Geophysics traces the Nullarbor's faint surface trenches to caves collapsing upward

A void opens in limestone at depth, out of sight. The rock above it fractures and settles into the space, and that disturbance migrates upward through the overlying layers over millions of years until the surface itself sags ^[13]. The features barely register on foot, and they show up clearly in a modern digital landscape model ^[8]. Take "a few metres" as five and a 20-kilometre trench has a length-to-depth ratio of about 4,000 to 1 ^[22].

The setting helps: the plain covers more than 200,000 square kilometres of limestone, left behind when a shallow sea retreated about 14 million years ago ^[1][2]. Victorian-era colonial explorers described it as "the sort of place one gets into in bad dreams" ^[3]. The Mirning People of the Nullarbor and the Great Australian Bight have lived on this southern margin for tens of thousands of years, through the sea-level fall and rise that came with the buildup and collapse of the last ice age about 20,000 years ago ^[4].

The authors write that their work "provides a new way to identify hidden caves elsewhere", and that this holds "even beyond our own planet" ^[14]. The Earth-side version of that claim stands on its own data. The off-planet extension is an inference the account states in a single sentence, and the reason the Nullarbor version works is local: the caves there are known and accessible where they breach the surface ^[6]. That access is what let boreholes and in-cave measurements calibrate what the elevation data was showing ^[11]. They also say the results "will change how scientists interpret cave landscapes globally" ^[20].

The stakes on Earth are unglamorous and large. Karst covers 15% of the ice-free land surface and supplies water to between 10% and 25% of the global population ^[16]. The upper end of that water figure is about 1.7 times the land share; the lower end is about two-thirds of it ^[17].

Caves are sheltered from surface weathering and erosion, so they hold snapshots of ancient environments and ecosystems that are gone above ground ^[18]. They may also hold life that evolved and adapted in isolation, among the least studied organisms on Earth ^[19]. "To learn more, we must first locate the cave structures," the authors write ^[23].