SHARK BAY WORLD HERITAGE AREA

SUNDAY 27.10.2013: We ventured off on our 1.5 km walk down to the reason for this stopover - the stromatolites. On the way there are a number of different points of interest with the first being the shell quarry. Early settlers in the area had few sources of timber or rock for building, but coquina provided a solution. Excavated with a cross cut saw, blocks from this quarry were used to construct many buildings including several homesteads and the church in Denham. Today, shell blocks from this quarry are taken only to maintain historic buildings in Shark Bay. The tiny shells are the remains of the Cardiid Cockle (Fragum eragatum), which have been deposited on this shore over 6,000 years. Small quantities of calcium carbonate within the shells dissolves in rainwater then dries to become a white crystal which binds the shells together. Consolidated shells form a soft limestone called coquina.

"HIGH ON A HILL WAS A LONELY
GOAT..........." (NOT A HERD)!

Distracted - back to the stromatolites! At the entrance of the Hamelin Pool is a massive sand bar called the Faure (Four-ay). Silt, which has been built up over 6,000 years and restricted the tide flow into the pool. The shallow waters of Hamelin Pool evaporate quickly and create super-salty water. In such harsh conditions, few sea snails can survive to graze on cyanobacteria. Hamelin Pool has become a safe neighbourhood for cyanobacteria which build stromatolites of various shapes and sizes at different water depths. In 1954 a group of geologists discovered the stromatolites or "living rocks" of Hamelin Pool which linked life on Earth today, with life on Earth 3.5 billion years ago. The cyanobacteria that built stromatolites appeared when oxygen was scarce. As the original stromatolite colonies expanded, they released more and more oxygen into the atmosphere, eventually raising the oxygen level to 20% of all atmospheric gases. This led the way for air-breathing life forms to evolve. When the tide is in you can see the stromatolite air bubbles.

ERODED STROMATOLITE REMAINS

Raised ridges and rings are the eroded remains. They lived more than 1,000 years ago when the sea level was higher, but died from prolonged exposure when the sea receded.

It is more than 60 years since wagons passed over these stromatolites carrying wool to be loaded onto waiting ships. Deep ruts made by the wheels are still visible in the living stromatolite mats. It can take up to 30 years to grow one centimeter.

Soft black mat - built by cyanobacteria. Those closer to shore tend to be flat and spongy while others in deeper water tend to build up layers to form rocky towers. 

WHEEL RUTS

SOFT BLACK MATS

Stromatolite layers grow outwards, like the growth rings of a tree. The outer layer remains a thin strip of active life with a sticky film to trap and bind drifting shells and sand. Slowly layers are built up which harden into rock. Scientists believe the internal growth rings provide information on local environmental changes during our lifetimes.

"Stromatolites first appeared in a warm, salty sea. Bacteria built the stromatolite empire which dominated the Earth for more than 2 billion years. Without the oxygen that the stromatolites produced, we may not have evolved. Who knows what changes evolution has yet to bring."