Salt in Sicily lies in layers, like a stack of pancakes. Each layer is one year: in summer, water evaporated and salt settled on the bottom. In the Realmonte mine, there are 120 such layers, and at the Pasquasia cliff, nearly 1800. Layer thickness varies: in a rainy year, less salt; in a dry year, more. The result is a stone chronicle of weather.
By measuring the thickness of all layers, scientists found repeating rhythms: 3–5 years, 9 years, 11–13 years, 20–27 years, and 50–100 years. These same rhythms exist in the modern climate; for example, El Niño recurs every 3–7 years. So even when the Mediterranean Sea turned into brine, the climate pulsed under the same celestial forces as it does today.
The average thickness of an annual salt layer in Realmonte is 15.1 cm, comparable to the growth rate of salt 'trees' in modern salt ponds (about 10 cm per year). This means that in a single decade, one and a half meters of pure salt accumulated.
In Kim Stanley Robinson's novel 'Forty Signs of Rain', ocean climate oscillations become the key to weather prediction; here, the same rhythms are etched in stone six million years old.