Chapter 25 - The History of Life on Earth

When did Earth form?

~ 4.6 bya

When did life first appear?

~ 3.7-4.0 bya (evidence from stromatolites)

What are the 4 predicted steps in the origin of life?

Abiotic synthesis of small organic molecules, formation of macromolecules, packaging into protocells, origin of self replicating molecules (RNA)

What are protocells?

Membrane bound droplets that can maintain an internal environment and show simple metabolism and reproduction

What is the RNA world hypothesis?

The idea that RNA was the first genetic material, capable of both storing information and causing reactions

What does LUCA stand for?

Last Universal Common Ancestor, the shared ancestor of all living things

Where are most fossils found?

In layers of sedimentary rock called strata

Why is fossil record biased?

Favors species that were widespread, abundant, long lived, and had hard parts

What is radiometric dating used for?

Determining the absolute age of fossils using isotopes

When did the first prokaryotes appear?

~ 3.5 bya

What caused the Oxygen Revolution (~ 2.7 bya)?

Cyanobacteria released O2 (did photosynthesis), which accumulated in the atmosphere

When did the first eukaryotes appear?

~ 2.1 bya

What is the Cambrian explosion?

A period (~ 535 mya) when most major animal phyla appeared in the fossil record

When did organisms colonize land?

~ 500 mya (fungi, plants, animals together)

When did humans diverge from other primates?

~ 6-7 mya

What is plate tectonics?

The theory that Earth’s crust is divided into plates that move slowly over time

How does continental drift affect evolution?

Changes habitats, isolates populations, caused speciation and extinction

What is a mass extinction?

A widespread, rapid loss of many species caused by major environmental changes

What caused the Permian extinction (252 mya)?

Volcanic activity, climate change, ~ 96% marine species extinct

What caused the Cretaceous extinction (66 mya)?

Asteroid impact + volcanic activity, killed dinosaurs (except birds)

Are we in a 6th mass extinction?

Possibly, current rates are 100-1000x higher than the background rate, mostly due to humans

What is adaptive radiation?

When a group of organisms rapidly evolves into many species to fill new ecological niches

What often triggers adaptive radiations?

Mass extinctions, new habitats, or key innovations (like seeds or flight)

Example of a global adaptive radiation?

Mammals expanding after the extinction of dinosaurs

What are exaptations?

Structures that evolved for one function but were later used for another (jaw bones to ear bones)

What does “evolution is not goal oriented” mean?

Evolution works by natural selection on current variation, it doesn’t plan for the future