Geologic Time Scale: Eons, Eras, Periods, Epochs

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Questions and Answers

Why was the evolution of breathing a crucial step for animals colonizing land?

  • It allowed them to develop waxy leaves and leathery skin.
  • It provided the necessary physiological adaptation for terrestrial life. (correct)
  • It enabled them to reproduce on dry land without returning to water.
  • It facilitated the formation of supercontinents like Pangea.

During which period did the first reptiles evolve, marking a significant step in terrestrial adaptation?

  • Cretaceous Period
  • Carboniferous Period (correct)
  • Jurassic Period
  • Triassic Period

What major geological event characterized the Permian Period?

  • The formation of the supercontinent Pangea. (correct)
  • The peak of dinosaur size and distribution.
  • The appearance of the first flowering plants.
  • The initial separation of Laurasia and Gondwanaland.

Which of the following represents the correct order of geologic time intervals, from longest to shortest?

<p>Eons → Eras → Periods → Epochs (D)</p> Signup and view all the answers

Which of the following adaptations was crucial for plants and animals to survive the dry climate of the Permian Period?

<p>Development of waxy leaves or leathery skin. (C)</p> Signup and view all the answers

The Precambrian Supereon encompasses approximately what percentage of Earth's total geologic history?

<p>90% (D)</p> Signup and view all the answers

What is the significance of the Permian Extinction?

<p>It was the largest mass extinction event in Earth's history. (C)</p> Signup and view all the answers

During which era did dinosaurs diversify and dominate terrestrial ecosystems?

<p>Mesozoic Era (D)</p> Signup and view all the answers

Which of the following characterizations best describes the conditions prevalent on Earth during the Hadean Eon?

<p>Characterized by hellish conditions and the absence of complex life. (C)</p> Signup and view all the answers

What evolutionary milestone occurred during the Jurassic Period?

<p>The earliest birds evolved from reptile ancestors. (B)</p> Signup and view all the answers

If a geologist is studying a rock layer dated to 600 Ma, to which eon does this rock layer belong?

<p>Proterozoic Eon (B)</p> Signup and view all the answers

Which of the following Eons from the geologic time scale is the oldest?

<p>Hadean (A)</p> Signup and view all the answers

Which geological period is characterized by the continents being close to their present-day locations and ending with the extinction of the dinosaurs?

<p>Cretaceous Period (D)</p> Signup and view all the answers

Based on radiometric dating, what is the estimated age of the Earth?

<p>4.6 billion years old (D)</p> Signup and view all the answers

In the context of the geologic time scale, what does 'Ga' stand for?

<p>Billions of years (B)</p> Signup and view all the answers

During which interval were prokaryotic life the only form of life present?

<p>Precambrian (A)</p> Signup and view all the answers

Why is the Hadean Eon the least understood compared to other eons?

<p>No rocks from this time period have been preserved on Earth. (C)</p> Signup and view all the answers

During which eon did the first photosynthetic organisms appear, leading to a significant change in Earth's atmosphere?

<p>Archean Eon (B)</p> Signup and view all the answers

What is the primary distinction between organisms that appeared in the Archean Eon versus those in the Proterozoic Eon?

<p>Archean organisms were prokaryotes, while Proterozoic organisms included the first eukaryotes. (A)</p> Signup and view all the answers

Which evolutionary milestone occurred during the Proterozoic Eon, marking a significant step towards greater biological complexity?

<p>Emergence of the first multicellular organisms (D)</p> Signup and view all the answers

What is the significance of the Cambrian Period in the context of the Paleozoic Era?

<p>It featured a rapid diversification of marine invertebrates, known as the Cambrian explosion. (D)</p> Signup and view all the answers

What evolutionary advantage did vascular plants develop during the Silurian period, allowing them to thrive on land?

<p>Specialized tissues for water and nutrient transport (A)</p> Signup and view all the answers

During which period did lobe-finned fishes evolve, representing a crucial step towards the evolution of terrestrial vertebrates?

<p>Devonian Period (D)</p> Signup and view all the answers

What adaptation allowed seed plants to become the most common type of land plant during the Devonian period?

<p>Ability to reproduce independently of water (C)</p> Signup and view all the answers

Flashcards

Amphibians

The first animals evolved to colonize land, needing water to reproduce.

Carboniferous Period

A time when widespread forests left carbon deposits that became coal.

Reptiles

First animals that could reproduce on dry land, evolving from amphibians.

Pangea

A supercontinent formed by colliding land masses during the Permian Period.

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Permian Extinction

The largest mass extinction event, marking the end of the Permian Period.

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Mesozoic Era

An era known as the 'Age of Reptiles', starting over 280 million years ago.

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Jurassic Period

The period known as the 'Golden Age of Dinosaurs' with the first birds and flowering plants.

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Cenozoic Era

The era known as 'recent life', starting 65.5 million years ago, evolving into today's flora and fauna.

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Hadean Eon

Earliest eon from 4.6 to 4 billion years ago, least understood due to lack of preserved rocks.

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Archean Eon

Lasted from 4 billion to 2.5 billion years ago; Earth's crust solidified and first simple life forms appeared.

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Prokaryotes

First life forms; single-celled organisms that lacked a nucleus and were anaerobic.

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Cyanobacteria

The first photosynthetic organisms on Earth, also known as blue-green algae.

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Proterozoic Eon

Lasted from 2.5 billion to 541 million years ago; atmospheric and oceanic oxygen levels increased; multicellular life emerged.

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Paleozoic Era

Age of Ancient Life; spans from the end of Precambrian to the beginning of Mesozoic.

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Cambrian Period

541 to 485.4 million years ago; marked by the Cambrian explosion of new organisms.

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Devonian Period

419.2 to 358.9 million years ago; seed plants evolved, and lobe-finned fish emerged.

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Geologic Time Scale (GTS)

A time scale dividing Earth's history into intervals by major events or changes.

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Eons

The largest intervals of geologic time, lasting hundreds of millions of years.

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Eras

Divisions of time that span periods of ten to hundreds of millions of years.

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Periods

Subdivisions of eras, covering no more than 100 million years each.

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Epochs

The smallest division in the Geologic Time Scale.

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Precambrian

The longest geologic time, covering 90% of Earth's history, from 4.6 billion to 542 million years ago.

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Prokaryotic Life

Simple, single-celled organisms that existed during the Precambrian without major events.

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Study Notes

Geologic Time Scale

  • The Geologic Time Scale (GTS) is a time scale that divides Earth's geologic history into intervals of time, defined by major events or changes.
  • It is a tabular representation of earth's history.
  • A record of life forms and geologic events in Earth's history.
  • The age of the Earth is 4.6 billion years old (using Radiometric dating).

Major Divisions of Geologic Time Scale

  • Eons: The largest intervals; lasting hundreds of millions of years.
  • Eras: Divisions spanning ten to hundreds of millions of years. Subdivided by eons.
  • Periods: Subdivided by eras, typically lasting no more than 100 million years.
  • Epochs: The smallest division on the geologic time scale.

Time Intervals (Longest to Shortest)

  • Eons are the longest (hundreds of millions of years).
  • Eras span time periods of ten to hundreds of millions of years.
  • Periods are subdivided by eras and last no more than 100 million years.
  • Epochs are the smallest divisions on the scale.

Time Units

  • Ka = Kilo annum (thousands of years)
  • Ma = Mega annum (millions of years)
  • Ga = Giga annum (billions of years)

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