The age of the earth could not be accurately gauged until radioactivity was understood, and this did not occur until the 20th century. All of our concepts of the age, size, and geological dynamics of the Solar System are essentially brand new.

As late as 1870, the source of the Sun's power was thought to be due to conversion of gravitational potential to heat by contraction. With this scheme the Sun could live some 30 million years, which was considered to be an aeon of time. Darwin however had estimated some time earlier that the Earth was at least 10 times older, based on rates of erosion. Of course all these speculations were completely wrong, because the source of heat in the Earth is radioactivity, and in the Sun nuclear fusion. The necessarily relatively short life of the Sun was adduced by so great a scientist as Lord Kelvin as evidence against Darwin and evolution.

It was with absolute astonishment that people gradually realized that both the Sun and the Earth are billions of years old. Even then, it was not known that the "spiral nebulae" were in fact remote galaxies like our own. Thus the scale of the Universe was not even in the ballpark until the 1920s. Wegener's theory of continental drift, posited near the turn of the century, was not accepted until the 1950s. Thus we can date our modern worldview to about 1955.