The K-T Extinction event was triggered by a large scale asteroid impact that decimated the planet.

Approximately sixty-five million years ago, at the end of the Cretaceous period, an event occurred which decimated 90% of the species on the planet at the time. The main causes proposed for this event are the impact theory and the Alvarez theory, which are very similar. Most of the evidence used for these theories comes from the K-T Boundary. This Boundary is a line in the sedimentary rock in the Earth.

Various Viewpoints

In my research, I have discovered two different viewpoints about what could have happened to the dinosaurs sixty five million years ago.

Impact Theory

The impact theory suggests that the dinosaurs were decimated in an extraterrestrial impact. This impact has been calculated at being over 6 miles across, weighed 2 trillion tonnes, and hit the Earth with the force of 100 million megatons. Whilst travelling through the atmosphere the asteroid was transformed into a fireball and superheated the atmosphere. The impact of the asteroid caused a chain reaction of events:

• The impact of the asteroid sent boulders the size of buildings into the air which fell back to Earth as deadly projectiles at 100,000 miles per hour.
• Heat from the asteroid would have been hot enough to boil water in both plants and dinosaurs.
• The force of the impact sent shock waves into the planet and created an earthquake that would have measured 11.1 on the Richter scale.
• The blast pulse wave of the impact was faster than the speed of sound and could have ripped the skin off flesh.
• The force of the impact also sent 70 billion tonnes of pulverized stone and earth into the upper atmosphere creating an Ejector Cloud.
•  Friction within the cloud heated it to 15,000 degrees and baked the Earth
• A combination of an electrical storm and the heat of the Ejector Cloud ignited fires across the planet. The fires are thought to have reached 1,800 degrees and created winds. These fires moved at 9 miles per hour.
• The strain of the impact caused sedimentary rock to collapse under the sea which created a mega tsunami. The tsunami is estimated to have been 300 feet tall and hit 13,000 miles of coast line across the planet.
• Seismic shock waves that went through the planets core forced molten rock upwards resulting in massive volcanic eruptions. These eruptions added debris to the Ejector Cloud.
• The Ejector Cloud stopped heat and light from the sun reaching the Earth’s surface. This resulted in a nuclear winter and stopped photosynthesis throughout the planet.
• Hydrogen sulphide from the volcano rose into the water and the gases were released into the air. This particular gas paralyses the lungs and causes suffocation. 

Alvarez Hypothesis

Walter Alvarez, a geologist, and his son, Luis, a physicist, first detailed the impact theory associated with the Chicxulub crater in 1978. The Alvarez team analysed sediment found in the K-T layer of rock. The samples of sediment found in the layer showed an irregularly high concentration of iridium, an elemental substance that is rare on Earth, but found in large quantities in asteroids. Other samples from around the world were analysed and were found to have the same element. Using this data, they believed that an asteroid with a diameter of 6 miles (10 kilometres) would be needed to spread the iridium that far around the world. These discoveries lead the Alvarez team to conclude that an asteroid had impacted with the Earth about 65 million years ago and resulted in the mass extinction of the dinosaurs.

Keller Hypothesis

Gerta Keller, a palaeontologist, argues that the K-T Boundary was created 300,000 years before the extinction event occurred. The evidence found that supports this theory, in incredibly simple terms, is that, after examining samples of the rock above and beneath the K-T Boundary, Keller found that certain species of marine zooplankton on both sides of the boundary. This evidence led her to believe that the Chicxulub impact could not have been the cause for the extinction.

Conclusion

After extensive research into this topic, the most likely cause for the mass extinction of the dinosaurs sixty-five million years ago is the asteroid impact and it’s after affects. The impact itself was devastating to both the planet and the dinosaurs, however, it is the after affects that really killed off the dinosaurs. Although the evidence from Gerta Keller is compelling, it doesn’t seem to be entirely convincing. The Alvarez Hypothesis is supported by more evidence, and the evidence makes more sense than what Keller has offered.  

Reflection

Researching this topic was a lot harder than it was initially thought. Searching online library catalogues was hard, but actually going to the library and physically searching the shelves was much easier. Trying to find useful websites was the hardest part of the whole process. Most of the identified search terms weren’t useful in searching for websites or for books and DVDs. In the end, finding the online websites was a matter of searching for the words ‘dinosaur extinction’ and searching through the results.

Annotated Bibliography

Coffey, J. (2009) ‘Universe Today’. Asteroid Extinction Theory. [Online]. Available at <http://www.universetoday.com/36706/asteroid-extinction-theory/ > accessed 13 November 2011.

The article by Jerry Coffey is a useful source for beginners trying to understand the impact theory of dinosaur extinction. The article is very easy to read and understand. Although short, the article manages to go into a fair amount of detail about the event and the slight variations involved with the impact event theory.

Dixon, D. and Malam, J. (2006) Dinosaur. DK Publishing, New York.

