Spreading Planet

To one who thoughtfully ponders the centuries and surveys the whole in the clear light of the spring, oceans and continents alone are of account.

—Johann von Goethe (1808), Faust geologic time

Time and space (Fig. 2.3) provide the conceptual framework for interpreting events, entities, and phenomena that influence the Earth system (Fig. 6.1). Most of Earth's history is written in the rocks and sediments over geological time scales involving the transformation of oceanic and continental environments during millions and billions of years. Moreover, geologic phenomena influence the evolution and extinction of species, creating wholesale changes in the ecosystems that characterize different eras of the Earth system (Fig. 1.6).

Geologic time, however, is only a relative term. For example, within a geologic era climate conditions can shift with the advance and retreat of ice masses on Earth. Such glacial-interglacial cycles can extend across tens of millennia with ice-volume changes that alter sea level, ocean circulation, atmospheric connections, and habitat characteristics across the planet.

Within a given climatic period, populations persist along with their aquatic or terrestrial habitats over ecological time scales. Based on the species' adaptations, populations may even survive in a single location for millennia as exemplified by stands of bristlecone pines (Pinus longaeva) in the White Mountains of California or banks of moss (Polytrichum alpestre and Chorisodontium aciphylum) in the Antarctic Peninsula region that are 5000 to 6000 years old.

Along with their spatial dimensions, geological and ecological periods reveal

0 0

Post a comment