* James Hutton: A Scottish geologist, often called the "Father of Modern Geology," who proposed in the late 1700s that the Earth was shaped by gradual processes over incredibly long periods, challenging the prevailing belief in a young Earth.
* Charles Lyell: A British geologist who, in the early 1800s, popularized Hutton's ideas and further developed them in his influential book "Principles of Geology." Lyell's work strongly influenced Darwin's thinking about the vast timescales necessary for evolution to occur.
It's important to note that Darwin's contemporaries, like Lyell, recognized the Earth's ancient age, but they relied on geological evidence and lacked the tools to determine an accurate age. It wasn't until the development of radiometric dating in the 20th century that scientists could estimate the Earth's age with greater precision.
