© Fall 2005, Pflugerville ISD, 8th Grade 8th Grade Science.

© Fall 2005, Pflugerville ISD, 8th Grade

8th Grade Science

Unit 4 : Chapter 16 © Fall 2005, Pflugerville ISD, 8th Grade

Chapter 16- The Rock & Fossil Record

Section 1: Earth’s Story & Those Who First Listened

Section 2: When on Earth?

Section 3: Looking at Fossils

Section 4: Time Marches On

Unit 4 : Chapter 16 : Section 1© Fall 2005, Pflugerville ISD, 8th Grade

“The present is the key to the past.”-James Hutton

We study the past because if we don’t, we are doomed to repeat it. But how can studying the

present help us understand earth’s history?What are some processes you can see today that

also occurred millions of years ago?

What Do You Think?


Earth’s Story & Those Who Listened

James Hutton 1726-1797

•“The present is the key to the past.”

•Father of modern geology



Hadrian’s Wall, England

•Hutton knew that Hadrian’s wall was built by the Romans in historical times



Hadrian’s Wall, England

•Only 1600 years old, the wall was already starting to weather and erode



Arthur’s Seat Volcano, Edinburgh, Scotland

•Hutton wondered how long it would take to erode a mountain




•Hutton decided that it would take millions of years, making the earth very ancient




•Hutton realized that erosion and deposition have been going on for a long time




•Uniformitarianism is Hutton’s belief that geologic processes are uniform and do not change over time




•Hutton’s views of a billion-year-old earth clashed with most scientists’ belief in catastrophism



•Most scientists supported catastrophism, the idea that all geologic change happens quickly



•These scientists used huge floods, eruptions and catastrophes to explain rapid geologic change



•Today, scientists think that sudden events are the cause of some changes in earth’s past



•But they agree that the earth is billions of years old, and that most change is gradual


When on Earth?

Suppose your friend piles his stuff on his floor and never cleans his room. Under the top layer of

clothes, you find a pizza box. Under this is a bunch of CDs then some homework and under this is a ham

sandwich.Arrange these four layers from oldest to youngest…

What Do You Think?


When on Earth?

Grand Canyon

•The Principle of Superposition states that younger rocks lie over older rocks


When on Earth?

Grand Canyon

•The Principle of Superposition is used to find the relative ages of rock layers


When on Earth?

•The Law of Cross-Cutting Relationships can tell geologists the relative age of a fault or intrusion


When on Earth?

•The dike is the youngest feature, because the other layers were cut by it


Relative Dating

•Use your knowledge to order the layers, faults and intrusions in the next slide from oldest to youngest


Relative Dating


Relative Dating


•Geologists can use rock layers from many locations to create a geologic column


Relative Dating


Relative Dating

•The geologic column is an ideal sequence of rock layers that contains all known rock formations and fossils on Earth


When on Earth?

Hutton’s Unconformity

•An unconformity is a surface that represents a missing part of the geologic column


Formation of an Unconformity

30-15 Million Years Ago

•Sediment is eroded from a hill and deposited in a valley



15-5 Million Years Ago

•The area is uplifted and exposed to erosion, then the land surface is eroded away



5 Million Years Ago- Present

•Deposition resumes

•Can you spot the unconformity?


Absolute Dating

•When animals eat, they ingest radioactive Carbon-14


Absolute Dating

Carbon-14 decays into Nitrogen-14

Carbon-14 Nitrogen-14


Absolute Dating

•By comparing the amount of C-14 to N-14, geologists can calculate the age of a fossil


Absolute Dating

•Since C-14 has a half-life of only 5730 years, other isotopes are used to date older rocks


Absolute Dating


•The oldest rocks on Earth have been dated to 4.5 billion years, confirming Hutton’s beliefs


Looking at Fossils

Imagine that a geologist 65 million years from now has unearthed fossils of your life.

What would she find?

What Do You Think?


Looking at Fossils

Saber-Tooth Cat Fossil

•A fossil is the remains or physical evidence of an organism preserved by geologic processes


Looking at Fossils

Fossil Amber with Insect Inclusions

•Fossilized tree sap is called amber


Looking at Fossils

Fossil Amber with Insect Inclusions

•Animals caught in amber are perfectly preserved


Looking at Fossils

Woolly Mammoth

•Fossils of mammoths, extinct for 12,000 years, have been found frozen in Arctic ice


Looking at Fossils

Theropod Track

•A trace fossil is naturally preserved evidence of animal activity


Looking at Fossils

Theropod Track

•This dinosaur track is located in Glen Rose, Texas, in Dinosaur Valley State Park


Looking at Fossils

Ammonite Fossil

•A mold is a cavity in rock where a plant or animal was buried


Looking at Fossils

Ammonite Fossil

•A cast is an object made when sediment fills a mold and becomes rock


Looking at Fossils


Looking at Fossils

Ammonite Fossil

•Which of these is the mold and which is the cast?


Looking at Fossils

Whale Bones

•Most animals are not buried fast enough to form fossils


Looking at Fossils

Whale Bones

•These whale bones will be broken down before they can form fossils


Looking at Fossils

Trilobite Fossil

•The trilobite Phacops lived for a short time 400 million years ago


Looking at Fossils

Trilobite Fossil

•An index fossil is one found for a short time in rock layers around the world


Looking at Fossils

Trilobite Fossil

•If Phacops is found in a rock layer, the rock must be about 400 million years old


Time Marches On

If the history of Earth were the length of one calendar year, on what date do you

think modern humans arrived?

What Do You Think?


Time Marches On

Humans First Arrived

•Humans evolved in the last half-hour of New Years Eve!


Time Marches On

•The Geologic Time Scale divides Earth’s history into eons, eras, & periods


Time Marches On

•Since most fossils are from the Phanerozoic Eon, this is the eon that is given the most attention


Time Marches On

•The Phanerozoic is actually the shortest of the four eons


Time Marches On

Paleozoic Era 540-248 mya

•In the Paleozoic Era, life in the oceans, as well as all major plant groups, flourished


Time Marches On

Mesozoic Era 248-65 mya

•With a mass extinction at the end of the Paleozoic, the remaining reptiles thrived


Time Marches On

Mesozoic Era 248-65 mya

•Known as the Age of Reptiles, birds and small mammals appeared late in the Mesozoic


Time Marches On

Cenozoic Era 65 mya- Present

•Mammals flourished after a mass extinction killed the dinosaurs


Time Marches On

Cenozoic Era 65 mya- Present

•The Cenozoic is known as the Age of Mammals

Unit 4 : Chapter 16© Fall 2005, Pflugerville ISD, 8th Grade

Let’s Review!

- 1 -

What did James Hutton mean by the comment,

“The present is the key to the past”?


Let’s Review!

- 2 -

How can you tell the age of rocks and fossils?


Let’s Review!

- 3 -

How is a fossil created?Describe how a geologist

would use an index fossil…


Let’s Review!

- 4 -What type of event ended

both the Paleozoic and Mesozoic Eras?

What geologic time period was occurring 200 million

years ago?


http://members.aol.com/DarqDean/leftfield/offossil.html.


Pre-AP Extensions

© Fall 2005, Pflugerville ISD, 8th Grade 8th Grade Science.

Documents

Transcript of © Fall 2005, Pflugerville ISD, 8th Grade 8th Grade Science.