Geologic Youth of Galápagos Islands Confirmed by Marine Stratigraphy and Paleontology

Abstract

Six distinctive types of fossiliferous marine deposits occur on the Galádpagos Islands that provide evidence for the age of emergence of the islands above sea level and hence a maximum age for the islands' terrestrial biota. These subtidal to supratidal deposits include (i) volcanic tuffs with fossils, (ii) limestones and sandstones interbedded with basalt, (iii) terrace deposits, (iv) beach rock, (v) supratidal talus deposits, and (vi) recently uplifted tidal and subtidal rocks and sand. With the exception of (vi), the deposits were previously assigned ages varying from Miocene to Pleistocene, but all are less than about 2 million years old. This age, together with independently determined geologic ages, indicate that the islands emerged from the sea relatively recently and that all evolution of the islands' unique terrestrial biota occurred within the past 3 to 4 million years.

Colonization and diversification of Galápagos terrestrial fauna: a phylogenetic and biogeographical synthesis

“…The age of the islands increases moving eastward along the plate, with the oldest islands located towards the southeast of the archipelago. K-Ar age determinations and marine fossils indicate a maximum age of the oldest land of the order of 3 Ma, whereas geological plate motion models set a maximum age of emergence around 4 Ma, depending on the velocity of the Nazca plate (Hickman & Lipps 1985;White et al 1993;Geist 1996;D. Geist 2005D.…”

Nuclear and mitochondrial sequences confirm complex colonization patterns and clear species boundaries for flightless weevils in the Galápagos archipelago

“…By contrast, such explanations are not generally required to reconcile divergence times with the ages of the extant islands in other dynamic volcanic island systems such as the Canary and Hawaiian Islands (Fleischer et al 1998;Emerson et al 2000a,c;Gubitz et al 2000;Price & Clague 2002;Hormiga et al 2003;Emerson & Oromí 2005). Previous analyses of Galapaganus with the penalized likelihood (PL) age estimation method (Sanderson 2002) and the use of an extrinsic clock (employing published calibrations for invertebrate mitochondrial divergences; Sequeira et al 2000) indicate that the age of island endemics and presumably that of the colonization of the archipelago by the ancestor of all island endemics (8.6-12 Ma) exceeds the geological estimates of the extant emerged islands (Cox 1983;Hickman & Lipps 1985). Explanations of this discordance could invoke geological evidence of older, drowned islands as potential colonization platforms for ancestors, effectively extending the time available for species diversification beyond the ages of the extant emerged islands (Christie et al 1992;Werner et al 1999).…”

Biogeographic origins of Darwin's finches (Thraupidae: Coerebinae)

“…The Galápagos Islands are located on the Nazca plate, and are the product of a volcanic hotspot (Christie et al 1992). The young hypothesized age of the current islands (4-5 mya; Hickman and Lipps 1985), along with the Nazca plate's eastern movement, indicate the Galápa-gos Islands were never part of the mainland, and have never been located closer to mainland South America. Although the greater distance between Caribbean islands and the Galápagos might make a direct Caribbean-toGalápagos dispersal seem unlikely, birds have previously demonstrated the ability to disperse long distances.…”