The question of the age of the Earth and its former inhabitants is one of great interest to us all. Most are aware that the Earth is understood today to be approximately 4.6 billion years in age, but what is the story of the momentous quest – to unravel the mystery of time?
Many early speculations as to the age of the universe abounded in ancient and medieval times. We are all familiar with the literalist understanding of the Old Testament, from which Archbishop Ussher famously calculated a 4004 BC date for the beginnings of the Earth. Yet, this was one of the shortest chronologies in existence: the Babylonians spoke of many hundreds of thousands; the Egyptians of many tens of thousands; and the Hindus many billions of years in their cosmological speculations of the past. However, all these early traditions were not scientific in basis. Rather, they were religious or philosophical and not based upon experimentation and observation. It would not be until after the Renaissance that people started employing scientific methodologies to unravel the mystery.
Various early scholars speculated upon the Earth’s geological history, including Leonardo da Vinci, the universal genius. Leonardo noted that fossils had once been actual living creatures and that the ocean must have once covered the land. As regards the age of the world, however, few people dared to challenge the conventional wisdom based upon the Genesis narrative – one wonders what da Vinci’s own view might have been. However, some scholars did suggest ideas of how to ascertain the Earth’s potential age, such as Edmund Halley. In 1715, he published a paper detailing his idea of estimating the age of lakes and oceans by measuring their rate of salt accumulation, and that this could have implications for the age of the world itself. Though flawed and somewhat crude, such ideas were unprecedented and paved the way for future investigators. However, it was generally not until towards the end of the eighteenth century that the question of the age of the Earth began to be approached in more detail by academics.
Comte de Buffon and Benoit de Maillet were prominent eighteenth-century scientists, who proposed specific ages for the Earth itself. Buffon performed several calculations based upon the idea of a gradually cooling Earth, to ascertain how long might have elapsed since the Earth’s molten state. He eventually settled on a figure of around 75,000 years – young by today’s estimates, perhaps, but a whole order of magnitude greater than those envisioned by most of his contemporaries. Meanwhile, Maillet had been working with the idea that the oceans had slowly evaporated, thus explaining why seashells were found so high above the present sea level – the ocean had simply dropped in height over time due to its loss of water. Though he was mistaken in this idea, his estimate of around two billion years must have been mind-blowing to his contemporaries – imagine hearing the idea that something believed to have taken place six thousand years ago had really taken place billions of years in the past.
At this stage, geology was still not a definite science in itself. However, this would suddenly change. James Hutton wrote his highly important book, A Theory of the Earth in 1795, in which he foreshadowed Sir Charles Lyell’s axiom that “the present is the key to the past” – in other words, current natural forces that we are familiar with should be extrapolated backwards in time, to help us understand how and why the Earth has changed. Much of his inspiration had come from studying strata – the layers of sedimentary deposits that were accumulated in past ages. Most of us are familiar with Siccar Point, the famous location at which Hutton observed an unconformity between layers of strata. Observations such as these caused Hutton to speculate upon an almost endless past, though he did not dare to suggest a specific time dimension to the Earth, other than one shrouded in immensity (often now referred to as ‘deep time’). His views received only moderate attention initially and it was not really until a few decades later that the majority of academics accepted his general ideas.