Are folks at the University of Bristol intentionally trying to annoy me? In the very same week that I write about the abundant signs of old age in the rock record, they put out a press release which states:
By the end of the 19th century, many geologists still believed the age of the Earth to be a few thousand years old, as indicated by the Bible, while others considered it to be around 100 million years old, in line with calculations made by Lord Kelvin, the most prestigious physicist of his day.
The press release is advertising a talk by Cherry Lewis, who has authored a biography of radiometric dating pioneer Arthur Holmes, so this statement is presumably intended to emphasise the importance of his contribution to establishing the age of the Earth. However, the part in bold is, quite simply, wrong. It might be an accurate statement of the situation at the end of the 18th century (in as much as geology actually existed as a discrete discipline back then), although even that post-dates James Hutton proposing a world which had “no vestige of a beginning – and no prospect of an end”. But by the late 1800s pretty much every geologist worth his salt had recognised that the stuff above the rocks – glacial, beach and flood plain deposits – represented at least a few thousand years, and that the rocks themselves represented a vastly longer timespan – not thousands, but millions of years.
The question at the end of the 19th century was how many millions? Tens? Hundreds? Thousands? On one side of the debate – the young side – you had Lord Kelvin’s estimate, based on the thermodynamics of the Earth cooling from an originally molten state, of between 20 and 100 million years. For many geologists, however, even 100 million years was a rather compressed span of time in which to fit the story told by the rock record, particularly the numerous cycles of diversification and extinction recorded by fossils. Geologists’ attempts to estimate an accurate age from the rock record itself concentrated on calculating how long it would have taken the ocean to accumulate its present concentration of mineral salts, or on compiling geological columns and working out how long it took the sediments within them to accumulate. Unsurprisingly, given the number of unknowns involved in such calculations (and, in the latter case, the impossibility of compiling a global geological column anyway), the spread of estimates was quite wide; at the lower end were ages compatible with Kelvin’s estimates, but numbers an order of magnitude higher were also being thrown into the mix.
This was where the discovery of radioactive decay, and its application to dating, made its invaluable contribution. It didn’t force geologists to contemplate the fact that the earth was millions of years old – other evidence had already convincingly established that – it was that it provided an accurate method of counting those millions. Think of it this way: if you’re living in London and a friend arrives at your door having driven down from Edinburgh, you would know, just from your knowledge of geography and the speed that cars can travel at, that the journey must have taken considerably longer than five minutes; even without the aid of a watch to provide an exact journey time, you’d know that it would have taken a few hours.
Historical accuracy aside, my real worry with a statement as wrong as this is that the claim that ages of millions of years are based solely on radiometric dating is a common young-earth creationist canard, hoisted just before they attempt to prove that “carbon dating” is flawed. We really shouldn’t make things easier for them by ignoring the achievements of 18th and 19th century geologists in disestablishing the scientific authority of the Bible. I did browse Cherry Lewis’s book – The Dating Game* – once a few years ago, and from what I can recall it explained the science reasonably well; I do hope that she didn’t get the history quite as wrong as this press release does.
*which, as you can probably guess, is far from the only – or the most popular – book with that title available from Amazon.