With a camera full of pictures and a journal full of notes, I returned to my European home on Friday after five unforgettable weeks Down Under. My travels ended so the series “Notes from Down Under” will soon come to an end too. This post and the next present a very small selection of the photos I took and report a few of the number of interesting things I experienced.
1. Pinnacles desert, Nambung National Park, Western Australia
About 250 km north of Perth lies a desert scattered with limestone formations. The pinnacles have varying shapes and heights ranging from a few centimeters to 3.5 meters. Their color is yellow or brownish, similar to that of the sand from which they rise. The site is simply stunning and definitely worth visiting.
For the aborigines, however, it is associated with death; they see the pinnacles as fossilized ghosts. One of the many native legends surrounding these structures tells of a group of young boys that entered the desert. Because the place was a women’s sacred site and forbidden to males, the boys were punished by the gods for their wrongdoing. They were buried alive in the desert. Their arms — the pinnacles — rise above the sand as the children reached up to the skies begging for forgiveness before they died.
Fortunately, science tells a less grim story. The pinnacles are sand colored because they are made of lime-rich sands that originated from broken-down sea shells thousands of years ago. Waves and winds brought these sands inland forming dune systems rich in calcium carbonate from the sea shells. Winter rains, slightly acidic, dissolved some of the calcium and carried it down through the sand. Summer droughts resulted in the calcium-rich water being deposited as a cement in the lower levels of the dunes forming a thick layer of soft limestone.
Meanwhile, at the top of the dunes, a layer of soil formed allowing plants to grow. These, in turn, made the soil more acidic which helped the draining process. With more calcium-rich water being carried down, a very thin layer of caliche (a hard deposit of calcium carbonate) formed atop the limestone. Cracks that eventually formed in this hard cap were taken over by plant roots. These carried water from the top of the dunes to the soft limestone layer slowly eroding it. The channels shaped in the bed of limestone by this process were gradually filled with the sand still present above the hard cap. Eventually, these channeled sands hardened forming columns. Finally, bush fires destroyed the top vegetation and winds blew away loose sands leaving only the resilient rock columns.
Some of the details of the formation process are uncertain. The exact role that plant roots had in forming the pinnacles, for example, is subject to controversy. It is also uncertain how long ago the pinnacles formed with estimates ranging from 500,000 to 80,000 years. What is certain is what the pinnacles are: “the eroded remnants of the formerly thick bed of limestone”, as explained on the website of Australia’s Department of Environment and Conservation. So there’s no need to worry about ghosts of naughty aboriginal boys hunting you if you visit the site.
2. Stromatolites, Shark Bay, Western Australia
In the Shark Bay World Heritage Area of the Western Australian coast there are representatives of the oldest life form on Earth. Shark Bay’s stromatolites are only 2,000 or 3,000 years old but they are the modern version of the first living organisms to colonize Earth 3.5 billion years ago, or 3.498 billion years before the first humans appeared.
Stromatolites resemble rocks but they are actually living structures. They are created by cyanobacteria, microscopical organisms related to bacteria but capable of photosynthesis, which organize themselves in colonies and trap sand grains using their sticky surface coatings. These trapped sediments react to the calcium carbonate in sea water to form limestone. The bacteria continue this process year after year forming stacked layers of trapped sand grains and/or limestone, the stromatolites. In a sense, these layered structures are rocks, but they are made up of living organisms.
Fossil records show that stromatolites dominated life on Earth for almost 3 billion years, so the “living fossils” of Shark Bay represent a major stage in the Earth’s evolutionary history. In fact, the stromatolites that inhabited the primitive Earth were essential to the appearance of more complex life forms. The cyanobacteria that make up the stromatolites produce oxygen through photosynthesis. Hence, they were responsible for increasing the level of oxygen of the primitive atmosphere to a level that could support oxygen-breathing life forms. The first fish are thought to have developed about 500 million years ago when the oxygen level was about 20% of all atmospheric gases.
With more complex plants and animals colonizing the oceans, stromatolites became scarce. Today, they can only be found in warm, shallow and salty waters, hostile to other life forms, such as those of Hamelin’s Pool in Shark Bay. For me, one of the most incredible things about this unique place is that you can see Earth’s evolution happening. Not only you can have a glimpse at the way oceans looked like millions of years ago, but you can also see in action the process that allowed the first plants and animals to develop. When the tide is low, you can see little bubbles of oxygen being released from the stromatolites. You can see them “breathe”.