and Scope of the Problem
This question in Earth Science Explorer allows students to examine Earth as a system. They can compare it to other systems--for example, other planets. Using astronomy, they can relate Earth to all other bodies in the solar system, including asteroids and comets. Collisions with these types of bodies might have contributed to extinctions.
We can also learn much about Earth through remote sensing platforms, such as the Magellan and Galileo probes to Venus and Jupiter and Earth-orbit satellites.
Viewing Earth as a system helps reveal how it serves as a home for diverse live. This approach also enables us to see many interrelationships, like those among Earth proceses and features and those between life and physical environments. To focus our attention on Earth as a system, we examine Earth's spheres (atmosphere, hydrosphere, etc.). You can best explain Earth by taking your students through the spheres as they are now and as they have been. In the process you reveal the agents of change that affect our planet in the long and short term. You also show the special nature of Earth that makes it different from the other planets.
Dinosaur extinction works as a perfect start for our investigation. The dinosaurs (more than 440 genera have been discovered) existed for millions of years. They must have been well adapted to life on Earth, yet they ultimately perished. Their story is one of both success and failure to occupy this home.
We tell students that most of Earth's life forms are extinct. Estimates are sketchy, but possibly 99.9 percent of all life forms in Earth's history are extinct. Also, the average life span for a species is about 4 million years, according to paleontologist David Raup. Current humans are classified as a subspecies, Homo sapiens sapiens. Once students understand the basic concepts of species and extinction, ask, "How long will this particular subspecies last?" and "What might cause this subspecies to become extinct?" The causes of extinction for other species might affect our own.