Andrew Alden of About explains that Australian geologist Sam Carey's theory of Earth expansion, the idea that the continents fit together properly only on a formerly smaller Earth, once rivaled the theory of plate tectonics. Carey's ideas expanded upon Wegener's continental-drift theory and hypothesised that the continents fit together properly on a shrunken Earth. From about the 1930s to the 1950s, this idea of Earth expansion remained a legitimate hypothesis.
Alden explains that many people still believe the Earth expands in size, but their work further demonstrates plate tectonics. However, he also argues that Carey used the curving lines of mountain ranges, long seafloor chasms, island chains and the patterns of earthquakes and eruptions to paint vivid portraits of Earth bursting its seams and stretching into its modern state with two distinct kinds of crusts. Carey's theories proposed that the original continental crust remained in its current torn pieces with the newer and different oceanic crust between them. Alden explains that the doubts about Carey's theories actually helped formulate the now accepted ideas of plate tectonics, with Carey's detractors creating good maps of the seafloor, making progress in seismology by creating large paleomagnetic databases and making precise measurements of crustal motions.