Rocks are the shifting skin of the Earth, and allow us an insight into our own place in the world.
Exploring stone with word, image, and art puts humanity into context with eternity.
Earth solidified from a ball of gas around 4.54 billion years ago, and Western Australia is one of the few places on the planet where fragments of the Archaean Earth have survived. The landscape is unimaginably old and has undergone spectacular transformations across billions of years. The surface we walk today is just a flicker in the unraveling of time and space.
Margaret River, where I live in the far south-west, seems young in comparison. The oldest granite of the Leeuwin Complex is just one billion years old. It is found in a narrow band of granite-gneiss that runs along the coast between Cape Leeuwin and Cape Naturaliste.
A grain of zircon crystal from the Jack Hills in the Murchison district is the oldest known fragment of Earth’s crust, formed a whopping 4.4 billion years ago. And scientists now suspect that rocks underlying the nearby Pilbara region are 4.3 billion years old, 800 million years older than previously thought. The Pilbara also lays claim to the oldest evidence of life on land, with micro bacteria preserved in chert from hot-springs that flowed 3.48 billion years ago.
The granites were created by multiple magma events between 1000 and 520 million years ago, when the continents of east Antarctica, and then India, collided with Australia. When India drifted away again over 100 million years ago, the Leeuwin complex was torn away from the edge of the continent.
The Margaret River granites have been weathering away for aeons. Mixed in with shell fragments in sand on the beaches are grains of hornblende, quartz, zircon, garnet, mica, feldspar and ilmenite, all worn from veins in the rock.
Then, only one million years ago, the ancient outcrops were capped with a much younger stone. A cycle of ice ages had begun, when prevailing winds from across the Indian Ocean blew carbonate sand into lines of sand dunes. These were then cemented by rain into the soft Tamala limestone so characteristic of the south coast of Western Australia.
The fragile limestone is weathered into fantastic shapes. There are caves deep within the earth, dripping with calcite formations. Outcrops along the coast preserve the shapes of plant roots that first stabilised the dunes thousands of years ago. And then there is surface weathering, where the softer pockets of stone are washed away, leaving strange and beautiful stone sculptures.
Tamala limestone also preserves the climate history of the last million years, as the great Pleistocene ice ages peaked and retreated. It is still forming today, a process which can be witnessed amongst the coastal sand dunes that fringe the sea. The limestone mirrors the time frame of human emergence, and projects forward, into the Anthropocene.
Look closely at shapes in the granite, and you might see how it flowed as a liquid. Watch as grains of crystal washed from veins in the rock draw patterns in the sand with each passing wave. Approach a water-carved boulder from just the right angle, and you might see a face in it. Or pause by a limestone cliff, and listen for the sound of soft stone resounding with the song of the sea. Rocks have many tales to tell, and their weatherings give rise to the story of all life in the landscape.
Copyright Jinni Wilson 2021