Shark Bay and ancient Earth

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Shark Bay and ancient Earth


This is a transcript of a QuickTime movie (19.3 MB) recorded at Shark Bay in 2005. Adrian Brown, from the Australian Centre for Astrobiology, talks about Shark Bay and its relevance to ancient Earth.

Transcript:

I think here in Shark Bay we really do have a unique opportunity to study what the early earth might have looked like in the form of these stromatolites and these microbial pools, ah sorry microbial mats. I think that geologists really gain a lot by looking at modern environments to try and then go back as a comparison point to the ancient environments that they are looking at preserved in the rocks and this can be, this link is important between, for example, stromatolites we see here at Shark Bay and the stromatolites we see in the Pilbara. Let me give you three examples of things that have been carried out here, things that have been observed here, that can be applied in the Pilbara. For example, the stromatolites here. Some of them have lithofied or made into rock, the top of their surface, and some scientists have suggested that this may be just to shield them from the sun because we only see it in the ones exposed on the surface. So if we go and look for that sort of feature in the field in the Pilbara and find it, then we can learn a bit more information about those stromatolites. Perhaps they too were exposed to the sun, perhaps they were just shallow tide effected stromatolites like the ones you see here on the beaches at Shark Bay. So that's one example of something we can see in the Shark Bay stromatolites and we can carry across to look for in the Pilbara.

Another example is the way that we have different microbes living together to form these stromatolite communities. We have the stromatolites forming mats themselves, we have also these flat lying microbial mats. We also have them lapping up onto each other and crossing each other and living together as a community. This sort of idea was really only gained by geologists by going to places such as Shark Bay. That opened their eyes to the idea that many different types of microbes might form different shapes that we see in the stromatolite rock in the Pilbara. So they can go, they can look for not only the stromatolite forms, the conical shapes and the domical shapes, and all the different forms that stromatolites might take. But they also look on the size to see if they can see any evidence of the microbial mats that they see at Shark Bay. So that's the second example of ideas that we can pick up by looking at the modern environment.

And then we can also look at some of the ways in which the stromatolites form and also some of the ways that ripple marks can come into being. Ripple marks can be preserved very close by the shallows, the stromatolites and the shallows that we see here at Shark Bay. So if we have a ripple mark that means that we have very shallow lapping water and waves that means that we don't have a really deep ocean that the stromatolites are living in. So we can go and look in the rocks at Pilbara for stromatolites that have right next to them, wave shapes and we can look for ripples and we can suggest, well these stromatolites lie very close to these ripples here and we can say that was probably a good indication that the stromatolites were formed in a shallow marine environment, not the deep ocean and not on land. So by recognising these features that's the way that we can learn more about the environment in which the rocks formed and of course this being the example of ripple marks is quite famously being used by the Mars Exploration Rover Team. They found ripple marks in the rocks where Opportunity the rover landed and they were able to tell from that, that that environment had lapping shallow water. So geologists look for these sort of features in a contemporary, modern day environment, so that they can learn, get some more ideas for the things that they should actually be looking for in the really old rocks and that way they use this modern day environment as a map or a dictionary to try and interrogate the rocks and to learn more about the rocks that we see at 3.5 billion years ago or ancient times such as the rocks we see in the Pilbara.

Contents


Introduction

Context

Early Life

Evidence

Acknowledgements

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