Dinosaur was published by Dorling Kindersley, in conjunction with Google. The book gives an excellent overview of everything to do with dinosaurs, from what a dinosaur is to how and why a dinosaur is displayed in a museum. The section in the book on the mass extinction of the dinosaurs is brief yet succinct. The book is easy to understand as it is aimed at primary school children, yet the information is precise.

Last day of the dinosaurs. (2011) [Videorecording] Discovery Channel, Australia.

This Discovery Channel program interweaves a personal story into the subject of the extinction. The program gives the information about the asteroid impact within the story of several dinosaur species, and some individual ones. The program is a reliable source of information and is a useful source for anyone studying the dinosaur extinction event.

Palmer, D. (1999) The atlas of the prehistoric world. Marshall Publishing, London.

The Atlas to the Prehistoric World, published in association with the Discovery Channel, mainly focuses on the changing face of the planet over the millennia and how life has evolved. The book does contain some very insightful sections on the K-T Boundary and the physical impact from the asteroid. The text in the book is coupled with images that correlate well with the information and provide visual aids. The book is easy to understand for people in high school or higher.

Svarney, T. E.  and Svarney, P. B. (2003) The handy dinosaur answer book.  Visible Ink Press, London.

The Handy Dinosaur Answer Book is an excellent resource for studying dinosaurs. The book is split into several sections, covering topics including dinosaur anatomy, dinosaur behaviour and what happened to the dinosaurs. Each of these separate sections give their information in terms of the answer to a question that has been posed. The information is set out well and the information is easy to understand.

The Chicxulub Debate. (2004) [Internet]. Available at <http://geoweb.princeton.edu/people/faculty/keller/chicxpage1.html> accessed 24 October 2011.

The Chicxulub Debate is a paper written in 2004 by Gerta Keller, a leading palaeontologist based in America. The paper goes into great detail about her discoveries in relation to the Chicxulub crater and her theories about what happened when it occurred. The paper is very difficult to read and seems to repeat itself more than is necessary.

Proposed Research Strategy

Bibliographic Sources:

• Encyclopedias (aimed at mid-level readers)
• Online periodical databases
• Britannica Online
• Books on the subject

I've selected to search these types of resources for two reasons:

1. They should have very specific information on the subject

2. The resources will be easier to read and understand, i.e. little to no scientific jargon. 

Specific Searching Tools
The specific tools for searching will range from library catalogues (TAFE, public and possibly universities) to Trove. Online periodical databases will be found through the State Library of NSW eResources section.

Search Terms:

Official LCSH: Dinosaurs -- Extinction

Thesaurus terms: Extinction - decimation, extermination.

NB: No other terms for dinosaur unless I search for a specific species.

Other terms used in searching: K-T extinction event, Dinosaur extinction, Dinosaurs extinction

Types of Searches
In researching this topic, I plan to use the above terms, along with any others I find, in search engines, online periodicals databases and library catalogues.

I will need to limit the search to the specific K-T extinction event instead of the numerous other occasions where certain species of dinosaurs were made extinct. This means that I will need to include the term "K-T extinction event", or some variation thereof in searching. I'm not quite sure how to go about limiting the search using other names associated with the other events, but at this stage I don't think that anything to do with those events will come up in the searches as they aren't as well known. Despite this I will ensure that the term "Ice Age" is excluded.

Research Question

Original Question:
The causes of the K-T Extinction event were triggered by a series of asteroid impacts in six locations across the globe.

New Question:
The K-T Extinction event was triggered by a series of large scale asteroid impacts in six locations across the globe.

Second New Question:
The K-T Extinction event was triggered by a large scale asteroid impact that decimated the planet.

Concept Map

NB: In  the bubble that says "Survival of birds & small" the missing word is "mammals". For whatever reason the word was cut out when I converted the map to an image.

Possible Explanations for the K-T Extinction

Asteroid Theory


The asteroid theory is based on the finding of Luis Alvarez, a physicist, and his son, Walter Alvarez, a geologist. In 1980, they discovered that sedimentary layers found at K-T Boundary contain a concentration of iridium many times greater than normal. Iridium is extremely rare in the earth's crust because it is a "siderophile element" ("iron-loving"), meaning that most of it travelled with the iron as it sunk into the earth's core. As the element remains in high quantities in most asteroids and comets, the Alvarez team suggested that an asteroid had struck the earth at the time of the K-T Boundary. This was the first evidence uncovered that supported the asteroid theory. 


An impact of this magnitude would have caused a massive amount of dust and debris creating a dust cloud, which would have blocked the sun for 6 to 12 months and inhibited photosynthesis. The impact also would have sent sulfuric acid aerosols into the stratosphere, which would have reduced the sunlight reaching the Earth's surface by 10-20%. It would have taken up to ten years for those aerosols to dissipate.


This hypothesis was disputed and even disregarded by many scientists and paleontologists for many years. However, today most scientists have accepted the theory and have even established where the asteroid may have impacted: Chicxulub, Mexico. The crater is not visible on land, but powerful photographs taken in space clearly show the crater. 





