Outline for Chapter 4 Views of Earth’s past
1. Earth’s past is revealed in rocks and fossils (4.1)
A. Rocks, fossils and original remains give clues about the past
Fossils are traces or remains of living things from long ago
Most fossils are hardened animal remains such as bones and teeth
1.
Original Remains – are the actual body parts of an organism
Decomposition does not take place
Give evidence of how life was long ago
a. Ice – preserves organisms
b. Amber – a natural substance from trees
only preserves small organisms
2.
3.
c. Tar – a thick oily liquid
Fossil Formation
a. Fossils form in sedimentary rocks
b. Conditions must be just right for fossils to form
c. Heat and pressure can destroy fossils
Fossils in Rocks
Some fossils are traces of animals not actual animal parts
a. Molds and Casts
Mold is a visible shape of an animal
Cast is the imprint or impression of an animal
b. Petrified Wood – minerals replace tree parts
c. Carbon Films – stamped impression of an organism carbon is the ink
d. Trace Fossils – footprints, feces, or other traces of organisms
B. Fossils and other natural evidence show changes in life and the environment
Scientists study fossils to learn about the life and environment in the past
Fossils show the disappearance of many species
1.
Tree Rings –show tree growth and age
a. Thicker rings show more growth
b. Help scientists understand weather patterns in the past
2.
Ice Cores – a tubular sample of the layers of snow and ice that has built up over years
a. Help scientists understand climate and how it has changed
b. A vertical timeline of Earth’s past
2. Rocks provide a timeline for Earth (4.2)
A. Layers of sedimentary rocks show relative age
Relative Age is the age of an object or event in relation to other events or objects around it
Sedimentary rock layers contain information about Earth’s past, older layers are at the bottom
Younger layers are at the top
1.
Igneous Rock and Sedimentary Layers
a. Igneous rock is younger than the sedimentary rock layers it cuts through
b. What happens to any fossils when the lava flows through the rock layers?
2. Index Fossils – are fossils of organisms that lived in many places and only during a
specific time period
a. An organism that was fossilized in rock must have lived during the same time the
rock was formed
b. Index fossils can be used to date other fossils by looking at the locations in the layers
c. Study the image below to learn how index fossils help determine ages of rocks
B. Radioactive dating can show absolute age
Absolute age is the actual age of an event or object.
3.
4.
Half-Life
a. The length of time it takes for half of the atoms in a sample of a radioactive element
to change from an unstable form to another form
Using Absolute and Relative age
a. Radioactive dating of igneous rocks shows absolute age
b. Layers of sedimentary rock shows a relative order of events
c. Fossils help determine the sequence of events in sedimentary rock
Where is the igneous rock layer?
Why is it the youngest?
Using the Nerinea trinodosa as an index fossil, determine the approximate age of fossil C.