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The fossil record documents macroevolution
is any preserved remnant or impression left by an organism that lived in the
rocks are the riches sources of fossils.
silt weathered and eroded from the land are carried by rivers to seas and swamps
where the particles settle to the bottom. Deposits pile up and compress the older sediments below into
organic substances of a dead organism buried in sediments usually decay rapidly.
that are rich in minerals may remain as fossils.
these relics are hardened even more and preserved by a process called
common fossilized plant material is pollen because it has a hard organic case
that resists degradation.
called trace fossils form in footprints, animal burrows, or other impressions
left in sediments by the activities of animals.
of the Fossil Record
discovery of a fossil is the culmination of a sequence of improbable
organism had to die in the right place at the right time.
the rock layer containing the fossil had to escape geological process that
destroy or severely distort rocks suck as erosion, pressure from superimposed
strata or the melting of rocks that occurs at some location.
fossil must later be exposed.
the remote chance that someone will find the fossil.
substantial fraction of species that have lived probably left no fossils, most
fossils that formed have been destroyed and only a fraction of the existing
fossils has been discovered.
Paleontologists use a variety of methods to date fossils
particular location, sedimentation is not continuous but occurs in intervals
when the sea level changes or lakes and swamps dry up and refill.
forms in layers or strata.
fossils in each layer are a local sampling of the organisms that existed at the
time that sediment was deposited.
sediments are superimposed upon older ones.
at one location can often be correlated with strata at another location by the
presence of similar fossils known as index fossils.
have established a geological time scale with a consistent sequence of
periods are grouped into four eras: Precambrian,
Paleozoic, Mesozoic and Cenozoic
represents a distinct age in the history of Earth and its life.
boundaries are marked in the fossil record by explosive radiations of many new
forms of life following mass extinctions.
boundaries between periods within each era also mark major transitions in the
forms of life fossilized in rocks.
periods within each era are further subdivided into finer intervals called
of the rocks is a serial that chronicles the relative ages of fossils.
not tell us the absolute ages of the embedded fossils.
dating is the method most often used to determine the ages of rocks and fossils
on a scale of absolute time.
contain isotopes of elements that accumulated in the organisms when they were
each radioactive isotope has a fixed rate of decay, it can be used to date a
isotopeís half-life is the number of years it takes for 50% of the original
sample to decay and is unaffected by temperature, pressure and other
method is using amino acids.
acids exist in two isomers with either left handed or right handed symmetry.
synthesize only left handed amino acids which are incorporated into proteins.
organism dies, its population of left handed amino acids is slowly converted
resulting in a mixture of left and right handed amino acids.
(L-amino acids = left handed and D-amino acids = right handed)
the rate at which this chemical conversion takes place, called racemization, we
can determine how long the organism has been dead.
is temperature sensitive.
Evolutionary novelties are modified version of older structures.
A. One mechanism is the gradual refinement of existing structures for new function like the comparison of bird wings to the forelimbs of dinosaurs and modern reptiles.
biological structures have an evolutionary plasticity that makes alternative
for a structure that evolved in one context and became co-opted for another
function is an explaination.
that control development play a major role in evolutionary novelty.
evolution of complex structures from the antecedents requires so much remodeling
that changes are probably involved at a large number of gene loci.
program development control the rate, timing, and spatial pattern of changes in
an organismís form as it is transfigured from a zygote into an adult.
growth is the difference in the relative rates of growth of various parts of the
body and helps shape an organism.
these relative rates of growth even slightly and you change the adult form
changes can also alter the timing of developmental events like the sequence in
which different body parts start and stop developing.