His studies of phosphorus deposits and banded iron formations in sedimentary rocks made him an early adherent of the "snowball Earth" hypothesis postulating that the planet's surface froze more than 650 million years ago.
Studinya mengenai deposit fosfor dan banded iron formations dalam sedimen membuatnya pendukung awal hipotesis "snowball Earth" dengan postulasi bahwa permukaan planet beku lebih dari 650 juta tahun lalu.