It's life Jim, but not as we know it!

Occasionally, just occasionally we get to see some really cool stuff in our wanderings in the shubbery. Well, OK cool stuff if you are into rocks and geo stuff. In 2006 I got to see a site that is considered worthy of the equivalent of heritage listing at a location generally known as North Pole (in the Pilbara).

A bit warmer than that other joint, it is also home to some outcropping sedimentary beds that are dated by lots of careful science (you need volcanic rocks to date, so you carefully map out the rocks in the area and decide which ones brackets the age of the sedimentary rocks you are looking at, then figure it out that way). Anyway, I digress. These rocks are bloody old, somewhere in the order of 3.5 billion years (3,500,000,000) ans they have this wavey dome like structures in them.

3,500,000,000 year old stromatolites in the Pilbara

While a few like to seek other explanations, the majority of people who see this accept that this is the earliest evidence for life on earth, which had probably not been solid for a full 1 billion years yet. The life form is generally known as stromatolites, and WA is also home to a couple of extremely rare examples of living stromatolite locations, most famously Shark Bay near Denham, and less well known but closer to civilisation in Lake Clifton, just south of Dawesville between Bunbury and Mandurah. I have also had the opportunity to visit both of these locations as well. Now, these domes are made up of particles of sand and silt trapped in algal like mats, or cyanobacteria, which are filament like stringy things naturally matted together like felt. They look for all intensive purposes like rocks, or black coral like bombies, but are in fact soft like felt, and can be easily sliced with a knife (as was demonstrated on a student field trip).

Shark Bay Stromaltolites

Soft enough to cut with a knife (and less, we did put it back afterwards).

You can see the layers and the gentle wavey domes.

Lake Clifton Thrombolites - Living fossils!

These thrombolites are just next door to a winery that I noticed was suffering from the loss of trade now the new Mandurah bypass road is up and running. Easy to get to for a quick visit then of for a tasting (and cheap wine).

I have also seen more recent outcrops of fossil stromatolites from different parts of the state, and have a small example of it sitting on the shelf in my office, but this one is probably only 450 million years old or there abouts.

What so cool about these things? Well, in the begining, we had a massive "greenhouse gas" problem. So much CO2, that literally there was no oxygen for us to exist on. This is evident by the nature of various sediments of the time. Some minerals that normally oxidise in the presence of air as we know it today can be seen rounded by abraision... litterally plucked from the rock they formed in, and rolled around in water in a stream similar to pebbles we like to use inlandscaping these days, and then deposited into a pile of other sediments and re-cemented to protect it from oxidation.

Anyway, back to no oxygen. Along come these cyanobacteria, and in the presence of sunlight we get that marvelous process called photosynthesis occuring, producing sugars and oxygen, both of which we now rely on to exist today.

It took a little while to get going... but about 2.6 billion years the cyanobacteria got plentiful enough to make heaps of oxygen, permant changing the makeup of our little 3rd rock from the sun. In fact, youmight say they almost did themselves out of a job, except plenty of other forms of life evolved to utilise this stored energy and convert it all back to CO2.

One final connection to where I am now.... once all this oxygen was freely available, iron which used to be quite soluable in water started to convert into rust coloured scum, like Perth bore water and become insluble in water. This happened as the water mixed (storms or algal blooms or something) and tiny layers of iron started being put down in the sediments with the usual stuff, givig rise to the funniest of all rock types.... BIF's (Banded Iron Formations). These have now become the source of much of our iron ore industry that has made WA a source of a lot of the world's steel.