I recently posted a quick blog on my recent very brief trip to Broome, on the far north-west coast line of Western Australia.
Broome is famous for its pearling industry and its tourist resort at Cable Beach where the climate is usually beautiful in the Australian winter, with lovely sunsets and the camel rides along the beach.
For astronomers, it boasts almost no light pollution and 300 clear nights a year – and in Winter (eg. June), those clear nights are not too cold, and there are not too many nasty mosquitoes around then either, so it makes for awesome star gazing indeed.
For most people though it is a place to refuel and re-charge before heading back into the deserts or up north-east into the tropical regions of the Kimberleys.
What few are aware of though is that within 2000km of Broome, there are a range of geologically fascinating regions which offer rather unique insights into how our world developed and how life evolved.
One of the reasons that there is so much geologic remnants for most of the geologic ages in this region is that it has been relatively undisturbed by disruptive geologic events, particularly in the last 450 million years.
So let’s take a bit of a geologic journey to help understand our world a little better.
If one heads 1,800km south to Shark Bay near Canarvon, one can see living Stromatolites – rock-like structures along the coast which are actually slowly formed by a multitude of layers made up of limestone created by microbial mats of “blue-green algae” or properly known as cyanobacterium. This is one of the few places in the world where these are still growing and these microbes have an enormous significance to the evolution of life and climate on earth.
At Marble Bar which is regarded as the hottest place in Australia and is near Port Hedland and the iron ore mines, and some 700km south of Broome, one can find the earliest fossils of living creatures in the world – yes, there are fossils 3,500 million years old consisting of remnants of Stromatolites and these blue green algae.
Why are these “algae” so important to the evolution of the earth?
The earth formed some 4,500 million years ago as asteroids of iron, ice, dry ice, methane, ammonia, etc collided and formed an ever larger body, while the heat from the collision formed the molten core of what was to become earth, and what is still responsible for volcanic activity today. Eventually the outer crust of the new earth cooled sufficiently to allow the steam to fall back as rain and create some oceans which had high levels of dissolved metals, particularly iron, and high levels of sulphur and carbon dioxide, but little oxygen.
Further bombardment of asteroids and comets to around 3,800 million years ago (the “Late Heavy Bombardment”), appear to have contributed the water to make up around half of the ocean’s water that we have today.
There was no ozone layer to protect any newly evolving life forms from the intense UV radiation, so it appears the 1st life forms to evolve were sulphur-dependent, anaerobic (not using oxygen), bacteria which evolved at the depths of the oceans protected from the UV radiation.
The next life forms to evolve were the “blue-green algae” or cyanobacteria which were amongst the first photosynthetic bacteria, and these were to bloom and dominate the oceans for some 2000 million years, forming these Stromatolites, and in the process consuming carbon dioxide and releasing free oxygen.
With each cycle of blooming, the released free oxygen oxidised the dissolved metals nearby in the ocean such that ferrous iron was converted to insoluble ferric oxide which was deposited in layers in the sediment.
These layers of iron oxide deposits can be seen in the banded sandstone of the Bungle Bungles in Purnululu NP some 900km east of Broome.
And of course, this cyanobacterium oxygenation of the oceans, is what created the massive iron ore deposits which are being mined in the Pilbara regions of Australia near Port Hedland.
2,400 million years ago, this culminated in the Great Oxygenation Event (GEO), as the levels of dissolved metals in the oceans had been exhausted, and the oxygen was now free to escape to the atmosphere and to also form the important ozone layer.
The build up of oxygen was associated with fall in carbon dioxide and methane in the atmosphere creating a “reverse-greenhouse gas” scenario which cooled the earth dramatically and to the extent that earth became a giant snow ball by 700 million years ago.
Release of greenhouse gases from volcanic activity resulted in a thawing of earth and by 630 million years ago, set the stage for the evolution of Ediacaran fauna (named after the Ediacara Hills of South Australia),- fossils of which can also be found in the Broome region. Hence ended the reign of the blue green algae as now they not only had a “toxic” ocean full of oxygen, but now they also had animal predators to contend with.
Around 550 million years ago, the Halls Creek fault system formed which caused folding of the King Leopold Range to the NE of Broome, this area had been created by volcanic activity resulting from tectonic plate movement around 1,900 million years ago, and Cambrian fauna evolved (mainly trilobites from 540 million years ago and onwards).
450 million years ago a giant Devonian coral reef formed on the three sides of the King Leopold Range and coincided with the evolution of fish.
300 million years ago, sea levels fell with a new ice age of the Permian period, burying the coral reefs, forming limestone which later became exposed with uplift of the plate resulting in the Limestone Ranges and their beautiful gorges and waterfalls in Western kimberleys, 400km east and NE of Broome.
250 million years ago, it is thought a Near Earth Object (NEO) such as a asteroid or comet, wiped out most life forms, ushering in the Triassic and Jurassic period of mammals and dinosaurs. One of the candidate impact sites for this event is the Bedout High underwater crater NW of Broome.
The Broome sandstones contain fossils and footprints of dinosaurs from these times. To protect these sites, they are not accessible by the public, apart from the most well known, 3-toed dinosaur footprints on the rocks on the coast of Broome which can only be seen at low tide on a Spring Tide.
300,000 yrs ago, a large meteor caused the Wolfe Creek Meteorite Crater some 800km east of Broome and is the 2nd most obvious crater in the world after Barringer Crater in Arizona.
A fascinating region indeed.
What does this teach us?
Species do become extinct, and often quite rapidly – either from climate change, new predators, or catastrophic events such as impact from asteroids.
More than 50% of our atmospheric oxygen is created by oceanic photosynthetic organisms (phytoplankton) – and perhaps their reduction in numbers by 40% since 1950 due to acidification and warming of the oceans is a potential for concern.
To an alien, the human race could well be seen as a plague on earth, rapidly using up the resources it and most other life forms need, and replacing it with toxic chemicals which not only deplete the ozone layer but threaten global warming and potentially catastrophic climate change such that we may end up like the blue green algae – suddenly finding ourselves in a toxic environment of our own creation with resources consumed, without a food supply, without oil, without fresh clean water, and facing new predators (eg. antibiotic-resistant microbes, new viruses) to take us down.
Apparently 95% of the peoples in India are already colonised by super-bugs resistant to almost all the antibiotics currently available, while global travel has the ability to spread pandemics far quicker than ever before – although the Black Death / Bubonic Plague did make a good effort of knocking us off – it only reduced the population by 30%, no where near enough to prevent the population explosion of the past 50 years.
It is estimated 30% of species will be extinct by 2030 and 50% by 2100.
hmmm… no point worrying about all this though because not enough people really care enough to stop it from happening, and there is no point worrying about things you cannot change.
