Holmes, Arthur (1890-1965) was a British geologist who used radioactivity to determine the age of rocks, which led to new estimations of the earth's age.

Holmes was born on Jan. 14, 1890, in Hebburn-on-Tyne, England. He graduated from Gateshead High School and, in 1907, attended Imperial College in London. In 1909, he received his bachelor's degree in mathematics and physics. A year later, he graduated as an Associate of the Royal College of Science. While doing postgraduate studies on rocks, Holmes compared the amounts of the radioactive elements uranium and thorium to figure out geological time. He figured the minimum age of the earth to be 1,600 million years. Also that year, he went to Mozambique on a geologic expedition. In 1912, he accepted a teaching position at Imperial College.

From 1920 to 1924, Holmes worked for the Yomah Oil Company in Burma as chief geologist. On his return to England, he was asked to start a new geology department at Durham University. In 1929, Holmes proposed a modification of Alfred Wegener 's theory on continental drift. He believed the cause of the earth's movements was subcrustal convection currents. He theorized that the continental rocks were lighter and resisted being submerged and that the heavier oceanic rocks were pushed back down to the mantle. New evidence eventually helped support his theory.

Holmes moved to Edinburg University to become Regius Chair of Geology and Mineralogy in 1942. In 1944, he was elected to the Royal Society. Two years later, he published his best-known and most important work, Principles of Physical Geology. The book was well received because it helped clarify the confusing field of geology.

Holmes married Margaret Howe in 1914. After her death, Holmes married Dr. Doris Livesey Reynolds in 1939. Holmes died on Sept. 20, 1965.