Extinction

• Scientists currently estimate that there are only 8.7 million species of organisms are alive today
• Extinction


  The permanent loss of all the members of a species
• How evolution takes place

  1. New species evolve that are better suited to survive the new conditions

  2. Older species that cannot cope with the change gradually die out because they are not able to compete so well for food and other resources
• Some of the species that have become extinct are lost forever or only exist in the fossil record, while other species have descendants living on Earth today
• Causes of extinction


  • Change in temperature
  • New predators
  • New diseases
  • New, more successful competitors
  • Changes to the environment over geological time
  • Single catastrophic events, such as volcanic eruptions or collisions with asteroids
• Ways living organisms can cause extinction

  • New predators can wipe out unsuspecting prey animals
  • New diseases can bring a species to the point of extinction
  • One species can cause another to become extinct by successful competition
• The biggest influences on survival are changes in the environment
• Throughout history, the climate and environment of the Earth has been changing
• Organisms that do well in the temperature of a tropical climate wouldn't do well in the freezing conditions of an Ice Age
• Changes to the climate or the environment have been the main cause of extinction throughout history
• There have been five occasions during the history of the Earth when significant climate change has led to extinction on an enormous scale
• Fossil evidence shows that at times there have been mass extinctions on a global scale
• A single catastrophic event is often the cause of these mass extinctions, such as a colossal volcanic eruption or the collision of giant asteroids with the surface of the Earth
• The most recent mass extinction was when the dinosaurs became extinct around 65 million years ago
• What destroyed the dinosaurs

  1. A giant asteroid collided with the Earth in Chicxulub in Mexico

  2. The asteroid impact would have caused huge fires, earthquakes, landslides, and tsunamis

  3. Enormous amounts of material would have been blasted into the atmosphere, making everywhere almost dark

  4. Plants struggled to survive and the drop in temperatures caused a global winter

  5. Between 50 and 70% of all living species, including dinosaurs, became extinct
• There is a group of UK scientists who suggest that the extinction of the dinosaurs started sooner (137 million years ago) and that it was much slower than previously thought
• Their theory is that the melting of the sea ice (caused by global warming) flooded the seas and oceans with very cold water, triggering the mass extinction
• Building up a valid, evidence-based history of events that happened so long ago is not easy to do, as events can always be interpreted in different ways
• It will be a very long time before there is enough evidence for scientists to be completely sure about the extinction of the dinosaurs