Objective: Learn the Causes and Effects of Mass Extinctions

1. What does “extinction” mean?

2. What is the rate of extinct species in the planet?

3. What is the average existence of a species before dying out?

4. What causes extinction?

5. How are evolution and extinction in balance?

Video Clip: http://www.pbs.org/wgbh/evolution/extinction/index.html

1. Point out the extinction events on the graph using an arrow2. Label the extinctions you pointed out on the graph

CretaciousTertiary

TriassicJurasic

PermianTriassic

Late Devonian

OrdovicianSilurian

Objective: Learn the Causes and Effects of Mass Extinctions

3. List the mass extinction events from the earliest to the latest

4. List the mass extinction events from the most destructive to the leastOrdovician Silurian, Late Devonian, Permian Triassic, Triassic Jurasic, Cretacious Tertiary

Permian Triassic, Ordovician Silurian, Cretacious Tertiary, Late Devonian, Triassic Jurasic

Objective: Learn the Causes and Effects of Mass Extinctions

ExtinctionMore than 99 percent of all species that have ever lived are now extinct. Usually, extinctions happen for the reasons that Darwin proposed. Species compete for resources, and environments change. Some species adapt and survive. Others gradually become extinct in ways that are often caused by natural selection.

Several times in Earth's history, however, mass extinctions wiped out entire ecosystems. Food webs collapsed, and this disrupted energy flow through the biosphere. During these events, some biologists propose, many species became extinct because their environment was collapsing around them, rather than because they were unable to compete. Under these environmental pressures, extinction is not necessarily related to ordinary natural selection.

Until recently, most researchers looked for a single, major cause for each mass extinction. For example, one hypothesis suggests that at the end of the Cretaceous Period, the impact of a huge asteroid wiped out the dinosaurs and many other organisms. Scientific evidence confirms that an asteroid did strike Earth at that time. The impact threw huge amounts of dust and water vapor into the atmosphere and probably caused global climate change. It is reasonable to assume that this kind of event played a role in the end of the dinosaurs.

Many paleontologists, however, think that most mass extinctions were caused by several factors. During several mass extinctions, many large volcanoes were erupting, continents were moving, and sea levels were changing. Researchers have not yet determined the precise causes of mass extinctions.

What effects have mass extinctions had on the history of life? Each disappearance of so many species left habitats open and provided ecological opportunities for those organisms that survived. The result was often a burst of evolution that produced many new species. The extinction of the dinosaurs, for example, cleared the way for the evolution of modern mammals and birds.

Objective: Learn the Causes and Effects of Mass Extinctions

Causes of Extinction Effects

1. What is the rate of extinct species in the planet?

2. Complete the following chart about causes of extinction and effects

3. What was the result of the extinction of the dinosaurs?

4. What does “extinction” mean?

More than 99 percent of all species that have ever lived are now extinct.

• Increase competition for resourcesEnvironmental changes:

• Impact of huge asteroids• Global climate change• Large volcanoes eruption• Continents moving• Sea level changes

• Mass extinctions• Food webs collapsed• Disruption of energy flow in ecosystem

• New opportunities for new or existing species. Example: birds & modern mammals

It gave opportunities for the evolution and expansion of modern mammals and birds.

It means species that dies out and no longer has any living members.

Objective: Learn the Causes and Effects of Mass Extinctions

5. Explain the effects of mass extinctions on the history of life.• Food webs collapsed• Disruption of energy flow in ecosystem• New opportunities for new or existing species.

Objective: Learn the Causes and Effects of Mass Extinctions

Species B and C share a closer ancestor (F) than species A and C.