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! 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: The main source of iridium is from outer space in the form of space dust which is constantly showering our planet 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 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 Intense heat started fires Loss of habitat Loss of food/ water Debris, gases, dust into atomosphere Darkened sky- cooler climate, Fires releasing carbon dioxide- greenhouse 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….. 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…