Transcript Section 1 Notes

Chapter 17 Section 1
paleontologists- scientists who study fossils
-they infer what past life forms were like
-arrange fossils according to time in which they
lived
-all this info together is the fossil record
fossil record- provides evidence of history of
past life on Earth, shows how different
organisms change and evolve over time
-about 99% of all species that have ever lived on
Earth have become extinct
How Fossils Form
-fossils can be bones, eggs, footprints, animal
droppings, shells, pollen
-many fossils form in sedimentary rock
**List the three steps of fossil formation (page
418)
Interpreting Fossil Evidence-Two Techniques:
1) Relative Dating
-age of fossil is determined by comparing its
placement with that of fossils in other layers
of rock
-layers of sedimentary rock form in order by age
-also use index fossils- distinctive fossil used to
compare the relative age of fossils
-relative dating allows paleontologists to
estimate a fossil’s age compared to other
fossils, but no info on absolute age or age in
years
2) Radioactive Dating
-used to assign absolute age to fossils
-age is calculated based on amount of radioactive
isotopes a fossil contains
-uses half-life to determine age
half-life- length of time required for half of the
radioactive atoms in a sample to decay
Geologic Time Scale
-used to measure evolutionary time
-major changes in fossil animal and plants are
used to mark where one segment ends and
another begins
-after Pre-Cambrian Time, the basic divisions are
eras and periods
Eras
Pre-Cambrian Time (oldest), Paleozoic,
Mesozoic and Cenozoic (most recent)
Periods
Vendian, Cambrian, Ordovician, Silurian,
Devonian, Carboniferous, Permian, Triassic,
Jurassic, Cretaceous, Tertiary, Quaternary