Today’s Topic Evolution: Extinction

Learning Goal:

SWBAT explain why creatures go extinct from

Earth, and why some recently-extinct creatures

have gone extinct.

Please take out your fill-in notes again,

and we will continue learning about

extinct creatures .

Homework

Complete the Simulating Adaptations Lab

(One Day Late)

Complete cattle, cows, and dogs articles.

(Three Days Late)

Complete the Conditions of Natural

Selection homework and History of

Evolution Research Assignment.

(Four Days Late)

Upcoming Test

Our next test will take place on

Wednesday, 4/15.

It will cover all of Evolution:

Biological Evolution

Natural Selection

Artificial Selection

Adaptations

Extinction

Succession

Today’s Fill-In Notes

We’re next going to work through the five

mass-extinction events that took place on

Earth.

After that, we are going to watch the

beginning of an episode of Cosmos

regarding one of the extinction events.

The Five Mass-Extinction Events

Throughout Earth’s history there have

been many extinction events.

However, there has been five mass-

extinction events that occurred in Earth’s

history.

In a mass-extinction event, over 50% of

all plant and animal life go extinct.

The Five Mass-Extinction Events

The Five Mass-Extinction Events that

occurred are:

a. The Ordovician-Silurian (450 – 440

Mya)

b. The Late Devonian (375 – 360 Mya)

c. Permian-Triassic (252 Mya) (Cosmos)

d. Triassic-Jurassic (201.3 Mya)

e. Cretaceous-Plaeogene (66 Mya)

The Ordovician-Silurian

The Ordovician-Silurian mass-extinction

occurred approximately 450 – 440 Mya at

the end of the Ordovician Period.

Typically large scale events, such as

mass-extinctions, mark the end of a

geologic time period.

During this time, 70% of all species on

Earth were killed.

The Ordovician-Silurian During this period of time, all life existed

in the oceans.

The Ordovician-Silurian However, two events occurred, an

estimated four million years apart, that

set off this mass-extinction event.

The Ordovician-Silurian First was the movement of the super-

continent of Gondwana.

Gondwana, through tectonic plate

movement, shifted towards the south.

This in turn led to

global cooling.

The Ordovician-Silurian As a result of this global cooling, glaciers

began to form all over the planet.

This caused a drop in sea levels, which

further killed off many creatures.

The Late Devonian

The Late Devonian mass-extinction

occurred approximately 375 – 360 Mya at

the transition from the Devonian Period

to the Carboniferous Period.

This extinction event caused 70% of all

creatures on Earth to perish.

The Late Devonian It is unclear what caused the mass-

extinction, but evidence suggests that it

was not one singular event that triggered

the extinction.

It is thought that several small events

occurred over the span of 20 million

years.

The Late Devonian This extinction event only appeared to

affected marine life.

Some theories as to what caused the

extinction event are changed to ocean

levels, or depletion of oxygen in oceans.

This would have been caused by volcanic

activity in the ocean.

The Triassic-Jurassic

The Triassic-Jurassic mass-extinction

occurred approximately 201.3 Mya at the

end of the Triassic Period.

This extinction event caused 70% - 75%

of all creatures on Earth to go extinct.

The Triassic-Jurassic

Land and air-dwelling dinosaurs survived

perfectly well through this extinction

event.

The Triassic-Jurassic

However, non-dinosaur aquatic creatures

in the oceans continued to dominate the

oceans.

The Triassic-Jurassic There are many theories as to what

caused the extinction event:

Gradual climate change

Sea-level fluctuations

Ocean acidification

The Triassic-Jurassic One theory suggests the possibility of an

asteroid impact.

However, none of these hypotheses have

any significant evidence to support them.

The Cretaceous-Paleogene

The Cretaceous-Paleogene mass-

extinction occurred approximately

66 Mya at the end of the Cretaceous

Period.

This extinction event caused 75% of all

creatures on Earth to go extinct.

The Cretaceous-Paleogene

This extinction event killed all non-avian

(non-flying) dinosaurs.

The Cretaceous-Paleogene This extinction event was believed to

have been caused by a massive

comet/asteroid impact.

The Cretaceous-Paleogene The impact had dire effects on the entire

globe’s environment.

The Cretaceous-Paleogene The dark line in the rock marks this event

The Cretaceous-Paleogene Sampling shows higher concentrations

(30x higher than naturally found on

Earth) of iridium in this region, which is

prevalent in meteors and comets.

It also corresponds

to ash and carbon,

as the impact

triggered many fires

(high O2 levels)

The Cretaceous-Paleogene The impact caused an impact-winter,

which is caused by an ejection of dust

and dirt into Earth’s atmosphere.

This dust and dirt

blocks sunlight from

entering, which

prevents

photosynthesis from

occurring in plants

and plankton.

The Permian-Triassic To learn about the Permian-Triassic

extinction event, we turn to our friend

Neil deGrasse Tyson.