William Smith, a surveyor who built canals in England during the late 1700s, used these ammonite fossils to prove for the first time that the rocks beneath our feet are layered through time. His work launched the science of geology - the study of Earth's structure.
Exposed layers of rock. William Smith used fossils to identify rock layers and compare their order in different locations. © Rob Farrow, CC BY-SA 2.0
William Smith was a blacksmith’s son from Oxfordshire, and received little schooling. But he was bright, and worked his way up to become an engineer.
While working on canal-building projects around the UK, he noticed the rock types changed the deeper you dug and, crucially, so did the fossils.
Smith realised that there were layers of rocks beneath our feet, laid down in a fixed order over millions of years. By noticing that fossils changed with time, Smith also paved the way for later theories of evolution.
Ammonites were particularly abundant in the rocks Smith looked at. Now extinct, these molluscs jet propelled themselves through the ocean more than 65 million years ago.
Illustration of ammonites and other fossils from William Smith's 'Strata Identified by Organized Fossils'.
The ammonites species in each rock layer were easy to identify. Since different species lived at different times, their fossils were like time capsules, telling Smith how old the layers were.
Smith used rocks and fossils collected on his travels to create the first geological map of an entire country. The map showing England, Wales and part of Scotland was officially published in 1815. The patchwork of colours not only shows the different rock layers exposed by the folding and tilting of Earth’s crust, it reveals their order.
William Smith's map was the first to show the geology of an entire country.
More than 2m tall, the map is a beautiful work of art as well as a scientific triumph.
At the time, the Geological Society resented Smith’s achievement. They produced a rival map, largely copied from Smith’s, which undercut his sales. Bankrupt, he sold his precious fossil collection to the British Museum. They are now cared for by the Natural History Museum.
After 13 years of poverty, Smith was finally recognised as the father of geology. Although he was never elected to the Geological Society, they awarded him their first Wollaston Medal for geology in 1831.
Until Smith’s revelation, European scientists were guided by the Bible for their research. Geology has proven that the Earth is billions of years older than the Bible implies, and that our planet is changing constantly.
The fossils that were key to Smith’s work, such as these ammonites, are now highly prized.