However, in 2004 scientists who were doing research on the crater said that a core drilled out of the middle of the crater dated back to more than 300,000 years before the K-T Boundary, and therefore could not have caused the mass extinction.


There are other craters around the world which scientists believe may have contributed to the extinction. This theory is known as a multiple-impact event. These craters are:

• Boltysh crater, Ukraine
• Shiva crater, Indian Ocean
• Silverpit crater, North Sea
• Eagle Butte crater, Canada
• Vista Alegre crater, Brazil

Overview 2: Terms associated with the subject

K-T Extinction -- Cretaceous and Tertiary periods when the extinction occurred

K-T Boundary -- a "geological signature", usually a thin band. The boundary marks the end of the Mesozoic era and the beginning of the Cenozoic era, and is associated with the extinction event.



Mesozoic era -- 250-65 million years ago, known as the Age of Dinosaurs because of its association with non-avian (bird) dinosaurs. Lasted for roughly 180 million years. Can be separated into the Triassic, Jurassic, and Cretaceous periods.



Triassic -- 250 to 200 million years ago. During this period, both marine and continental life show an adaptive radiation. The first flying vertebrates, the pterosaurs, evolved in this period.


Coelophysis, one of the first dinosaurs, appeared in this period

Pterosaurs -- flying reptiles, e.g. pterodactylus.






Adaptive Radiation -- the evolution of an animal or plant group into a wide variety of types adapted to specialized modes of life.



Jurassic -- about 200 to 145 million years ago. The middle of the Mesozoic era, also knows as the Age of Reptiles.


Stegosaurus, this period saw the emergence of large herbivore dinosaurs

Cretaceous period -- 145 to 65 million years ago. This period lasted for 80 million years. This period ended with the extinction of many species, including non-avian dinosaurs, pterosaurs and large marine reptiles.


The Tyrannosaurs lived during this period


Cenozoic era -- the current era beginning approximately 65 million years ago. It is marked by the extinction event that saw the demise of the last non-avian dinosaurs and the end of the Mesozoic era. The Cenozoic era is ongoing. Divided into three periods: the Paleogene, Neogene, and Quaternary. Also known as the Age of Mammals.


The Mammoth, along with other animals such as the saber-toothed cat, emerged in this period



Paleogene -- the first part of the Cenozoic era, beginning 65.5 million years ago and ending 23.03 million years ago. Lasting 42 million years, this period is notable for being the time when mammals evolved following the extinction event. Some of these mammals evolved into larger forms that dominated the land, while others became capable of living in marine, specialized terrestrial and even airborne environments. Birds also changed into roughly modern forms.


Among other amnials, this period saw the beginning of the earliest whales.


Neogene -- second part of the Cenozoic era, beginning 23.03 million years ago and ending 2.588 million years ago.


Three-toed horses and other strange animals lived in this time

Quaternary -- the most recent of the Cenozoic era, beginning 2.588 million years ago to the present day


Arctodus 


Tertiary period -- 65 to 2.6 million years ago. This period began with the extinction and spanned to the beginning of the most recent Ice Age.

Overview 1: General

The extinction of the dinosaurs is believed to have occurred between 65 and 66 million years ago. This period is known as the K-T extinction. The K is the geological symbol for the Cretaceous period, while the T stands for the Tertiary period.

Scientists have developed many different theories to explain what happened to the dinosaurs. However, the two major theories are:

• Gradual climate change, and
• The asteroid theory
  

The Climate change theory states that: "towards the end of the Cretaceous period, the shallow seas dried up and the climate became more varied everywhere around the globe. Winters became too cold and summers too hot for dinosaurs to survive. Dinosaurs were too large to hibernate in dens, and they had no fur for protection against the cold. They also probably had difficulty cooling off in hot weather." -- World Book, 2007, Volume 5.

The Asteroid theory states that: "a large asteroid hit Earth at the end of the Cretaceous. This asteroid impact would have thrown billions of tons of dust and debris into the atmosphere. Heat from the impact may have cause huge fires worldwide. Together, the clouds of smoke and debris would have blocked sunlight from reaching the surface of the Earth for many months. Although the seeds and roots of plants had a good chance of surviving this light less period, the plants themselves stopped growing and died. Because such a catastrophe would have been severe and widespread, plant-eating dinosaurs would have starved to death. As the plant-eaters died, so did the meat eating dinosaurs that fed on them. In addition, the darkened skies caused land temperatures to drop below freezing for 6 to 12 months in many parts of the world." -- World Book, 2007, Volume 5.

Most scientists agree that no single theory completely explains why the dinosaurs suffered near complete extinction. They argue that a combination of causes attributed to the disappearance of dinosaurs.

However, scientists agree that not all dinosaurs became extinct. They regard birds as living dinosaurs that survived the extinction. We can also see the link between dinosaurs and certain modern animals, such as crocodiles and lizards.