By the early 1800s, many scientists already recognized life on Earth was ancient, had changed over time, and fossils represented prehistoric extinct creatures. Evolution wasn’t a new idea, but understanding how it worked awaited Charles Darwin’s 1859 publication of “On the Origin of Species.”

Science sometimes advances by giant leaps, but more often moves in small steps by gradually gathering new evidence. The calculated age of the Earth is a good example, having shifted from a few thousand to 4.5 billion years old over the last two centuries.