Transcript File

Extinction Theories
There have been many mass extinctions throughout the
history of the Earth, but the most famous is the extinction
that saw the end of the dinosaurs reign, 65 million years
ago.
The two main theories to explain the extinction
of the dinosaurs and 70% of all species on
Earth are:
1. Asteroid Theory
2. Volcano Theory
Impact Theory
Throughout our history there have been many large and small
impacts. The results can have wide variations as well.
Evidence:
The Tunguska Fireball
On June 30, 1908 an area near the Tunguska River in Siberia
was the site of a remarkable explosion. The explosion
caused a shock wave that flattened most forests covering an
area of more than 1000 square kilometres. The explosion
killed herds of reindeer, sheep and other animals. It broke
windows and knocked people to the ground 60 km away!
Scientists believe that the explosion was caused by an object
with an approximate weight of 100,000 tonnes.
Evidence:The Barringer Meteor Crater
located in northern Arizona, this bowl shaped
depression is 180 m deep and 1.2 km in diameter!
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• In 1905 Daniel Barringer theorized that the crater
was meteroric in origin
• Thought to be formed between 25 000 and 50 000
yrs ago by a meteorite 30-100 m in diameter and
weighing 60 000 tonnes.
• The energy released upon impact is equivalent to
3.5 million tonnes of dynamite!
Canadian
Evidence!
Close to Home!
• Near Ottawa
Near Sudbury
Impact Maps
North American Impact Sites
What is Iridium?
Iridium is a rare element only found in
abundance in two locations:
1. The main source of iridium is from
outer space in the form of space
dust which is constantly showering
our planet
2. The second source is the Earth’s
core when there are eruptions of
certain types of volcanoes.
The increased presence of iridium in
the thin layer between Cretaceous
and Tertiary Rocks supports both
the asteroid and volcano theories.
A Closer Look at the Asteroid/Impact
Theory
Supporting Evidence
• Iridium found in many sediments of the
Cretaceous. This element is a common
component of meteors and asteroids
• Shocked quartz samples were found.
These crystals are only physically altered
under extreme temperature and pressure.
• A crater was found along the coast of Yucatan
in Mexico called the Chixculub.
• The ring structure is 180 km in diameter.
• Using Ar 40/ Ar 39 dating method, it has been
dated to be 65 million years old
• The impacting body was about 10 km in
diameter.
• The estimated velocity at which it struck the earth
was 100 000 km/hr!
* The crater is buried beneath several hundred
metres of sediment.
• Evidence of acid rain was found in a number
of rock samples.
• Carbon soot, indicative of wild fires was
found.
• Temperature data shows a temperature drop
and later a temperature rise.
Outstanding Problems with the
Impact Theory
• Other impacts: there were other craters
during the Mesozoic era that did not cause
associated extinctions.
• Amphibians, who are vulnerable to the
slightest environmental change, survived
the event.
• Iridium has been found in the greatest
abundance 10 000 km away from
Chicxulub. Iridium found in Mexico does
not bear the same date.
More problems…
• Some evidence indicates that shocked
quartz could be volcanic or tectonic, not
originating from space.
• Typical meteoric metals are not found at
all impact sites.
• The greatest mass extinctions should be
nearest the impact site. The greatest
dinosaur graveyard is in the Gobi Desert
on the other side of the Earth!
The Volcanic Theory
• The idea of a volcanic event blasting vast
quantities of gases into the atmosphere
and lava flooding the land is debated
amongst scientists as well!
• India had vast lava flows in an area
known as the Deccan Traps. The lava
covered an area as big as France!
• Other areas including Canada, show
evidence of massive lava flows.
Evidence continued..
• The eruptions could explain the drastic
weather changes including a darkened
sky, climatic cooling and acid rain.
• Both iridium and shocked quartz can be
caused by volcanic eruptions.
• Hot lava could have caused widespread
fires and consequently, carbon and soot.
• Eruptions would last longer than an
impact, which may explain iridium dates.
Problems with the Volcanic Theory!
• How could fires start in an area of India
surrounded by seas?
• No iridium has been found in the Deccan
Traps.
• Could volcanic eruptions send iridium
globally?
• Three other massive flood basalts on
record are not connected with any mass
extinctions.
Interactions among the four
spheres
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Intense heat started fires
Loss of habitat
Loss of food/ water
Debris, gases, dust into atomosphere
Darkened sky- cooler climate,
Fires releasing carbon dioxidegreenhouse effect.
• Blast would have triggered tidal waves
Interactions continued..
• Winds from blast would carry debris and gases
great distances.
• Many organisms rely on sun for warmth
• Ferns moved into area where fires once burned.
• Oxygen in seawater would decrease as currents
bring to the surface water low in oxygen.
• Death of plankton disrupts marine food chain
• Acidity of sea from acid rain would kill marine
life
Other Extinction Possibilities!
• Disease
• Climate change
• Radiation
How about this?
• The hyper-sound theory claims that the sound
of the impact damaged many animals inner ear
mechanisms.
• Damage to these structures will result in loss of
balance and thus difficulty standing, walking,
running, swimming or mating, especially for
large animals and reptiles.( small birds, lizards,
snakes, crocodiles, turtles, frogs, birds and
mammals under 25 kg survived the K-T impact)
Hyper-sound continued..
• Sound travels better through water, so
this may also explain the alarming 93% of
ocean dwelling reptiles that became
extinct.
• Increased water pressure from the impact
may have damaged inner ear mechanisms
as well.
Other theories…!
What Goes Around Comes
Around…..
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Frequency of Impacts:
pea-sized meteoroids- 10 per hour
walnut sized
- 1 per hour
grapefruit sized
- 1 every 10 hours
basketball sized
- 1 per month
50 m rock that would destroy an area the size of
New Jersey
- 1 per 100 years
1 km asteroid
- 1 per 100 000 yrs
2 km asteroid
- 1 per 500 000 yrs
And the research continues…