Final answer:
Charles Darwin adopted the concept of Earth's great age from Charles Lyell, which was integral to Darwin's theory of evolution. Earth's antiquity, suggested by Lyell's gradual geological processes, provided the timeframe necessary for the slow and gradual changes entailed in natural selection.
Step-by-step explanation:
From the work of Charles Lyell, a prominent geologist, Charles Darwin acquired the concept of the Earth being far older than the commonly accepted 6,000 years. Lyell, in his book Principles of Geology, argued that geological processes were gradual and shaped the Earth's surface over a vast period of time. This perspective on Earth's antiquity was a critical component Darwin incorporated into his theory of evolution, giving enough time for the gradual process of natural selection to produce the diversity of life observed.
Through Lyell's ideas of a constantly changing Earth, Darwin understood that the geological changes could occur over extended periods. This was evident to Darwin when he found fossils of marine life high in the Andes mountains during his voyage on the Beagle, suggesting that these mountains had risen from beneath the sea over millennia. The timescale for such changes supported Darwin's theory that species could evolve gradually over long periods.
Darwin saw the connection between Lyell's slow geological changes and the potential for biological evolution by natural selection, which was crucial in the development of his own theory. Combined with the influence from others such as Malthus and Lamarck, and his own observations, Darwin formulated his theory of evolution that emphasized how small, incremental changes in traits could lead to significant biological diversity over vast stretches of time.