The Ash That Held a Telescope: Western Australia's Bungle Bungle Range

From a distance, the Bungle Bungle Range looks like a row of giant beehives painted in orange and black stripes. Up close, those stripes are not rock layers at all—they are the fossilised work of microbes that once lived on the surface of the sand, binding grains together with sticky films of organic matter. The 350-million-year-old Devonian sandstone of Purnululu National Park records a moment when life first began to shape the land.

The Sand That Remembers

The Bungle Bungle Range sits in the remote Kimberley region of Western Australia, a plateau of quartz sandstone deposited during the Devonian period, when much of the continent lay under shallow seas. The sand came from an ancient mountain range to the north, now eroded to nothing. What remains is a 300-metre-thick sequence of cross-bedded sandstone, tilted slightly eastward by later earth movements.

What makes Purnululu extraordinary is not the sandstone itself, but what happened to its surface. After the rock was uplifted and exposed, colonies of cyanobacteria—single-celled organisms that photosynthesise—grew on the outer face of the domes. Their dark organic coatings protected the sandstone beneath from weathering, while the uncolonised orange bands weathered more quickly. The result is a landscape of alternating dark and light stripes that track the contours of ancient sand dunes.

A Cathedral of Domes

Erosion carved the plateau into a maze of towers, gorges, and sheer-sided domes that rise up to 250 metres above the surrounding plain. The domes are arranged in parallel ridges, following the joints and fractures that ran through the original sand body. Water did the carving: seasonal floods, flash storms, and the slow creep of groundwater over tens of millions of years.

The range is named for the Aboriginal English term "bundle bundle," referring to the grass that grows on the surrounding plains. The traditional owners, the Kija people, have lived in the shadow of these domes for at least 20,000 years. Their rock art and burial sites are scattered through the gorges, some painted on the very sandstone surfaces the cyanobacteria protect.

The Stripes That Tell Time

Each black stripe is a living microbial mat, no more than a few millimetres thick, that has been growing and dying in place for thousands of years. The orange bands are bare sandstone where iron oxide—rust—stains the grains red. The contrast is not just visual; it is a record of how life and rock interact.

The domes of Purnululu are one of the few places on Earth where the boundary between biology and geology is still visible on the surface.

During the wet season, the cyanobacteria become active, drinking moisture from the humid air and cementing loose sand grains with a glue of polysaccharides. During the dry season, they desiccate and darken, forming a crust that sheds water. The process is slow, but over millions of years it has sculpted a landscape that looks artificial—too regular, too striped, too deliberate.

What the Domes Conceal

Beneath the striped crust, the sandstone contains fossils of the Devonian reef that once surrounded the range. Crinoid stems, brachiopod shells, and fragments of tabulate coral are preserved in the rock, remnants of a warm sea that covered the Kimberley 350 million years ago. The same sea built the Napier Range to the north, whose limestone gorges hold a different chapter of the same story.

But Purnululu's most important fossils are invisible to the naked eye. The cyanobacteria themselves leave no bodies, only traces: the organic films they deposited, the grains they bound, the surfaces they shielded. Those traces are a fossilised ecosystem, a record of Earth's first land-living communities.

The Slow Work of Microbes

The Bungle Bungle domes are still growing. Each wet season adds another microscopic layer to the microbial crust. Each dry season hardens it. The process is so slow that a human lifetime produces no visible change. Yet over geological time, these tiny organisms have done what wind and water alone could not: they have turned a flat sandstone plateau into a city of domes.

In a continent famous for its ancient landscapes, Purnululu is one of the oldest still being shaped by living things. The microbes that built it are not fossils—they are still there, working in the rain, darkening the rock, holding the sand together.