I’ve spent most of the last five years studying rocks formed in the last 10-20 million years. By normal human standards, that’s quite old. If each of those 20 million years was compressed into a single second, we’re still looking at about 8 months’ worth of geological history: by contrast, the average human lifespan would be about a minute, the whole of recorded history would take up the last hour and a half, and anatomically modern humans were almost literally born yesterday (to be precise, just over two days ago).

But now that I’m in South Africa, suddenly 20 million years doesn’t seem very old at all. Johannesburg owes its existence and wealth to the gold bearing rocks of the Witwatersrand Group (some background), which are almost 3 billion – 3 thousand million – years old. That’s 150 times older; going back to our compressed 1 year=1 second timescale, the Witwatersrand is on the verge of celebrating its first centenary and receiving a congratulatory telegram from the Queen, although it still has to defer seniority to the 140 year-old planet which hosts it. From 8 months to 100 years – it seems that one of the guys here was actually being pretty accurate when he sneeringly referred to my New Zealand mudstones as ‘baby rocks’.
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