We’re sitting here in the Yarra in Studley Park and you can see some rocks behind the river there on the cliff, and those rocks are actually deposited in an ocean about 400 million years ago. Today they’re part of Australia and people are jogging past them. But 400 million years ago we were maybe under two or three kilometres of water and those layered rocks were laid down over periods of hundreds to thousands of years. And after that long period of time when they were in an ocean, they became involved in a collision when these rocks were attached to the eastern edge of Australia to form what is now Melbourne.
Victoria shows some great examples of how Earth’s geological processes work, and one of the philosophies that geologist use to try and understand the rocks we see preserved in the rock record is that the present is the key to the past.
So by looking at the rocks that are forming today and the environments in which they form, we can make inferences about how rocks that we find preserved in the rock record might have formed. So if we find a rock that’s 400 million years old and it looks very similar to a modern rock, it’s reasonable to infer that the same processes we observe today directly were responsible for forming those rocks all that time ago.
Now a cool thing about geology is that you can also use the past, even the long distant past, as a key to the future. You can go back, look at these old rocks, try and understand how they’re formed and then make predictions about what may happen in the future.
And in Victoria an example of that is we’ve got many small volcanoes in western Victoria that have erupted over a period of millions to thousands of years and we can date these rocks radio-metrically and we’ve established that one of the youngest volcanoes is really only about four or five thousand years old. And we can also establish that the average time frame between the eruptions of these volcanoes is about four or five thousand years, so that means that it’s likely that another volcano will erupt sometime in the future in Victoria and we don’t know exactly when; it could be in ten years or a hundred years or maybe even a thousand years but one day some farmer is going to look into his back paddock and there’s going to be something exciting growing for him to see.