appears in letters Darwin wrote between 1856 and 1863, and was also used in a response by Charles Lyell. By this time, geologists recognised that the Earth was millions of years old. The exact chronology proposed by Darwin was disputed by other geologists, and the leading physicist William Thomson (later ennobled as Lord Kelvin) produced an analyses of the heat energy and thermal histories of the Earth and Sun which yielded age estimates that were too short for gradual evolution. Thomson's colleague Fleeming Jenkin wrote an 1867 review of Darwin's On the Origin of species which opposed evolution on the basis of the shortened time available. Kelvin's age paradox was not resolved until it was discovered in the 20th century that the Earth is heated by radioactive decay, that its internal thermal gradient is affected by mantle convection, and that the Sun is heated by nuclear fusion. Since the 1980s, the big-bang theory has been the prevailing cosmological model for the universe. It was envisioned by a Roman Catholic priest, Monsignor Georges Lemaître in the 1930s. Lemaître suggested that the evident expansion of the universe, if projected back in time, meant that at some finite time in the past all the mass of the universe was concentrated into a single point, a "primeval atom" where and when the fabric of time and space came into existence. However, in the 1920s and 1930s almost every major cosmologist subscribed to a view that the universe is in an eternal steady state. After Lemaître proposed his theory, some scientists complained that its assumption that time had a beginning amounted to a reimportation of religious concepts into physics. When the expression "Big Bang" was coined by Fred Hoyle in 1949, he meant it to be slightly pejorative, but the term stuck and gained currency. Lemaître himself concluded that an initial "creation-like" event must have occurred. The Big-Bang is contrary to young-Earth creationism, sensu stricto. But it has been welcomed by other Christian creeds, and it is in line with the Roman Catholic concept of creation. Under the Anthropic principle, by which the properties of the universe is seemingly fine-tuned for our own existence, some Christians see evidence that a divine creator has purposefully designed the universe. Pre-scientific era Early history David Sedley, in his book Creationism and Its Critics in Antiquity, traces creationist thought to the presocratic thinkers Anaxagoras and Empedocles, in the 5th