Throughout the history of the planet, there has been an evolution and flux of species. From the first microorganisms found in the ocean billions of years ago, to the evolution of land-based plants, invertebrate and vertebrate animals, reptiles, mammals, and to the millions of species we now know of today. Historically, the earth has experienced five mass extinction events. These have been linked to some sort of natural disturbance where three-quarters of all species were lost over a short geological period. Glaciation events, volcanic eruptions, and asteroid impacts are theorized to be the cause of these five mass extinctions.
Recently, some scientists hypothesized that the earth is undergoing a sixth extinction event linked to the evolution of human civilization. This theory suggests that over the course of human history, people have caused the extinction of species on a massive scale. As humans became more civilized, we began altering the environment to fit our needs. We altered the land for agricultural uses; as our tools became more advanced, we were able to hunt more efficiently on land and in water; we built cities, and have extracted resources from the earth in ways never done before. These alterations and interactions with the environment have led to the loss of habitats, overexploitation of animals, and caused irreversible loss of the earth’s organisms.