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An asteroid impact would be the cause of a mass extinction event.


The world today is going through the sixth largest mass extinction event in its history. As a part of GCSE Geography students will look at some of the causes of extinctions, but also what can be done to slow their rate - or even to bring some extinct species back to life.

A species is declared extinct when its last known member dies. Sometimes this happens in the wild, and it’s only after years of searching by scientists that the entire species is declared extinct. At other times it’s a rather public loss. The last known thylacine, or Tasmanian tiger, died in Hobart Zoo in 1936, just 59 days after the species was officially protected. There is limited evidence that some thylacines survived in the wild into the 1960s but little beyond that. However, the species wasn’t officially declared extinct until 1982.

A species might now be declared extinct, extinct in the wild, or just considered functionally extinct. Some species, such as the giant pangasius, are extremely threatened in the wild and possibly extinct. However, in captivity the giant pangasius is such a common species that it is often sold in supermarkets as food. It is also one of the main types of pet fish handed into rescues as they outgrow their aquariums. Functional extinction often occurs when the population of a species is too low to have enough genetic diversity for its numbers to have any hope of recovery.

Through time some species have gone extinct as the bulk of them have evolved into another distinct species. Several large scale extinctions (mass extinction events) have occurred when conditions have changed too rapidly for organisms to adapt and evolve to keep up with. The causes of these are thought to range from asteroid impacts to climate change. We are currently in the midst of another mass extinction as we lose species faster than at any other time since the Cretaceous-Tertiary Mass Extinction some 66 million years ago. That particular mass extinction is famed for the loss of the dinosaurs, but they were amongst thousands of other species that were also lost.

Try this quiz to see how well you know the causes of extinctions or what might bring about a mass extinction event.

The dodo was a large flightless bird that lived on Mauritius in the Indian Ocean. Shortly after the arrival of the Dutch to the island in 1638 the Dodo became extinct. Which of the following is not a reason they became extinct?
Dodos were hunted as a food source
Pig, rats and cats ate the dodos' eggs
Climate change affected the dodos' habitat
Dodos had no fear of humans or other predators
Other ground-dwelling birds on islands have suffered from the introduction of new predators by humans. On some UK islands rats have been eradicated to help puffins and other birds thrive as the rats eat the birds eggs and their young
Which of the following is not a reason some people argue we shouldn't bring species like the woolly mammoth back from extinction?
There aren't enough mammoth carcasses to recover DNA
Their habitat has changed and the mammoths will struggle to cope with global warming
There is no species large enough to carry a wooly mammoth foetus to term
Extinct animals are meant to be gone forever
Numerous species are candidates for de-extinction. A Pyrenean ibex kid was born in 2003 but died 7 minutes after its birth due to a lung defect. The last Pyrenean ibex had died in 2000 after being crushed by a falling tree
Passenger pigeons are an example of an extinct species. As a key part of the North American ecosystem they are a candidate for de-extinction. What is this process?
Genetically modifying an unrelated species to resemble an extinct species
Replacing the extinct species with another similar species
Removing some predators from the food chain to balance the loss of the extinct species
Cloning the species from the DNA of preserved specimens
In 1866, one flock of passenger pigeons measured a mile wide and 3.5 miles long, and contained an estimated 3.5 billion birds. The last individual died in 1914. Scientists will need to make thousands of individual birds before the population can be self-sustaining. These will need to be raised by other pigeon species, meaning they may act differently to the original species
Why did the early human ancestor species Homo erectus become extinct?
Homo erectus was outcompeted by the more aggressive Homo neanderthalensis
The ice age was too harsh for Homo erectus to survive
Homo erectus evolved into a different species
An outbreak of disease reduced the Homo erectus population to below functional numbers
Home erectus are our ancestors - they are believed to have evolved into the next step on our family tree
Which of the following is not commonly a reason for a species to go extinct?
New predators moving into or being introduced into an area
New disease is introduced to a population
Random mutation in DNA
Habitat loss and destruction
Mutation commonly occurs in a limited number of individuals rather than an entire species at once. If the mutation gives rise to a useful adaptation, it is more likely to be passed on to future generations as the individuals are more likely to survive longer and breed successfully
Which of the following is not a possible reason for a single mass extinction event?
Erupting volcanos
Over hunting
An ice age
Asteroid impact
Hunting normally impacts on a limited number of individuals and species in a particular area. A single global event affects a significant percentage of the world's species
Which of the following is a type of evidence used to show mass extinctions in the past?
Written records
Fossil record
Ice cores
Soil samples
The fossil record can show when large numbers of species vanished
What is speciation?
The destruction of a species
The evolution of a new species
Where a species splits into two or more sub-groups
The localisation and specialisation of a species
Speciation occurs when adaptations allow ecologically successful individuals to survive and breed, passing on characteristics not seen before in the species
Why might a new predator entering an area lead to extinctions?
The new predator will be looking for novel foods
A predator moving into a new area will kill off all the other predators in the area
New predators will encourage other predators to hunt in case they consume all the food resources
Native prey have no awareness or defences against the new threat
When humans arrived on various islands the animals living there had no fear of them and so could be rapidly hunted to extinction
How does evolution allow species to keep ahead of gradual climate change?
Adaptation at each generation allows them to make small gradual changes to keep up with climate change
The change in temperature will influence predator and prey equally
The change in the species will occur ahead of the change in the climate
Adaptation will occur to all the members of the species equally allowing them all to survive
One key point of the theory of evolution is that, for a species to adapt many more have to be born than will survive, allowing the best adapted to survive the changes. If a species is already under pressure, or under multiple pressures, climate change may be the final straw for that species
Author:  Ruth M

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