Introduction

There is predicted to be nearly 10 million unique species around the globe. There are so many different species, and scientists think that this only represents less then 1% of species that have ever lived. That means 99% of past species have gone extinct. Today, hundreds are getting closer and closer to extinction each year because of causes like the environment, things we humans do, natural selection, and changes in the environment over time. Scientists have recorded more than 500 species that have gone extinct since we started counting them. Just think about how many have become extinct throughout the entire world.

The U.S. passed the Endangered Species Act (ESA) in 1973 in order to protect those plant and animal species that are at risk of becoming extinct. Species that receive protection under the ESA are classified into two categories, "Endangered" or "Threatened," depending on their status and how severely their survival is threatened. A species that is listed as Endangered is in danger of becoming extinct throughout a significant portion of its habitat range. We also sometimes categorize species as critically endangered when they are in imminent danger of extinction. Threatened species are those that are likely to become Endangered in the foreseeable future.