History of the Biosphere

Three reasons the fossil record is biased or incomplete

Fossilization is rare; organisms with hard parts fossilize more easily; species that were abundant and long-lived are overrepresented; fossils form only in certain environments

How are relative ages established in the fossil record?

By the position of fossils in sedimentary rock layers (strata), where deeper layers are older than layers above them

What technique is used to determine absolute ages of fossils?

Radiometric dating

How does radiometric dating work (include half-life)?

It measures decay of radioactive isotopes; half-life is the time for half of the isotope to decay, allowing age calculation

Four eons of the geologic record and their time ranges

Hadean (4.6–4 BYA); Archaean (4–2.5 BYA); Proterozoic (2.5 BYA–541 MYA); Phanerozoic (541 MYA–present)

Two major events of the Hadean Eon

Formation of Earth and solar system; accumulation of water and early organic compounds

Two major events of the Archaean Eon

First prokaryotic life (stromatolites); oxygen production begins increasing in atmosphere

Two major events of the Proterozoic Eon

Rise of atmospheric oxygen enabling aerobic life; origin of eukaryotes and multicellular organisms

How does plate tectonics influence biodiversity?

Moves continents, changing habitats and isolating populations, leading to speciation

How does continental drift influence biodiversity?

Separates and reconnects landmasses, altering species distribution and evolution

How do mass extinctions influence biodiversity?

Rapidly eliminate many species, opening niches for new species to evolve

How do adaptive radiations influence biodiversity?

Rapid diversification of species into new ecological niches after disturbances

Paleozoic Era time range

541–252 million years ago

Two major events in the Paleozoic Era and their impact

Cambrian Explosion increased biodiversity rapidly; colonization of land by plants and animals created new ecosystems

Mesozoic Era time range

252–66 million years ago

Two major events in the Mesozoic Era and their impact

Dominance of dinosaurs increased vertebrate diversity; evolution of mammals, birds, and flowering plants expanded ecosystems

Cenozoic Era time range

66 million years ago–present

Two major events in the Cenozoic Era and their impact

Diversification of mammals and grasses reshaped ecosystems; evolution of modern species including humans increased biodiversity