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GEOLOGICAL TIME Humans evolve 11:59:42 Rocks of the Burren form 11:09 pm The Earth is immensely old - we know from modern dating techniques that it is 4,650 million years old. To put this into perspective, humans evolved only 2 million years ago. By comparison, the rocks of North Clare range between approx. 341 million years and 318 million years old. This is still relatively young in terms of the total age of the Earth! This diagram on the right depicts the age of the Earth as a 12 hour clock. Note how the rocks of the Burren form only at 11.09 pm, and humans appear at only 18 seconds to midnight. This mineral, zircon, contains uranium and is commonly used for dating rocks. 12 11 10 Animals 1 2 No life on Earth 9 3 8 Bacteria and algae 7 Bacteria 4 6 5 Geological time as a 12 hour clock How do geologists date rocks? By measuring extremely small amounts of radioactive elements (e.g. uranium) trapped within minerals in some types of rock. Radioactive elements transform into other elements over time at a constant known rate, so by measuring the amount of what’s left (often only in thousandths or millionths of a gram) we can work out how long ago a particular rock was formed. The oldest rocks in Ireland occur on Inishtrahull, north of Malin Head. They are approx. 1750 - 1780 million years ago. The oldest rocks in the world are found in NW Canada, and they are 4280 million years old. Rocks of Inishtrahull.