Cooloola (Great Sandy National Park)

Just north of Noosa, the coast has been building itself out of sand for hundreds of thousands of years, and it built in order. Wind and sea threw up dune behind dune: the youngest sand nearest today’s beach, older ridges marching inland, the oldest set right back perhaps seven or eight hundred thousand years. Everything else barely changes. Same quartz sand, same rainfall, same mild coastal air. The only thing that varies as you walk inland is time.

Stop and let that settle, because it is one of the quiet wonders of Australian science. Walk from the beach toward the hinterland and you walk forward through several hundred thousand years of soil development, reading the whole life story of a soil in a single afternoon. Anywhere else, ageing a soil means guessing across sites that differ in a dozen ways at once. Here the dunes hold the other variables still and let time alone do the talking, which is why researchers keep arriving from the far side of the world to read the field ridge by ridge like a manuscript. Each grain of sand is a buried clock: a quartz grain stops recording light the moment the wind flips it into the dark of the growing dune, and in the laboratory that stored dose reads back as a date. Cooloola has been dated grain by grain, back the best part of a million years.

So take the walk. On the young grey sand behind the beach the soil is barely a soil, thinly organic, still carrying the trace of phosphorus the sand arrived with, and the plants match it. Low pioneers, a scrub of she-oak and banksia, all of it on the way up. Walk on, onto dunes a hundred and forty thousand years old — the biggest ridges in the whole field, and nowhere near the oldest — and the country does something that startles anyone who expected poverty to mean bareness. It grows tall. On these middle-aged sands stands the densest, highest forest of the whole sequence, tall blackbutt and bloodwood, real timber on bottomless sand. Knowing nothing of what came before or after, you would call this the best country of the lot.

Then keep walking, and watch the forest begin, almost imperceptibly, to come down. The giants thin and shorten; the canopy opens. You are walking down the far side of the arc now, into what ecologists call retrogression, the soil’s long wind-down as the last reachable phosphorus leaches below the roots and does not come back. On the oldest dunes the forest has given out altogether. Their bleached podzols plunge more than twenty metres, deep enough to reach the journal Nature in 1981. Measured ridge by ridge, the topsoil gives up something like nine-tenths of its phosphorus between the first dune and the last. What stands on the most ancient dunes is not forest but low, wiry, hard-leaved heath: the wallum.

In spring it out-flowers the rainforest on the range behind it. The two arcs have crossed. The mass of the vegetation peaked back on the middle-aged dunes and has fallen away to almost nothing, while its variety has climbed, dune by dune, to its maximum here on the hungriest sand of all. In one walk you have watched a soil, and the forest riding on it, born, grow up, grow rich, grow old, and run down at last to a low, brilliant, threadbare heath.

That is the wonder of Cooloola, and the irony cuts. A stretch of country that looks like worthless scrub, and was twice fought over by sand miners who could see nothing in it but the heavy minerals buried in the dunes, turns out to be one of the most scientifically precious landscapes in the country: a clean, million-year experiment that no laboratory could ever build.

A practical word. You reach much of Cooloola only by four-wheel-drive on sand tracks that strand the unwary on a rising tide, and no phone signal carries across a good deal of it. Check conditions and closures with QPWS, and check the ground in front of you. The country rewards the reading; it does not forgive the careless.