagined.

Chuck is studying the Chatham Islands, a remote collection of rocks 800 km off the East Coast of New Zealand. These islands were totally submerged in the Oligocene, yet support a diverse flora and fauna, most of which is closely related to that of mainland New Zealand. According to Chuck, all of these species arrived by dispersal - riding the waves or prevailing westerlies.

One day, while walking a windswept Chatham Islands coast, Chuck found a willow tree thrashing about in the surf. There are no willows on the Chathams - it had to have floated from the mainland. There is no reason, he argues, a beech tree couldn't have made the same journey; no reason insects, birds, plants and animals couldn't have gone along for the ride.

It only takes one breeding pair, one pregnant female, or one batch of seeds, to start a population. Improbable? Yes, but just because something is unlikely to occur in our lifetime, doesn't make it so in the vast reach of geological time. A lot of 'improbable events' can happen in 30 million years.

The idea of dispersal is not new. In Darwin's day, it was the only way to explain how similar species came to exist on chunks of land divided by wide oceans. Then in the 1960s the world came to accept plate tectonics. Continents breaking apart was an obvious way for plants and animals to become separated, and dispersal was sidelined as an inconvenience, a bit of static against the real science of vicarious distribution. The problem is, it's very difficult to prove dispersal events. While fossil records can give a clear picture of shifting continents and the species that lived on them, plants and animals that simply washed up are much harder to pin down.