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Earth's History and Geologic Time
Define
 Geologic time scale; a record of Earth's history from its origin of 4.6 billion years
ago (bya) to present
 - Cyanobacteria; blue-green algae earliest form of life; contain chlorophyll and
used photosynthesis (produce oxygen) created gas in the atmospheric that
allowed single-celled organisms to develop into more complex organisms
 Index fossil easily recognized, abundant, and widely distributed geographically
 Homo sapiens the species of humans
 Principle of superposition if rocks are left undisturbed the oldest layers will
remain on the bottom, newest layers on top
- Angiosperms- plants that produce seeds.
 Relative age dating gives scientists a clearer understanding about geologic events
in Earth's history
 Natural selection Charles Darwin's idea of traits changing over time
 Eon the largest of these time units
Radioactive decay the emission of radioactive particles and the resulting change
into the other isotopes over time is called radioactive decay
 Era usually tens to hundreds of millions of years in duration
 -Paleontologist Scientist that Studies fossils
 Period generally tens of millions of years in duration, though some periods of the
Precambrian are considerably longer
 -Absolute age enables scientists to determine the numerical age of rocks and
other objects
 Epoch generally hundreds of thousands to millions of years in duration
 -Radiometric dating when scientists date an object using radioactive isotopes,
they are using a method called radioactive dating
 Half life scientists measure the length of time it takes for one-half of the
original parent isotope to decay, called its half-life
1. If the same type of fossils are found in two separate rock layers, it's likely that the
two rock layers _______________.
Moved from a fault, have the same fossils, are called an index fossil
2. Name two sources of Earth's internal energy.
Radioactive decay, gravity, solar energy
3. Describe the major reason why scientists think the dinosaurs went extinct.
Asteroid hit the earthchange atmosphereplants dieanimals died Pleistocene Ice age
4. How did cyanobacteria help increase the amount of oxygen in the atmosphere?
Photosynthesis, released gas into the atmosphere as a byproduct.
5. The development of ________ helped to promote the development of complex
organisms. The atmosphere
6. When did the Earth form?
4.6 billion years ago
7. List the order of the four Eras we described from longest ago to present day.
Eon, Era, period, Epoch
8. Describe the life forms in the Precambrian, Paleozoic, Mesozoic and Cenozoic Eras.
Precambrian era( ch 22)- trilobites, cyanobacteria, early invertebrates (soft bodies-partial or trace
fossils), some jellyfish
Paleozoic era (ch 23 section 1)- 544mya SHELLS, Trilobites (early), Invertebrates & Vertibrates
(backbone animals)- fishlike without jaws (Devonian: forests, vertebrates form to land), fish that lay
egs, amphibians
-appalachian Mountains form during this time (mountain building time) Pennsylvanian epoch
End of this Era 90% of marine species, 70% land species died off (climate changed, lower sea level)
Pangea formed at the end of the Permian period—marine organisms couldn’t adapt to changes
extinct
Mesozoic Era-(Ch 23 section 2) Pangea breaks up, reptiles (able to survive because skin and egg
laying) spread Triassic period: Dinosaurs evolved and other species became extinctPaleontologists calculate how quickly they travel through their footprints, (as fast as a modern race
horse) maybe dinos were warm blooded
Birds- juarassic period: maybe became small meat eaters
Mammals- Triassic period; first mouse-like creature hair and milk producing for the young
Gymnosperms- plants that produced flowers and seeds (pines and ginkgo trees)
Angiospers- flowereing plants Mesozoic era= magnolia and oak trees
Extinction: comet or asteroid collided with earthsmokeblock out sun plants die animals die,
some species survived (ancestors are alive today)
Cenozoic Life-(chapter 23-3) ice age, age of mammals, homo sapiens, primates, forests,
9. After cyanobacteria started to increase the amount of oxygen in the atmosphere and
the ozone layer started to develop what could start to develop as well?
New types of species and complex celled organisms
10. How did the Paleozoic Era end?
Extinction (ice age) Pangea, a majoring of animals and plants died out
11. How old is a mammoth's tusk if 25% of the original C-14 remains in the sample?
The half life of C-14 if 5,730 years. Extra credit
What is the order of rock from oldest to youngest? C, B, A, D, E
13. Give an example of a trace fossil.
a dinosaur fossil, impression of a shell etc.
14. Describe what each era looked like.
Written response: You must describe how relative and absolute age differ. Describe how
scientist use them to establish the ages of rock layers using words like “compares”,
“approximate” and “exact”.