sentence: In 1895, John Perry, a former assistant to Kelvin, produced an age of Earth estimate of 2 to 3 billion years old using a model of a convective mantle and thin crust.
modified: In 1895, John Perry, an former assistant to Kelvin, produced a age of Earth estimate of 2 to 3 billion years old using an model of an convective mantle and thin crust.