Changes

Around the same time [[Lord Kelvin]] put his mind to deriving an age, and came up with a range between 20 million years and 400 million years.  He later refined that down to between 20 million and 40 million years.<ref name="ingv" />

Around the same time [[Lord Kelvin]] put his mind to deriving an age, and came up with a range between 20 million years and 400 million years.  He later refined that down to between 20 million and 40 million years.<ref name="ingv" />

The 1911 edition of the [[Encyclopedia Britannica]] discussed dates up to 500 million years.<ref>Encyclopedia Britannica, pp 650-651.</ref>

The 1911 edition of the [[Encyclopædia Britannica]] discussed dates up to 500 million years.<ref>Encyclopædia Britannica, pp 650-651.</ref>

By about 1930, J. H. Jeans was arguing for an age of the Earth of around 2,000 million years.<ref>Universal History of the World, p.76.</ref>

By about 1930, J. H. Jeans was arguing for an age of the Earth of around 2,000 million years.<ref>Universal History of the World, p.76.</ref>

The currently-proposed age is 4,500 million years, based in part on rocks dated by [[Potassium-Argon]] (K:Ar) dating at about 4,400 millions years.<ref>Peck, 2000, p.376.</ref>

The currently-proposed age is 4,500 million years, based in part on rocks dated by [[Potassium-argon dating|Potassium-argon (K:Ar) dating]] at about 4,400 millions years.<ref>Peck, 2000, p.376.</ref>

== Bibliography ==

== Bibliography ==