The Geological Time Scale

What is the Geologic Time Scale?

• We divide time in to different units depending on how long a time frame we are looking at

  • We don't calculate a road trip in seconds, or how long it took to build a skyscraper in minutes

• When we look at very long periods of time like the history of Earth, we need large units to reflect that

Grade 8 Ohio | Lesson 6.4 & 6.5

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.

  • Inference are made on the principle of uniformitarianism

    • processes operate today also operated in the past

      • Example: Gravity always existed

Grade 8 Ohio | Lesson 6.4 & 6.5

What is the Geologic Time Scale?

• The Geologic timescale was first developed comparing index fossil world wide

  • allowed scientists to set a relative age of rocks

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

Grade 8 Ohio | Lesson 6.4 & 6.5

Dividing Geologic Time

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

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

Grade 8 Ohio | Lesson 6.4 & 6.5

Precambrian Time

• The beginning of Geologic time

• ~88% of Earth's History

• Ended 542 million years ago (MYA)

• Few Fossils survive

Grade 8 Ohio | Lesson 6.4 & 6.5

Eras

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

  • Paleozoic

  • Mesozoic

  • Cenozoic

Grade 8 Ohio | Lesson 6.4 & 6.5

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 ​

Placeholder

and geologic events.

Drag these tiles and drop them in the correct blank above

life forms

rocks

plants

volcanoes

places

The Formation of the Earth

• The oldest rocks on Earth have been found to be 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

Grade 8 Ohio | Lesson 6.4 & 6.5

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

Grade 8 Ohio | Lesson 6.4 & 6.5

The Second Atmosphere

• Two things formed the Earths 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, and other trace gases

Grade 8 Ohio | Lesson 6.4 & 6.5

The Oceans & Continents

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

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

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

Grade 8 Ohio | Lesson 6.4 & 6.5

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

Grade 8 Ohio | Lesson 6.4 & 6.5

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

Dropdown

Early lifeforms preformed Photosynthesis Which released ​

Select answer

into the second atmosphere

Multiple Choice

What Eon, Era, Period and Epoch are you living in today?

• Phanerozoic, Cenozoic, Quaternary, Holocene

• Triassic, Jurassic, and Cretaceous

• The Cambrian period

Describing Geologic Change

You have likely changed a lot since you were born. Just imagine all of the changes the Earth has been through since it formed 4.6 bya!

Timelines

Timelines are a tool that can show the relative order in which these events happened, from the earliest to the most recent. Ands it can tell us the actual, or absolute date when each occurred.

Geologic Timeline

Learning about events and when they happened helps us piece together our biological history. We can see connections and major progressions in evolution and biodiversity.

Multiple Choice

The geologic time scale is divided into units of time based on what?

• a specific amount of time

• the evolution of humans

• major or catastrophic events

• no one knows

Multiple Choice

Who is the Greek god of the Underworld?

• Zeus

• Hades

• Poseidon

• Athena

Multiple Choice

Check for comprehension: Which Eon marked the first oxygen and life forms on the Earth

• Hadean

• Archean

• Proterozoic

Multiple Choice

What is the supercontinent proposed by Wegener from last time?

• Laurasia

• Gondwanaland

• Pangaea

• Rodinia

Multiple Choice

What period marked the first vertebrates?

• Cambrian

• Ordovician

• Mississipian

• Permian

Multiple Choice

What period marked the first mass extinction?

• Cambrian

• Ordovician

• Mississipian

• Permian

Multiple Choice

What period marked the first mammals?

• Jurassic

• Triassic

• Cretaceous

Multiple Choice

What period marked the first birds?

• Jurassic

• Triassic

• Cretaceous

Multiple Choice

What period marked the fourth mass extinction?

• Jurassic

• Triassic

• Cretaceous

Multiple Choice

What epoch marked the first primates?

• Paleogene

• Neogene

• Quaternary

Multiple Choice

What period marks the present?

• Paleogene

• Neogene

• Quaternary

Poll

What time period interested you the most?

• Precambrian

• Paleozoic

• Mesozoic

• Cenozoic