Expanding Earth

Expanding Earth is the hypothesis that Earth’s radius increased substantially over geological time, moving continents apart without conventional plate tectonics.

Earth's Radius: The distance from Earth's center to its surface, varying slightly with latitude and topography. The hypothesis depends on this quantity increasing substantially through geological time.
Ott Christoph Hilgenberg: A German geophysicist who published an early model of an expanding Earth in 1933. His small-globe reconstructions became a prominent visual argument for expansion.
Plate Tectonics: The theory that Earth's lithosphere consists of moving plates driven by mantle processes and their interactions. It explains seafloor creation, subduction, and continental motion while retaining nearly constant Earth size.
Hilgenberg's Expanding Earth Model: A reconstruction placing present-day continents on a smaller Earth to suggest they once formed a continuous covering. It is a canonical illustration of how expansion was used to fit continental outlines together.
Paleomagnetism: The study of ancient magnetic fields recorded in rocks, used to reconstruct past plate positions and motions. Magnetic records provide evidence for continental movement that expanding-Earth models must accommodate.
Samuel Warren Carey: An Australian geologist who advocated an expanding Earth and developed versions of the hypothesis. Carey kept the hypothesis in scientific discussion after plate tectonics gained acceptance.
Seafloor Spreading: The creation of oceanic lithosphere at mid-ocean ridges as tectonic plates move apart. It accounts for new ocean floor through ridge creation balanced by destruction at subduction zones.
Carey's Expanding Earth Model: A version of the expanding-Earth hypothesis developed by geologist Samuel Warren Carey. Carey's model shows how the hypothesis persisted alongside the rise of plate tectonics.
Oceanic Crust: The relatively thin, dense outer layer of Earth beneath ocean basins, continually created and recycled by plate tectonics. A growing-Earth explanation must account for the area and age distribution of oceanic crust.
Alfred Wegener: A German scientist who proposed continental drift, arguing that continents had once been joined. Wegener's evidence for shifting continents helped motivate later explanations, including Earth expansion.

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