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But T.C. Chamberlin, head of the Department of Geology at the [[University of Chicago]], was not prepared to concede defeat. While defending his faith in long-ages, he speculated, without any observational basis whatever, that there might yet be discovered new sources of energy that would allow more time than Kelvin had calculated.<ref>{{cite book |title=Earth |author= Frank Press, Raymond Siever |publisher=W. H. Freeman |edition=4 |year=1986 |pages=40 |isbn=978-0716717430 |url=http://www.amazon.co.uk/Earth-Frank-Press/dp/0716717433}}</ref> Thus, the quest for the age of the earth as a subjective, arbitrary and erratic pursuit, was set for an fascinating turn.<ref name="West"/> This came in 1896, when [[radioactivity]] was discovered by Henri Becquerel and when in 1903 [[Marie and Pierre Curie|Pierre Curie]] and Albert Laborde demonstrated that [[radioactive decay]] releases heat. Before long, several people argued that this source of heat was great enough to overturn Kelvin’s conclusion about the boundary for the age of the earth. Among them was [[Ernest Rutherford]], who in 1904 suggested, in the Royal Institution, that ''“Lord Kelvin had limited the Age of the Earth, ‘provided no new source of heat was discovered.’ That prophetic utterance refers to what we are considering tonight, [[radium]]!”'' Later, Rutherford often repeated his tale of thinking on his feet in front of the “old bird” Kelvin who “beamed” at him. This episode and pleasing form of the anecdote, boosted by the eminence of its author, who was considered the father of nuclear theory, provided a ready vehicle for mythmaking and uncritical acceptance of proposition that because the discovery of radioactive heat undermined an assumption behind Kelvin’s calculation, it also undermined his conclusion.<ref name="PerryKelvinCritique"/> As the half-life of radium's dominant isotope is 1600 yr, heat given out by radium obviously could not be the wanted missing energy.{{#tag:ref|cf. ''"[Rutherford and Soddy] could not get away from the fact, however, that radium itslef, although universally regarded as an element, decays far too rapidly to be as old as the minerals in which it is found. The only solution seemed to be that radium too must be a metabolon with a 'life' of a few thousends years."''<ref name ="BURCHFIELD">{{cite book |title=Lord Kelvin and the Age of the Earth |author=Joe D. Burchfield |publisher= The University of Chicago Press |place=Chicago |year=1975, 1990 |pages=173 |isbn=0-226-08043-9}}</ref>|group=note}} Nevertheless, later assumptions of equilibrium in decay series of [[uranium]] and [[thorium]] allowed to consider heat sources with half-lives in gigayears (Ga; 1 Ga = 10⁹ years).

But T.C. Chamberlin, head of the Department of Geology at the [[University of Chicago]], was not prepared to concede defeat. While defending his faith in long-ages, he speculated, without any observational basis whatever, that there might yet be discovered new sources of energy that would allow more time than Kelvin had calculated.<ref>{{cite book |title=Earth |author= Frank Press, Raymond Siever |publisher=W. H. Freeman |edition=4 |year=1986 |pages=40 |isbn=978-0716717430 |url=http://www.amazon.co.uk/Earth-Frank-Press/dp/0716717433}}</ref> Thus, the quest for the age of the earth as a subjective, arbitrary and erratic pursuit, was set for an fascinating turn.<ref name="West"/> This came in 1896, when [[radioactivity]] was discovered by Henri Becquerel and when in 1903 [[Marie and Pierre Curie|Pierre Curie]] and Albert Laborde demonstrated that [[radioactive decay]] releases heat. Before long, several people argued that this source of heat was great enough to overturn Kelvin’s conclusion about the boundary for the age of the earth. Among them was [[Ernest Rutherford]], who in 1904 suggested, in the Royal Institution, that ''“Lord Kelvin had limited the Age of the Earth, ‘provided no new source of heat was discovered.’ That prophetic utterance refers to what we are considering tonight, [[radium]]!”'' Later, Rutherford often repeated his tale of thinking on his feet in front of the “old bird” Kelvin who “beamed” at him. This episode and pleasing form of the anecdote, boosted by the eminence of its author, who was considered the father of nuclear theory, provided a ready vehicle for mythmaking and uncritical acceptance of proposition that because the discovery of radioactive heat undermined an assumption behind Kelvin’s calculation, it also undermined his conclusion.<ref name="PerryKelvinCritique"/> As the half-life of radium's dominant isotope is 1600 yr, heat given out by radium obviously could not be the wanted missing energy.{{#tag:ref|cf. ''"[Rutherford and Soddy] could not get away from the fact, however, that radium itself, although universally regarded as an element, decays far too rapidly to be as old as the minerals in which it is found. The only solution seemed to be that radium too must be a metabolon with a 'life' of a few thousand years."''<ref name ="BURCHFIELD">{{cite book |title=Lord Kelvin and the Age of the Earth |author=Joe D. Burchfield |publisher= The University of Chicago Press |place=Chicago |year=1975, 1990 |pages=173 |isbn=0-226-08043-9}}</ref>|group=note}} Nevertheless, later assumptions of equilibrium in decay series of [[uranium]] and [[thorium]] allowed to consider heat sources with half-lives in gigayears (Ga; 1 Ga = 10⁹ years).

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

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