The Great Oxygenation Event

Description:  The Great Oxygenation Event occurred when cyanobacteria living in the oceans started producing oxygen through photosynthesis. As oxygen built up in the atmosphere anaerobic bacteria were killed leading to the Earth's first mass extinction. The change in diversity and the arrival of appreciable atmospheric oxygen (as evidenced by the red bands in the rocks) can be analyzed to see what happens when a resource that was scarce becomes very abundant.

Web Resource: Great Oxygenation Event - Wikipedia

The Asteroid That Killed The Dinosaurs

Description:  It is estimated that 75% of plant and animal (including dinosaur) species went extinct after the Earth was hit with a massive asteroid 66 million years ago. Evidence includes a thin layer of rock containing iridium (rarely found on Earth but common in asteroids) around the planet. Scientists have also discovered a large impact crater. The cause of the extinction is fairly clear but the details of the effects leave much to be explored.

Web Resource:  Cretaceous–Paleogene extinction event - Wikipedia

Galapagos Finch Evolution

Description:  When Darwin visited the Galapagos Island he collected a number of bird species that he brought back to England. He presented them to ornithologist John Gould thinking they were a variety of birds and he was told that they were all different varieties of finches. This led Darwin to speculate that a population of finches had arrived on the islands and had adapted to different climates through natural selection. However Darwin was never able to observe evolution taking place. Researchers Peter and Rosemary Grant have been observing evolution of Galapagos finches for the last 40 years. One of the most famous studies involved the change in beak depth of medium ground finches during times of drought. Birds that had small beaks were unable to open the dry seeds causing microevolution in the surviving birds.

Web Resources:  Peter and Rosemary Grant Research - Wikipedia, The Beak of the Finch - HHMI