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How do ancient shield rocks show that continents grew outward over time?

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continental landform Davis's proposed landscape-development states. The morphology shown is not actually time-indicative. For example, A could be a gully system in soft sediment or a canyon such as the Royal Gorge in Colorado, which is millions of years old. The ridge-ravine topography of B would normally develop under humid conditions, but the river meandering on alluvium indicates a prior or extraneous non-humid aggrading mechanism. The riverine plain of C implies a complex history of planation and aggradation in a current fluvial mode.

Ancient continental shields serve as the stable, ancient nuclei of continents, composed of crystalline rocks often billions of years old. Geologists use these shields to demonstrate that continents grew outward over time through the concept of accretion.1

This growth occurs as belts of younger rocks—formed through intense deformation and mountain-building episodes—are welded onto the borders of these preexisting, stable shields. The process is driven by plate tectonics, where subduction zones at continental margins generate new crust. As oceanic plates subduct, they contribute material through the accretion of volcanic island arcs and the scraping of seafloor sediments onto the continental edge.1234

Radiometric age dating provides the documentary evidence for this expansion, allowing scientists to identify and map these successively younger rock units as they were added to the ancient cores throughout geologic time.21