What Killed the Dinosaurs?

• You are going to be given a set of cards with the following theories on them.

Your task is to arrange the theories in order of the most likely cause for the extinction of dinosaurs to the least likely reason.

Asteroid Strike.

Scientists believe an Asteroid struck the Earth and killed the dinosaurs.

Evidence:

Palaeontologists Luis and Walter Alvarez discovered an unusual layer of clay far below the Earth’s surface in Italy. The layer contained Iridium (a rare element) and traces of soot. Iridium is usually found in outer space and makes up ‘cosmic dust’. Alvarez senior said this proved an asteroid had struck as the soot was a sign of the huge global fires that would have resulted.

The size of the asteroid would have produced a lot of energy on impact which would have killed dinosaurs instantly, any dinosaurs that had survived the impact would have died from starvation shortly after due to the loss of vegetation caused by huge global fires. The fires would have posed a problem for dinosaurs as they would have destroyed their habitats and their food sources.

The Palaeocene Theory.

This theory supports the idea of a gradual decline in dinosaur numbers rather than a mass extinction.

Evidence: The San Juan Basin in the west of America offers evidence for the idea that not all dinosaurs died at the same time. During a dig in 2001 palaeontologists found skeletal remains of three species of dinosaur whose bones were believed to have shown that non-bird species had relocated to other areas of the world (possibly after a catastrophic event) and continued to live there for many years.

The bone fragments showed no signs of wear and tear, scratches, dents or other abrasions and were completely smooth which dismissed ideas that bones had been transported to the region by water.

Pollen was also found close to the bones, this pollen has already been dated to a later period than the life span of dinosaurs. This helps the argument that the dinosaurs died out gradually and were not all made extinct at the same time.

Climate Change.

Even the dinosaurs couldn’t escape the effects of climate change!!

Evidence: Scientists believe that the climate and atmosphere on Earth has constantly cycled and changed. Scientists believe thetemperature rose due to excess carbon dioxide in the atmosphere.

This concentration of CO2 would have killed dinosaur embryos, removed much needed oxygen from the seas so that sea living dinosaurs would have died too. The increase in temperature would have been caused by the growth of algae due to CO2 levels.

Dinosaur’s gender was decided on by the temperature during incubation and with the increase of temperature due to a change in climate, more female dinosaurs would have been born therefore gradually reducing the population sizes and decreasing the rate of reproduction between a species.

Disease.

A theory to suggest that several ways of viruses and new diseases appearing or being spread by the migration of species.

Evidence: Epidemics of new disease were enough to wipe out the dinosaur, a lot like mutations in

microbes today these were too powerful for the immune systems to handle. These diseases may have been the result of bacterial and viral evolution, due to migration of different species of animal who were carriers of a particular illness.

Scientists also believe that disease may have wiped out vegetation meaning whole food chains were affected, if plants and trees were no longer available to herbivores they would begin to starve and as a result so would carnivorous dinosaurs who fed on them.

With the immune systems unable to adapt quickly enough to combat these microbes, the dinosaurs would have been wiped out by something a lot smaller than itself.

Gravitational Change.

Dinosaurs were killed off by the consequences of Gravity changing on Earth.

Evidence: The size of gravity changed possibly due to a change In the orbit of Earth. The change in gravity is similar to the change in energy needed by electrons to move to another energy level. This change in gravity meant that dinosaurs were now to heavy to hunt, move and ultimately live. This change in gravity did not affect other life forms such as birds and reptiles because they had already undergone evolutionary changes. Birds are ‘designed’ to fly. The change in value for gravity meant that water became denser and heavier causing pressure changes in the seas. Sharks, fish and other life who were used to living in deeper areas of the seas were not affected by this change but it meant they could live in other locations too.

Continental Drift.The effects of the continent Pangaea splitting were disastrous for dinosaurs.

Evidence: Pangaea was once a supercontinent that has split to become the different ones we have today. The movement of the Earths plates caused tidal changes, it caused the currentsto change direction and led to rises in sea level in certain areas of the world.

These changes meant whole ecosystems changed and food became scarce. At this time there was flooding of many areas too, evidence for this floods include clams and fish fossils being found in mountains and in areas where you would not expect to find them. Scientists believe they have been found there as a result of being transported by water and then squashed in sedimentary rocks that have also been ‘washed up’.

Combined Events.

A general theory that suggests more than one factor caused the dinosaurs to be extinct.

Evidence: Fossil records and carbon dating of bones found all point to the fact that different species of dinosaur lived at

different times. This favours the idea that several different factors affected the lives and ultimately the demise of the dinosaurs.

The theory takes into account differences in climate that would force species to die out as they wouldn’t be able to adapt quick enough to survive in new conditions.

It also allows for factors such as new diseases, less food, volcanic eruptions and orbital changes to be taken into account.

The combined theory also gives weighting to the Palaeocene Theory.

Evolution.

Evolution not extinction!!

Evidence: Many scientists believe that many of the dinosaurs simplyevolved into many of the modern animals we have today rather than becoming extinct.

If you look at the characteristics and anatomy of many reptiles and lizards, you can see similarities between prehistoric creatures and these modern day animals.

Looking at the skeletons, bone fragments and fossils of flying dinosaurs and comparing these with the birds of today there are many structural similarities, the shape of the beak the joints of the wings etc.

These pieces of evidence back up the arguments that many species of dinosaur simply moved with the times and adapted!

Volcanic Activity.

Eruptions from volcanoes caused massive atmospheric changes.

Evidence: Volcanic eruptions caused molten rock to flow through giant cracks in the ground in an area called the Deccan Traps (this is now India). Land became covered inlayers of lava, destroying habitats and killing life.

Huge clouds of dust, sulphuric acid droplets, and noxious gases from the eruptions filled the air with poisonous fumes suffocating many life forms. As a result, the world's weather changed rapidly and the climate continued to be unpredictable for many years.

Fossils found in the area help to back up this theory as they show evidence of cooling and soil from the location shows traces of soot. The huge clouds also meant the sun was blocked this meant vegetation died which would have a huge impact on food chains at the time.

Out competed and

non-adapting.

Survival of the fittest!

Evidence:

One theory is that at the time of the dinosaurs there were many mammals and birds living alongside them. The theory suggests that due to atmospheric or climatic changes dinosaurs were out competed by animals that had furry coats to keep them warm, they also suggest that herbivores began to outcompete non-carnivorous dinosaurs for trees and plants.

Other ideas include dinosaurs being out competed for territory and eventually caused a decline in many of the species of dinosaur.