Bio Chapter 20

What do fossils reveal about ancient life?

Fossils reveal information about the structures of ancient organisms, the sequential nature of groups in the fossil record, evolution from common ancestors, and the ecology of ancient environments.

How do we date events in Earth’s history?

Relative dating helps paleontologists to determine whether a fossil is older or younger than other fossils.

Radiometric dating uses the proportion of radioactive isotopes to stable isotopes to calculate the age of a sample.

How was the geologic time scale established, and what are its major divisions?

he geologic time scale is based on both relative and absolute dating. The major divisions of the geologic time scale are eons, eras, and periods.

How have Earth’s physical and biological environments shaped the history of life?

Global climate change, mountain building, the emergence of islands, continental drift, changes in levels of continents and oceans, and meteor impacts have altered Earth’s habitats, with major effects on the history of life.

The actions of living organisms over time have changed conditions in the atmosphere, the oceans, and the land.

extinct

term used to refer to a species that has died out and has no living members.

relative dating

method of determining the age of a fossil by comparing its placement with that of fossils in other rock layers.

index fossil

distinctive fossil that is used to compare the relative ages of fossils

radiometric dating

method for determining the age of a sample from the amount of a radioactive isotope to the nonradioactive isotope of the same element in a sample.

half-life

length of time required for half of the radioactive atoms in a sample to decay.

geologic time scale

timeline used to represent Earth’s history

era

major division of geologic time; usually divided into two or more periods.

period

division of geologic time into which eras are subdivided.

plate tectonics

geologic processes, such as continental drift, volcanoes, and earthquakes, resulting from plate movement.

What elements are used in radioactive dating?

Carbon-14, Potassium-40, uranium-238, and rubidium-87

What are the four eons?

The Hadean Eon, The Archean Eon, Proterozoic Eon, and the The Phanerozoic.

What distinguishes the four eons?

The Hadean Eon, during which the first rocks formed, spanned the time from Earth’s formation to about 4 billion years ago.

The Archean Eon, during which life first appeared, followed the Hadean.

Proterozoic Eon, stable continents began to form, and eukaryotic cells evolved.

The Phanerozoic (fan ur uh zoh ic) Eon began at the end of the Proterozoic and continues to the present.

What patterns describe the sequential nature of groups in the fossil record?

The emergence, growth, and extinction of larger clades, such as dinosaurs, mammals, or flowering plants, are examples of macroevolutionary patterns.

What does the fossil record show about periods of stasis and rapid change?

Fossil evidence supports the hypothesis that evolution can occur at different rates in different clades, and at different times

Now and then, the fossil record shows that equilibrium can be interrupted by brief periods of geologically rapid change.

What are two patterns of macroevolution?

Two important patterns of macroevolution are adaptive radiation and convergent evolution.

What evolutionary characteristics are typical of coevolving species?

The relationship between coevolving organisms often becomes so specific that neither organism can survive without the other. Evolutionary change in one organism is usually followed by a change in the other organism.

macroevolutionary pattern

changes in anatomy, phylogeny, and behavior that take place in clades larger than a single species.

background extinction

extinction caused by slow and steady process of natural selection

mass extinction

event during which many species become extinct during a relatively short period of time

gradualism

the evolution of a species by gradual accumulation of small genetic changes over long periods of time.

punctuated equilibrium

pattern of evolution in which long stable periods are interrupted by brief periods of more rapid change.

adaptive radiation

process by which a single species or a small group of species evolves into several different forms that live in different ways.

convergent evolution

process by which unrelated organisms independently evolve similarities when adapting to similar environments.

coevolution

process by which two species evolve in response to changes in each other over time.

What do scientists hypothesize about early Earth and the origin of life?

Earth’s early atmosphere contained little or no oxygen. It was mainly composed of carbon dioxide, water vapor, and nitrogen, with smaller amounts of carbon monoxide, hydrogen sulfide, and hydrogen cyanideMiller and Urey’s experiment suggests that organic compounds necessary for life could have arisen from simpler compounds on a primitive Earth.

The “RNA world” hypothesis proposes that RNA existed before DNA. From this simple RNA-based system, several steps could have led to today’s DNA-directed protein synthesis.

What theory explains the origin of eukaryotic cells?

A great deal of evidence now supports the theory that many of the complex features of eukaryotic cells evolved through endosymbiosis.

endosymbiotic theory

theory that proposes that eukaryotic cells formed from a symbiotic relationship among several different prokaryotic cells.

The Miller-Urey experiment

In 1953, chemists Stanley Miller and Harold Urey tried to test the hypothesis that organic compounds could have been produced on early Earth.