Note 163 — VI HUMAN HISTORY
Reading edition
Jolly, Science Progress, 1914, No. 33, p. 41, states that there are four methods of estimating the duration of the whole period, by considering (1) the thickness of the sediment, (2) the mass of the sediment, (3) the sodium contained in the sea, and (4) radioactive transformation. (1) gives about 100 to 134 million years, (2) about 87 million years, (3) about 80 to 90 million years, and (4) a much longer period.