Many scientists study objects and events that they cannot observe directly. But through extensive sampling, observation, and analysis, scientists are able to construct a plausible series of explanations to describe subjects ranging from the birth of our solar system to the lives of extinct creatures. For example, paleontologists work to unravel the stories of our past through the collection and analysis ... Full description.

This article discusses how scientists' efforts to explain paleoclimate evidence have produced some of the most significant theories of how the Earth's climate system works. Topics include Earth's shifting orbit, and evidence of ancient climates preserved in geologic strata, ocean cores, coninental ice sheets, and tree rings. Full description.

This animation shows two views of a pendulum swinging over the North Pole. A drawing shows the path traced out by the swinging pendulum which when traced out over time, the orientation of the plane appears to change. This provides evidence for Earth's rotation because it shows that Earth is rotating underneath the unchanging orientation of the pendulum's swing. Full description.

This activity has students read and answer questions based upon the article 'The plate tectonic story: a scientific jigsaw.' The article starts with the continental drift theory of Alfred Wegener and adds the evidence from the seafloor to arrive at plate tectonics. It concludes with remarks about mantle dynamics and the future ability to predict earthquakes. Full description.

Early evidence showing striking similarities between regions on opposite sides of vast oceans suggested that in Earth's distant past what are now separate continents may once have been connected. However, this evidence said nothing about how the continents could have moved to their present positions. This video shows how seafloor spreading creates new oceanic crust and how the crust is destroyed by ... Full description.

This activity has students apply scientific theory and hypothesis to studies being conducted in the Black Sea. They will discuss the purpose of and theory behind the Black Sea study and use maps to explain the flood theory. Students will also write hypotheses suggesting what certain pieces of evidence might reveal about the Black Sea and the flood. Next, they will read about the researchers' discoveries ... Full description.

This reference provides instructions on how to write scienctific reports. Topics include why we write reports, the basic format (introduction, methods and materials, results, and discussion, or 'IMRaD'), how to state a hypothesis, how to set up tables, graphs and figures, and how to write a discussion. There are also links to additional information, including a sample report, and a list of books on ... Full description.

A common criticism of natural selection is: How can it produce novel complex useful structures by pure random chance? Darwin argued that selection is not a random process, and furthermore, it is cumulative. This lesson provides a way for students to actually compare the cumulative non-random selection of Darwin with the non-cumulative version so often erroneously implied. Students attempt to produce ... Full description.

This page provides an introduction to plate tectonics for secondary students. Topics include plate motions, the layers of the Earth and oceanic versus continental plates. A set of links provides access to material on the processes of plate tectonics occuring at plate boundaries, zones of movement and instability. Full description.

At this site the question of the extinction of the dinosaurs takes the form of an interactive matrix. With the hypotheses in the left margin and the types of evidence along the bottom, the resulting squares are indicated in cases where the evidence supports the hypothesis. Students can click on hypotheses to view an animated description, click on an evidence element to get a definition, or click on ... Full description.