Relative Dating and Index Fossils

​Science Root of the Day:

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Unit 4 Section 5: The Geologic Time Scale & Early Earth

Multiple Choice

True or False: All plants and animals contain carbon

• True

• False

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​ ​

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is a method of determining the absolute ages of rocks

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Radioactive dating

relative dating

index fossils

plate tectonics

Reorder

Based on the law of superposition, what is the order of these rock layers, from oldest to youngest?

• 4

• 3

• 2

• 1

1

2

3

4

• 1
• 2
• 3
• 4

Multiple Choice

A fossil known to have lived in a particular geologic age that can be used to date the rock layer in which it is found

• Index Fossil

• Uncomformity

• Disturbed Fossil

• Intrusion

Lesson Objectives

• Understand How Scientists divide up Earth's History into a geologic timescale

• Identify the reason for using a geologic time scale to observe changes in the Earth

• Describe How Earth Developed during Precambrian Time?

What is the Geologic Time Scale?

• The Geologic Time Scale: A record of the geologic events and the evolution of life forms as shown in the fossil record.

  • Inferences are made based on the principle of uniformitarianism

    • processes that operate today also operated in the past

      • Example: Gravity always existed

History of the Geologic Time Scale

• The Geologic time scale was first developed by comparing index fossils worldwide

  • allowed scientists to set a relative age of rocks

  • radioactive dating later helped to get more exact ages in some instances

Dividing Geologic Time

• In the fossil record, scientists found major changes in lifeforms happening at certain times

  • When new life appears and other life becomes extinct

• These changes are used to set beginning and end points for certain times

Precambrian Time

• The beginning of Geologic time

• ~88% of Earth's History

• Ended 542 million years ago (MYA)

• Few Fossils survive

Eras

• We Divide all time after the Precambrian time into three large periods of time known as Eras

  • Paleozoic

  • Mesozoic

  • Cenozoic

Periods

• Period: A unit of geologic time that is part of an era

  • Example: The Mesozoic era is made up of three periods

    • Triassic

    • Jurassic

    • Cretaceous

  • Named for areas where rocks and fossils from that period were first described

Grade 8 Ohio | Lesson 6.4 & 6.5

Drag and Drop

The Geologic time scale is a record of ​

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and geologic events.

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life forms

rocks

plants

volcanoes

places

Multiple Choice

Scientists chose where units of geologic time began and ended based on the appearance or disappearance of life.

• true

• false

Multiple Choice

Using the geologic timeline, about how old was the Silurian Period?

• 542 million

• 199 million

• 420 million

• 40 million

The Formation of the Earth's Layers

• The Earth Began as a ball of dust, rock, & ice in space pulled together by gravity

  • As it got bigger, the force of gravity increased and pulled more into it

• The energy from those collisions increased the temperature of the materials and melted them into the layers of the Earth

The Formation of the Earth's Rocks

• The oldest rocks on Earth are 4 billion years old, but Earth was formed before that

• Earth collided with something else in space

  • One piece broke off and formed the moon at the same time

• Analyzing Earth and moon Rocks show both to be about 4.6 Billion Years Old

The First Atmosphere

• Early Earth was made up of gases like hydrogen and helium

  • Not conducive to life

  • Solar flares from the sun destroyed the first atmosphere

The Second Atmosphere

• Two things formed the Earth's 2nd atmosphere which contains

  • Volcanic Eruptions

  • Collisions with comets

    • Comet: A ball of dust & ice that orbits the sun

• The second atmosphere contains

  • Carbon dioxide,

  • Oxygen

  • Nitrogen

  • Other trace gases

The Oceans & Continents

• When the Earth first formed, it was too hot for water to remain in the liquid state

• As the Earth cooled, water condensed to form the oceans

• The cooling also allowed rocks to harden and form the tectonic plates

Early Organisms

• The exact beginning of life is unknown

  • Fossils show single-celled organisms lived 3.5 billion years ago, and all other life evolved from them

• Early lifeforms received energy from the sun through photosynthesis, which released Oxygen into the atmosphere

  • Some Oxygen bonded to create Ozone, which blocks out Ultraviolet waves

Multiple Choice

Earth Formed approximately _____ billion Years ago

• 4.6

• 1000

• 400

• 3.5

Multiple Choice

The first life on Earth appeared approximately _____ billion Years ago

• 4.6

• 1000

• 400

• 3.5

Multiple Choice

Which of the following is not a part of Earth's second atmosphere

• helium

• oxygen

• water vapor

• carbon dioxide

Dropdown

Early lifeforms preformed Photosynthesis Which released ​

Select answer

into the second atmosphere