Rock Gallery

Glacial dropstone

Glacial dropstone. Rounded and facetted by being dragged over bedrock beneath a glacier for thousands of years, this boulder finally fell to the bed of a central Australian sea corridor about 720 million years ago where the river of ice reached the shoreline and began to break up into floating icebergs. Much of Australia was entombed in ice sheets at this time, and the prolonged glaciation partly accounts for the flatness of the modern continent. East of the MacDonnell Ranges, Northern Territory, Australia

© Reg Morrison/AUSCAPE All rights reserved

Zircon crystals found at Mount Narryer, Western Australia

Zircon crystals found at Mount Narryer, Western Australia. Dated by the decay of their uranium content as being older than 4.1 billion years these are among the oldest fragments of Earthly material ever found. Australia alone has material of this age and it all comes from a thin strip of primordial crust (the Western Gneiss Terrain) that runs down beside the western edge of Western Australia from Mount Narryer, to beyond Greenbushes in the south-west corner of the State. The crystals are glowing here with bands of polarised light that display the onion-like layering of the silica that forms them. The circular depression near the middle of the crystal at top centre is a pit formed by ionised particles fired at the dust-sized zircon crystal during the dating process. (A crystal recently extracted from the Western Gneiss Terrain at nearby Jack Hills has yielded a date of almost 4.4 billion years.). Australian National University, Canberra, Australia

© Reg Morrison/AUSCAPE All rights reserved

Glacial debris, dropstone in Precambrian tillite, about 750 million years old

Glacial debris, dropstone in Precambrian tillite, about 750 million years old. Rounded and facetted by being dragged over bedrock beneath a river of ice for thousands of years, this boulder finally fell on to the bed of a central Australian sea corridor about 720 million years ago where the glacier reached the shoreline and began to break up into floating icebergs. Much of Australia was entombed in ice sheets at this time, and the prolonged glaciation that occurred is part of the reason for the flatness of the modern continent. Bronco Bore, East MacDonnell Ranges, Northern Territory, Australia

© Reg Morrison/AUSCAPE All rights reserved