PYTR Class

Learning Objectives

1. Describe how Earth’s 4.5-billion-year history and long-term geological processes have contributed to the evolution of life.
2. Explain how Earth’s history is divided into geological epochs based on evidence from the fossil record.
3. Describe how mass extinctions are typically followed by rapid speciation due to the opening of ecological niches.
4. Define the Anthropocene as a proposed geological epoch marked by significant human-driven environmental change and species extinction.
5. Explain how current human activities are creating global changes that will be evident in the geological record.

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Part 1: Eons and Epochs

The geological timescale is divided into eons, which are further classified into eras periods and epochs

Key terminologies

• Eon = A unit of time
• Era = A unit of time. Shorter than eon but longer than a period
• Period = A unit of time. Shorter than era but longer than epoch
• Epoch = A unit of time. Shorter than period but longer than an age

• Evolution of life on Earth started 4.5 billion years ago.
• Previous organisms died and become  part of the Earth’s crust layers. 
• The inner layers of the earth crust contain older fossils

Part 2: Mass Extinction Events

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The Ordovician–Silurian extinction

439 mil years ago

• Glaciers formed – dropping sea level
• Killed 86% species

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The Late Devonian extinction

364 mil years ago

• Global cooling
• Diversification of plants dropping the level of CO₂
• Killed 75% of all species

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The Permian–Triassic extinction

251 mil years ago

• Largest extinction event
• May be due to an asteroid (but not evidence yet) and may also be due to the tectonic movement (Pangaea formation)
• Others believe the cause was volcanic activity, as with the End Triassic extinction, from the Siberian Traps
• Algae and plants died causing drop in O₂ level

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The End Triassic extinction

199 – 214 mil years ago

• Widespread of volcanic eruptions
• Huge emission of CO₂ and CH₄
• CO₂ acidified the ocean
• 80% of species went extinct

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The Cretaceous–Tertiary extinction

65 mil years ago

• Caused by the impact of a several-mile-wide asteroid that created a huge crater, which is now hidden beneath the Gulf of Mexico. 
• Reduced sunlight
• Drop in temperature
• Flood-like volcanic eruptions
• Climate change
• Tectonic rearrangement
• 76% of species went extinct

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Sixth Mass Extinction?

• Phase 1: began when the  first modern humans began to disperse to different parts of the world about 100,000 years ago
• Phase 2: began about 10,000 years ago when humans turned to agriculture.

• Approximately only 1% of the species from the previous era still exist today. 
• Although the mass extinction events killed many species, each event gave new direction for biodiversity
• The large-scale loss of species led to new opportunities for surviving populations, with many groups undergoing adaptive radiation

Part 3: The Anthropocene

Holocene and Anthropocene

• Holocene – quaternary period – which existed for about 2 million years, was distinguished by regular shifts into and out of glacial and inter-glacial phases
• Scientists believe that we have entered a new epoch called the Anthropocene
  • Great Acceleration = dramatic, continuous, approximately simultaneous and rapid increase of factors across a large range of measures of human activity
  • first recorded in the mid-20th century and continue to this day

Evidence of Anthropocene

• signals from chemical pollution are currently accumulating in geological strata, with the potential to be preserved into the far future
• mixing of native and non-native species, which will be represented in the fossil record 
• deposits from nuclear testing
• modification of terrestrial and marine sedimentary systems
• minerals created solely or primarily from human activity

Types of Extinction

1. Local extinction (extirpation) species no longer found in an area where it was once found
2. Ecological extinction so few members of a species are left that it can no longer play its ecological role in the ecosystem
3. Biological extinction species is no longer found anywhere on the earth

Notes and Exercise