DATING FOSSILS
Determining a fossil’s age: can’t determine age from fossil directly-must date the rocks
embedded inside or around fossil-more accurate
Relative age dating: determining the order something occurs in relation to something to
something else. You might be younger than your brother but older than your sister-that is your
relative age. Layers of earth-bottom layers are oldest and top layers youngest.
Absolute age dating: More precise than relative age dating (your birthday is absolute age
dating). Measure radioactive decay in rocks which occurs at a predictable rate. Unstable isotopes
convert to stable isotopes over time, the ratio of unstable to stable isotopes allows us to date the
rock.
EXTINCTION & EVOLUTION
Extinction: occurs when the last individual organism of a species dies
Sudden changes: Volcanic eruption or meteorite strike immediately alters global climate and
food web
Gradual changes: tectonic plates move forming mountains or oceans. These changes can isolate
species (no access to resources) or sea level changes can also hurt species.
EVOLUTION AND EVIDENCE
Biological evolution: change over time in populations of related organisms.
Hyracotherium=>Horse (pg 213 or 227 in textbook)
Living species that are closely related (horse & donkey) share a common ancestor and the degree
to which they are related (closely-distant) depends on how closely in time they diverged or split
from the common ancestor.
Comparative Anatomy: study of similarities and differences among structures of living species.
Robins, hawks and finches are easy to see similarities (beaks, feathers, wings) as is tigers,
leopards and house cats. Now compare hawks and cats…what do you think?
Homologous structures: body parts of an organism that are similar in structure and position but
different in function. Humans use arms to grasp and for balance, cats use their forelimbs to run,
walk or jump, frogs use them to jump, bats and birds use their forelimbs to fly (wings). Different
but all exhibit similar patterns. When creatures have homologous structures, this suggest species
are related. The more similar, the more likely it is two species evolved from a recent common
ancestor.
Analogous structures: body parts that perform a similar function but differ in structure. Birds vs
flies. Birds wings have feathers, flies have tiny hairs. The amount of differences in these
structures indicates that birds and flies are NOT closely related.
Vestigial Structures: body parts that lost their original function through evolution. It is believed
that a vestigial structure is related to an ancestral species that used the structure for a particular
purpose. Remember whales having legs? The pelvic bones left behind are vestigial structures.
Embryology: science of the development of embryos from fertilization to birth. Embryos of
different species often resemble each other at different stages of development. All vertebrate
embryos have pharyngeal pouches at one stage which develops into different body parts in each
vertebrate but always in the face or neck. Humans, reptiles and birds=develops into gland in neck
that regulates calcium. In fish, it becomes gills which also regulates calcium. Similarities in
function and location of gills suggests strong evolutionary relationship between fish and other
vertebrates.
Molecular biology: study of gene structure and function. Gene mutations are the source of
variations upon which natural selection acts. All organisms have genes, all genes are made of
DNA and all genes work in similar ways which supports premise that all organisms are related.
By comparing genes and proteins, scientists see how closely related two species are.