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Other naturalists used these hypotheses to construct a history of Earth, though their timelines were inexact as they did not know how long it took to lay down stratigraphic layers.
In 1830, the geologist Charles Lyell, developing ideas found in Scottish natural philosopher James Hutton, popularized the concept that the features of Earth were in perpetual change, eroding and reforming continuously, and the rate of this change was roughly constant.
He determined that the oceans were about 80 to 100 million years old.
By the process of radioactive decay of radioactive isotopes occurring in a rock, exotic elements can be introduced over time.
By measuring the concentration of the stable end product of the decay, coupled with knowledge of the half life and initial concentration of the decaying element, the age of the rock can be calculated.
Studies of strata, the layering of rock and earth, gave naturalists an appreciation that Earth may have been through many changes during its existence.
These layers often contained fossilized remains of unknown creatures, leading some to interpret a progression of organisms from layer to layer.
Charles Darwin's son, astronomer George Darwin of the University of Cambridge, proposed that Earth and Moon had broken apart in their early days when they were both molten.