Clues to Earths Past
Chapter 12
Fossils
Section 12.1
Fossil Formation
What are Fossils?
Fossil Formation
Fossil Evidence of once living organisms preserved in rocks
Remains
Imprints
traces
Fossil Formation
What are the conditions necessary to form fossils?
Fossil Formation
Necessary Conditions to from Fossils:
Body protected from scavengers and decay buried quickly
Hard parts
Fossil Formation
List some types of fossils.
Fossil Formation
Types of fossils:
Petrified remains petrified forest organism replaced by minerals one molecule at a time
Carbonaceous films gases and liquids forced from body leaving carbon
Original remains real organism left
Trace fossils foot prints
Molds and casts
Fossil Formation
Describe the difference in how a mold and cast are formed.
Fossil Formation
Mold
Organism buried
Organism is dissolved
Mold in the cavity left behind
Fossil Formation
Cast
Mold is filled with rock solution or sediment and hardens
Cast has same shape as original organism
Index Fossil
What is an Index Fossil?
Index Fossil
What is an index fossil?
Index Fossil
Existed on Earth for relatively short period of time
Abundant
Widespread geographically
Index Fossils can be used to date rock layers.
Fossils and Ancient Environments
Fossils can tell what the environment was like.
Water land
Warm cold
Extinction of Dinosaurs
Section 12.2
What Killed the Dinosaurs?
Dinosaurs were the dominant species for 160 million years.
Dinosaurs became extinct 66 million years ago.
What Killed the Dinosaurs?
Two Theories:
Meteorites
Collisions changed atmosphere
Evidence iridium layer
Volcanoes
Changed atmosphere
Iridium layer
Relative Ages of Rocks
Section 12.3
The Principle of Superposition
What is the Principle of Superposition?
The Principle of Superposition
In an undisturbed layer of rock, the oldest rocks are on the bottom and the rocks become progressively
younger toward the top.
Principle of Cross-cutting Relations
What is Cross-cutting Relations?
Principle of Cross-cutting Relations
Igneous intrusions which cut across rock layers are younger than the rock layers.
Principle of Inclusive Fossils
What is the Principle of Inclusive fossils?
Principle of Inclusive Fossils
Fossils found in rock layers must be older than the rock layers.
Relative Dating
What is Relative Dating?
Relative Dating
Determine which rock layer is older.
Unconformities
Distinguish between
Angular unconformities
Disconformity
Nonconformity
Unconformities
Angular Unconformities
Rock layers laid down
Layers tilted
Layers eroded
Unconformities
Disconformity
Rock layers laid down
Rock layers eroded
Missing layers
Unconformities
Nonconformity
Igneous or Metamorphic rocks are eroded
Sedimentary rocks are laid down
Missing igneous or metamorphic rocks
Correlating Rock Layers
Similar minerals
Fossils
Order of layers
Absolute Ages of Rocks
Section 12.4
Absolute Dating
What is Absolute Dating?
Absolute Dating
Determine the age, in years, of rock or other objects
Radioactive Decay
Describe Radioactive Decay.
Radioactive Decay
1 neutron = 1 proton + 1 beta(electron)
New element is formed with more protons.
Radioactive Decay
What is half-life?
Radioactive Decay
Half-life time for half of a radioactive isotope to decay.
Example: carbon-14 half-life = 5730 years
Radiometric Dating
Process of measuring the amount of parent and daughter materials in a rock and by knowing the half-life
of the parent, determining the age of the rock.
Radiometric Dating
Radiocarbon Dating
Useful to 50,000 years
Carbon-14 decays to Nitrogen-14 at a steady rate after an organism dies
Principle of Uniformitarianism
What is the Principle of Uniformitarianism?
Principle of Uniformitarianism
James Hutton
Earth processes occurring today are similar to those that occurred in the past.
