The Endangered Species Act of 1973 was passed.

The purposes of this Act are to provide a means whereby the ecosystems upon which endangered species and threatened species depend may be conserved, to provide a program for the conservation of such endangered species and threatened species and to take such steps as may be appropriate to achieve the purposes of the treaties and conventions set forth…

—Endangered Species Act of 1973, Section 2

An endangered species is any species of plant or animal that has become so rare that it is in danger of becoming extinct. Extinction occurs when there are no more members of that species still alive. Extinction happens for a number of reasons. Sometimes, the climate changes, either gradually or due to a sudden event, and a species unable to cope with the change becomes extinct. Such is believed to have been the case with the dinosaurs, which disappeared (along with a large number of other species) 65 million years ago, in an event known as the Cretaceous Extinction. The prevailing theory is that a large meteor struck the Earth near the Yucatan Peninsula in Mexico, causing a huge dust cloud that lowered the world’s temperature for many years. In other cases, human activity can cause species to become threatened, endangered or extinct. Sometimes, the reasons are indirect, such as habitat encroachment or pollution, and sometimes the causes are quite direct, as when a species is hunted by man to the point where it cannot sustain itself and eventually dies off. Both habitat encroachment and over-hunting are considered to be the causes of the extinction of the passenger pigeon, a species once found in North America in large numbers. The Endangered Species Act was passed in an effort to address some of these issues. In some cases, this type of legislation and other similar efforts can be quite successful, as was seen in the dramatic recovery of the bald eagle, a species once threatened by pollution. In other cases, the Endangered Species Act has come into conflict with the needs of people, especially in the areas of farming, irrigation and building. Efforts are being made to change aspects of the Endangered Species Act, in the hopes of creating balance between a number of competing concerns. As with so many of the complex issues of domestic policy, many of the issues associated with the Endangered Species Act continue to be hotly debated.

Science NetLinks
Science NetLinks offers a series of two lessons on endangered species.

The first lesson, Endangered Species 1: Why Are Species Endangered? (6–8), introduces and explores the various issues and problems faced by endangered species globally.

In the second lesson in the series, Endangered Species 2: Working to Save Endangered Species (6–8), students view an online presentation about endangered species, then role-play a debate about spotted owl protection from the point of view of lumber workers, environmental activists and government and scientific interests.

EconEdLink
In the lesson If You Hear a Hoot, Then This Site Is Kaput (9–12), students examine the work of special interest groups regarding the Endangered Species Act as they try to answer questions such as: Should the Endangered Species Act of 1973 be left alone so the legal system is left to decide the toughest cases? Should the Endangered Species Act of 1973 be revised in order to increase economic growth without endangering listed species? Can this even happen?

In Eco-terrorism in Vail, CO (9–12), students explore choices and their consequences while learning about an act of eco-terrorism committed by the Earth Liberation Front on October 20, 1998, in the ski village of Vail, Colorado. Students examine alternative views of the Vail expansion that prompted the eco-terrorism, explore the role of incentives in environmental management and discuss alternative, non-violent solutions to the problem of habitat encroachment.

Xpeditions
Postcards From the Edge: Endangered Species (6–8) helps students learn about endangered species in the United States, some of the reasons they are endangered (e.g., habitat destruction or the introduction of invasive species) and what is being done to protect them. Students choose one species to focus on and examine the reasons it is endangered and why it is important to make an effort to save it.

In Why Preserve Biodiversity? (6–8), students discuss the importance of maintaining ecosystems and find out about the various arguments that people make in favor of preserving the Earth's biodiversity.

In Preservation Is Important? Says Who? (3–5), students learn about National Geographic Emerging Explorer Mark Olson's efforts to identify extinct or nearly extinct plants and consider the issues surrounding conservation efforts in a variety of contexts.

In Preservation Issues: Competing Interests (6–8), students consider the issues surrounding conservation efforts in a variety of contexts, compare the perspectives of those who are most intensely involved in both wildlife conservation and agriculture and form an opinion as to what might be done to reconcile their conflicting priorities. Students will research two sides of a specific issue and construct arguments supporting specific viewpoints.

ReadWriteThink
In Investigating Animals: Using Nonfiction for Inquiry-based Research (K–2), students research animals with nonfiction and informational material. Through their research, they learn how to document their discoveries. They work together to question, research, investigate and share their findings.

In Listen, Look and Learn: An Information Gathering Process (K–2), primary students work together as a class group to seek for information on the sloth. They gather information from teacher-presented material and on the Internet, and organize the information on an "information wheel." This technique can be used for gathering information on a variety of animals, endangered or otherwise.

Illuminations
In the late 19th century, the gray whale was hunted to near extinction, but it was finally given protection by the International Whaling Commission in 1946. Although most countries have agreed to abide by an international ban on whaling, Japan and Norway continue to hunt whales for commercial use. In the unit Representing Data (Pre-K–8), students at different age levels use various math skills to solve real-world problems. The activity for grades 7 and 8 is a calculation of the weight of gray whales by using estimation.