Unit 3: Evolution. How does the theory of evolution by natural selection demonstrate the scientific...

Unit 3: Evolution

How does the theory of evolution by natural selection demonstrate the scientific process?

• Science relies on evidence to explain observations of the natural world

• Evolution is a theory: a well-supported explanation based on many observations– NOT a law.

Evolution• The change in species over time

Geologic Time Scale

• Geologic time scale: scale used by paleontologists to represent evolutionary time

• Radioactive dating has been used to assign specific ages to rock layers

• Precambrian comes first– Covers 88% of Earth’s history

• After Precambrian time, divisions of time are eras and period

• Era: 3 time periods from Precambrian until present– Paleozoic: 544 mya 245 mya– Mesozoic: 245 mya to 65 mya– Cenozoic: 65 mya to present

• Period: Eras subdivided into smaller units of time called periods– Ex. Mesozoic Era made up

of 3 periods• Triassic, Jurassic, and

Cretaceous

Mesozoic

Cenozoic

• The Fossil Record– Fossils= remains of

ancient life– Comparing fossils in

older/younger rock layers

– Provides evidence about the history of life on Earth. It also shows how different groups of organisms have changed over time

• Paleontologists: Scientists who study fossils– Make inferences about structure, what organisms

ate, where they lived

• More than 99% of all species that have ever lived on earth have gone Extinct: died out

How Fossils Form• Either the remains or some trace of its

presence must be preserved• Most formed in sedimentary rock– Organisms sink to bottom and become buried in

sediment

Interpreting Fossil Evidence

• Relative Dating: Age of fossil determined by comparing its placement with that of fossils in other layers of rock– Does not provide absolute age

• Index fossils: A fossil species that is easily recognized and must have existed for a short time but in a wide geographic range– Used to compare fossils

Radioactive dating• Radioactive dating: use of half-lives to

determine age of a sample• Half-life: Length of time required for half of

the radioactive atoms in a sample to decay

Comparative Anatomy

• Homologous Body Structure– Homologous structures: structures that have

different mature forms but develop from the same embryonic tissues• All 4 limbed vertebrates from common ancestor

• Vestigial organs: organ that serves no useful function– Ex. Legs in skinks

• Similarities in Embryology– Early stages of animals with backbones similar

Biogeography

• Biogeography is the study of the distribution of species, organisms, and ecosystems in space and through geological time.

• Geographic Isolation: Two populations are separated physically by geographic barriers such as rivers, mountains, or water

Scientific Explanations for the Origin of Life on Earth

Spontaneous Generation• living organisms from inanimate objects• Francesco Redi disproved spontaneous

generation for large organisms by showing that maggots arose from meat only when flies laid eggs in the meat.

Louis Pasteur's 1859 experiment put the question to rest. He boiled a meat broth in a flask that had a long neck which curved downward, like a goose. The idea being that the bend in the neck prevented any particles from reaching the broth, while still allowing the free flow of air. The flask remained free of growth for an extended period. When the flask was turned so that particles could fall down the bends, the broth became quickly clouded.

Miller and Urey experiment•Attempts to create life in

the laboratory•Provide a mixture of gases

similar to that in the early atmosphere

•Provide water to simulate oceans or pools

•Provide a source of energy

• Chemical Synthesis- “Primordial Soup”

• Electricity was passed through the apparatus

• Amino Acids and hydrocarbons were synthesized

Hydrothermal Vents• this environment provides the necessary

gases, energy, & a possible source of catalysts

Panspermia• Living organisms were “seeded” on Earth as

“passengers” aboard comets & asteroids from other planets that did support life

How do these competing hypotheses demonstrate the scientific process?

• The strength or usefulness of a scientific claim is evaluated through scientific argumentation– Depends on

• critical and logical thinking• active consideration of alternative scientific explanations

to explain the data presented

– It is a STRENGTH in science to have competing explanations from scientists• They are a source of new, testable ideas that have the

potential to add new evidence to support one or another of the explanations