1. 14.1 Section Objectives – page 369
Identify the different types of fossils and how they are formed
Summarize the major events of the geologic time scale.
14.1 Section Objectives – page 369

2. When was Earth formed?
The earth was formed 4.6 billion years ago when scientists believed that meteorites constantly bombarded the Earth’s surface.

3. Section 14.1 Summary – pages 369-379
Early History of Earth
What was early Earth like? Some scientists suggest that it was probably very hot. The energy from colliding meteorites could have heated its surface.
Early Earth’s atmosphere contained water vapor, sulfur dioxide, carbon monoxide, carbon dioxide, ammonia and methane.
Section 14.1 Summary – pages

4. Section 14.1 Summary – pages 369-379
Early History of Earth
About 4.4 billion years ago, Earth might have cooled enough for the water in its atmosphere to condense. This might have led to millions of years of rainstorms with lightning.
Section 14.1 Summary – pages

5. Section 14.1 Summary – pages 369-379
History in Rocks
There is no direct evidence of the earliest years of Earth’s history. The oldest rocks that have been found on Earth formed about 3.9 billion years ago.
Important in discovering the diversity of life.
Section 14.1 Summary – pages

6. When did life begin? 3.5 billion years ago there was life on Earth.
Earliest known life were prokaryotes.
How do we know this?

7. Section 14.1 Summary – pages 369-379
Fossils-Clues to the past
Types of Fossils
A fossil is evidence of an organism that lived long ago that is preserved in Earth’s rocks.
Fossils Types
Formation
A trace fossil is any indirect evidence
A trace fossil is any indirect evidence
Trace fossils
left by an animal and may include a
footprint, a trail, or a burrow.
When minerals in rocks fill a space
Casts
left by a decayed organism, they make
a replica, or cast, of the organism.
A mold forms when an organism is
A mold forms when an organism is
Molds
buried in sediment and then decays,
leaving an empty space.
Petrified/
Petrified-minerals sometimes penetrate
and replace the hard parts of an
Permineralized
organism. Permineralized-void spaces
fossils
in original organism infilled by
minerals.
Amber-
At times, an entire organism was
Preserved or
quickly trapped in ice or tree sap that
frozen fossils
hardened into amber.
Section 14.1 Summary – pages

8. Section 14.1 Summary – pages 369-379
Fossils-Clues to the past
About 95 percent of the species that have existed are extinct—they no longer live on Earth.
Among other techniques, scientists study fossils to learn about ancient species.
Section 14.1 Summary – pages

9. Section 14.1 Summary – pages 369-379
Paleontologists-Detectives to the past
Paleontologists, scientists who study ancient life, try to solve the mystery of what happened.
They use fossils to determine the kinds of organisms that lived during the past and sometimes to learn about their behavior.
Section 14.1 Summary – pages

10. Section 14.1 Summary – pages 369-379
Paleontologists-Detectives to the past
Paleontologists also study fossils to gain knowledge about ancient climate and geography.
By studying the condition, position, and location of rocks and fossils, geologists and paleontologists can make deductions about the geography of past environments.
Section 14.1 Summary – pages

11. Section 14.1 Summary – pages 369-379
Fossil formation
For fossils to form, organisms usually have to be buried in mud, sand, or clay soon after they die.
Most fossils are found in sedimentary rocks. These rocks form at relatively low temperatures and pressures that may prevent damage to the organism.
Section 14.1 Summary – pages

12. Section 14.1 Summary – pages 369-379
Fossil formation
Fossils are not usually found in other types of rock because of the ways those rocks form. For example, the conditions under which metamorphic rocks form often destroy any fossils that were in the original sedimentary rock.
Section 14.1 Summary – pages

13. Section 14.1 Summary – pages 369-379
The Fossilization Process
Few organisms become fossilized because, without burial, bacteria and fungi immediately decompose their dead bodies.
Fossilization takes many years.
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14. Section 14.1 Summary – pages 369-379
The Fossilization Process
A Protoceratops drinking at a river falls into the water and drowns
Sediments from upstream rapidly cover the body, slowing its decomposition. Minerals from the sediments seep into the body.
Over time, additional layers of sediment compress the sediments around the body, forming rock. Minerals eventually replace all the body’s bone material.
Earth movements or erosion may expose the fossil millions of years after it formed.
Section 14.1 Summary – pages

15. Determining Age of Fossils
Relative Dating (time period)
Layers at the surface are younger than deeper layers.
Can determine relative age and order of appearance of species.

16. Determining Age of Fossils
Radiometric Dating (specific age)
Use radioactive isotopes in rocks.
Radioactive isotopes decay over time and form new isotopes.
Each isotope has a specific decay rate and thus scientists can determine the age of rocks.