Planet Earth - The Immensity of Geological Time: Charles Lyell & Mount Etna

In the early 19th century, the scale of time in geological history was unknown.    The first hint that the Earth is very old came from a volcano.

Charles Lyell visited Mount Etna in 1828. 




Mount Etna is the largest active volcano in Europe. It covers a huge area (38 x 47 km) and has a maximum height of nearly 3.5 km. 


(The painting of Etna is by Edward Lear)

The volcano dominates the landscape of North-eastern Sicily, Italy.   

Lyell saw that it was made of many lava flows, piled one on another.  This suggested it had existed for a very long time.    


He calculated - from the size of the volcano, and from local evidence of the rate of production of lava over time - that it must be many tens of thousands of years old.



(The photo shows layered lava flows on Etna)

He knew from the work of William Smith that the percentage of extinct fossil species in a rock was an indicator of the rock’s age. 

For example, if 50% of the fossils were of extinct species, it was of moderate age.

But when he found a limestone layer that ran beneath the oldest lava, he found that 95% of the fossils represented living species. 


With so many modern types of fossil in the rocks under Etna, in geological terms Etna must be very young.  Yet in human terms, it appeared ancient.

Lyell had discovered that human time and geological time were not  comparable. He now realised that the Earth must be immensely old in human terms.


Lyell's "Principles of Geology" is a classic of 19th century science.





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