Subaerial Emergence of Continents on Archean Earth

Abstract

The emergence of continental crust above sea level influences Earth's surface environments and climate patterns, and it creates diverse habitats that promote biodiversity. Earth exhibits bimodal hypsometry with elevated continents and a submerged seafloor. However, it remains elusive when and how this unique feature was first established. The geological record suggests the presence of subaerial landmasses between ca. 3.8 and 2.4 billion years ago (Ga), but their spatial extent and longevity remain unclear. Further, the tectonic processes governing the proportion of continental land to ocean basins and topography during this period are poorly understood. Here, we synthesize a variety of geological and geochemical proxies to suggest that crustal emergence did occur in the early-to-mid Archean, primarily exposing precratonized volcanic crust for brief time periods. Stable continental crust on a regional scale (as cratons) began emerging around ca. 3.2–3.0 Ga, facilitated by the development of thick, stable cratonic lithospheres. Over hundreds of millions of years, voluminous magmatism within a plateau-type setting led to the formation of thick, felsic crust and depleted mantle keels, allowing cratons to rise above sea level via isostatic adjustment. The areal extent of emergent land increased from ca. 3.0 to 2.5 Ga owing to the formation of more cratons, likely coinciding with the onset of plate tectonics, and culminated around ca. 2.5–2.2 Ga when land surface area and freeboard conditions resembled those observed today. These newly emerged landmasses possibly played a critical role in oxygenating the atmosphere and oceans, cooling the climate, and promoting biodiversity during the late Archean to early Paleoproterozoic. ▪ Continental emergence marks a pivotal moment in Earth's history, impacting the planet's atmosphere, oceans, climate, and life evolution. ▪ We review the rock record to infer the timing, nature, and tectonic drivers of continental emergence on early Earth. ▪ Emergence on early Archean Earth was mostly transient, exposing primarily volcanic crust. ▪ First stable continental land formed at ca. 3.2–3.0 Ga due to the development of thick cratons and their isostatic adjustment. ▪ Emergent land area increased from ca. 3.0 to 2.5 Ga as more cratons formed and plate tectonics began.