History of Life

Chapter 19

The Fossil Record 19.1• Any evidence of an organism that lived

long ago and are now extinct• Most are formed in sedimentary rocks• Provides info about structure, environment

and way of life

Types of Fossils

Amber-preserved

Imprint

MoldCast

Trace

How are fossils formed?

Dating Earth’s History

Relative Dating• Uses the position of fossils in sediment layers

– Oldest at the bottom layer, youngest on top, not actual age

– Index fossil• an easily recognized and widespread fossil used to

compare the relative ages of rocks, ex. trilobites

Radiometric Dating• Uses radioactive isotopes

(atoms with unstable nuclei that break down or decay)– Half-life – the time required for

half of the radioactive atoms in a sample to decay• Potassium 40, half-life = 1.3

billion years• Carbon 14, half-life = 5730 years

Geologic Time Scale

Geological Time Scale

• Based on both relative and absolute dating

• Major divisions– Eons– Eras– Periods

Precambrian Era

• Starts 4.7 bya• Life began• Accounts for 90 % of Earth’s history• Primitive prokaryote were the first forms of

life

• Paleozoic Era– Appearance of plants and animals including

fishes, reptiles, amphibians and ferns• Mesozoic Era

– Mammals and dinosaurs– Flowering plants

• Cenozoic Era– Primates– Modern human (200,000 years ago)

Life on a changing planet

• Physical forces– Geological forces (building mountains and

moving whole continents) have altered habitats of living organisms throughout Earth’s history

– Plate tectonic theory• Explains the movement of continents (3 cm/year)• Africa and South America separated by Atlantic

Ocean

• Biological forces– Actions of living organism have changed

conditions in the land, water, and atmosphere of the Earth

– Earth cooled as CO2 decreased; used by early photosynthetic organisms

Patterns and Processes of Evolution 19.2

• What processes influence survival or extinction of species and clades?– Clades

• Group of species that includes a common ancestor and all descendants of that ancestor, living or extinct.

• The more varied the species (more diversity) in a particular clade are, the more likely the clade is to survive environmental change.

Patterns of Extinction

• Background extinction– Slow steady process of natural selection

• Mass extinction– An event during which many types of living

things suddenly die out– Makes new habitats and resources available to

organisms left after a major catastrophe

Rate of Evolution

Gradualism• Species originate through a slow and steady change

of adaptations

Punctuated Equilibrium• Speciation experience long, stable periods

interrupted by brief periods of rapid evolutionary change

Patterns of Macroevolution

Adaptive radiation• When a single species or a small group of

species evolves over a relatively short time into several different forms that live in different ways.

Hawaiian honeycreepers

Convergent Evolution• Distantly related organisms evolve similar

traits• Unrelated species occupy similar

environments in different parts of the world

Coevolution

• Process by which two species evolve in response to changes in each other over time– Ex. Flowers and pollinators (birds, bees, etc.)

Earth’s Early History 19.3

• About 4.5 billion years old• Formed from cosmic debris colliding• Earth cooled enough for solid rocks to form

and water vapor to condense and fall as rain, produce oceans

• Earth’s atmosphere was primarily composed of – Carbon dioxide, water vapor, nitrogen

• Hypotheses on how life began

Stanley Miller and Harold Urey’s experiment

• Produced 21 amino acids—building blocks of proteins.

• Proved incorrect• Nonlife to life is a

big leap!

Microspheres

• Proteinoid microspheres– Contain selective permeable membrane

• Water passes through– Store and release energy– About 3.8 billion years ago

RNA and DNA

• Hypothesized that RNA formed before DNA

Origin of eukaryotic cells

Endosymbiotic theory• Prokaryotes were the ancestors of

eukaryotic organisms• Small prokaryotes began living inside the

larger cells

– Mitochodria • evolved from endosymbiotic prokaryotes that are

able to use oxygen to generate energy-rich ATP– Chloroplasts

• Evolved from endosymbiotic prokaryotes had the ability to photosynthesize

Modern evidence

• Lynn Margulis (1960)– Supported endosymbiotic theory– Mitochondria and chloroplasts have DNA

similar to bacterial DNA– Both have ribosomes resembling those of

bacteria– Reproduce by binary fission when cells

containing them divide by mitosis