Down to Earth

Year 7 enjoyed a scintillating study of the Earth’s geological history on Wednesday 31 July at the University of Cambridge Sedgwick Museum of Geology. The museum is situated on Downing Street in Cambridge city centre.

Using a huge year-to-view planner, the students placed a number of key events onto the planner, imagining that all 4,500,000,000 years of our amazing planet were squashed into one year.

The very earliest evidence of living things was placed around 21 March, which was cyano-bacteria in stromatolites, found in rocks in Western Australia. The bacteria actually date from around 3,200,000,000 years ago. We were allowed to touch and pass around an actual sample of one of these, from the Museum’s collection.

Evidence of multicellular life has been found dating back to nearly 2,000,000,000 years ago, which corresponds to sometime in early September. This and the stromatolites are the only two significant signs of life for more than the first 2/3 of our Earth’s history!

After that the timeline became much more cluttered as more and more fossils have been found still intact in more recent rocks. We placed five extinction events onto the timeline, three of which were probably mainly caused by the impact of asteroids. On one of these occasions, 96% of the species on Earth in the fossil record ceased to exist!!

Rodrigo impressed everyone, including the curator, by identifying a megalodon tooth as soon as it was pulled out of the collection box – a budding geologist, if ever there was one!

Possibly the most surprising thing we learned was whereabouts human beings have to be placed on the timeline – you have to wait for the last day of the year and then you have to wait for the last hour of the last day; even then, human beings only really arrive in the last 10 minutes of that hour. The last two minutes are as far back as recorded history of human beings goes, all of which helped us to appreciate the sheer enormity of geological time.

Final thought: Don’t expect perfection from geologists … they all have their faults!  (Mr Bennett)

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