THE FOSSIL RECORD

Chapter 5

OBJECTIVES SPI 0807.5.5 Compare fossils found in

sedimentary rock to determine their relative age.

I can: Compare fossils found in sedimentary

rock to determine their relative age. Identify types of fossils. Explain how fossils are used to interpret

the past. Explain the geologic time scale.

GEOLOGIC HISTORY1. Uniformitarianism: geologic change

happen through slow gradual processes.

Most geologic change

2. Catastrophism: geologic change occurs suddenly by catastrophes.

Asteroid, comets, earthquakes, volcanoes

I can explain how fossils are used to interpret the past.

RELATIVE AGE (#77) Examines the position within rock layers

to estimate the age of an object.Look for key words such as before, after,

older, youngerExamples:

Before the dinosaurs existed Older than my brother After the extinction of the dinosaurs

Bottom layers: oldest Top layers: youngest

I can compare fossils found in sedimentary rock to determine their relative age.

ABSOLUTE AGE Precisely measures the age of fossils or

rocks in years.Examples:

5780 years ago Born in 1900 At the beginning of the Triassic period

I can compare fossils found in sedimentary rock to determine their relative age.

TYPES OF FOSSILS Fossil (#36): Remains

or physical evidence of an organism preserved by geologic processes.

1. Fossils in rock: formed when organism dies and quickly covered by sediment.

Hard parts of the organism are preserved

Soft parts decayI can identify types of fossils.

TYPES OF FOSSILS2. Fossils in

amber: entire organisms preserved inside hardened tree sap.

Insect gets caught in sticky sap, and then hardens.

Some of the best fossils.

I can identify types of fossils.

TYPES OF FOSSILS3. Petrification:

minerals replace the organism’s tissues.

I can identify types of fossils.

TYPES OF FOSSILS4. Fossils in asphalt

Thick, sticky pools trap and preserve organisms.

The La Brea asphalt deposits in Los Angeles, California have preserved organisms for at least 38,000 years.

I can identify types of fossils.

TYPES OF FOSSILS5. Frozen Fossils

In 1999, scientists removed a 20,000-year-old woolly mammoth that was frozen in the Siberian tundra.

These mammoths became extinct about 10,000 years ago.

Because cold temperatures slow down decay, the mammoth was almost perfectly preserved.

I can identify types of fossils.

TYPES OF TRACE FOSSILSTrace fossils: naturally preserved evidence of animal activity.

Tracks Reveal size and

speed of an animal. Burrows

Preserved shelters. Coprolite

Preserved animal dung.I can identify types of

fossils.

TYPES OF TRACE FOSSILS Molds: a cavity

in rock where an organism was buriedSunk in/hole

Cast: created when sediment fills a mold and becomes rock.Raised up

I can identify types of fossils.

INDEX FOSSILS Index fossils

(#44): fossils of organisms that lived for a relatively short, well-defined geologic time span.

AmmonitesMarine mollusks

similar to modern squid.

Lived b/t 230 million and 208 million years ago

I can identify types of fossils.

INDEX FOSSILS Trilobites

Closest living relative is the horseshoe crab

Lived about 400 million years ago

When scientists find fossils of trilobites anywhere on Earth, they assume the rock layers are also approximately 400 million years oldI can identify types of

fossils.

USING FOSSILS TO INTERPRET THE PAST Gives a rough sketch of the history of

life on Earth. Organisms with hard body parts have

left more fossils. Organisms that lived in areas that

favored fossilization have left more fossils.

I can explain how fossils are used to interpret the past.

USING FOSSILS TO INTERPRET THE PAST Show a history of environmental

change.Marine fossils found on mountaintops in

Canada means that these mountains formed at the bottom of the ocean.

Detect the presence of ancient seasReconstruct ancient coastlinesReconstruct past climates

Determine relationships and similarities between fossils

I can explain how fossils are used to interpret the past.

GEOLOGIC TIME Earth is about

4.6 billion years old.

The Grand CanyonColorado River

has cut/eroded away nearly 2 km deep in some places.

Represent almost half, nearly 2 billion years, of Earth’s history.

I can explain the geologic time scale.

GEOLOGIC TIME SCALE Geologists divided Earth’s history into a

scale with distinct sections of time.1. Eons: largest division of geologic time

Four eons: Hadean, Archean, Proterozoic, Phanerozoic

2. Eras: 2nd largest division of geologic time3. Periods: 3rd largest division of geologic

time4. Epochs: 4th largest division of geologic

timeI can explain the geologic time scale.

I can explain the geologic time scale.

PHANEROZOIC ERA1. Paleozoic Era (Old Life)

Marine life flourished, few land animals Land plants appeared By the end of the era, amphibians and reptiles

lived on the land. Ended with the largest mass extinction(#33) in

history 90% of all species became extinct

I can explain the geologic time scale.

MESOZOIC ERA2. Mesozoic Era (Age of Reptiles)

Dinosaurs dominated the landSmall mammalsBirdsEnded with a mass extinction15-20% of all species became extinctPossibly caused by global climate change

I can explain the geologic time scale.

CENOZOIC ERA3. Cenozoic era (Age

of Mammals) Mammals flourished Adaptations may

have helped them survive the extinction of the dinosaurs caused by environmental changes.

Regulate internal body temperature

Develop young inside the mother

I can explain the geologic time scale.