The properties of rocks and minerals reflect the processes that formed them.
Waves, wind, water, and ice shape and reshape Earth's land surface.

Rocks on the Earth’s surface are continually broken down by chemical and physical processes. Rainwater is slightly acidic because it contains dissolved carbon dioxide from the air. This weak acidity can chemically cause rocks to break apart and dissolve. Physical processes such as grinding by glaciers, pounding by waves, the freezing/thawing of water in ice cracks, and the growth of roots also break rocks into smaller pieces. Weathering is the technical term for both the chemical and physical processes that naturally break rocks.

While most people associate the term erosion with the breaking of rocks, technically erosion refers only to the movement of rock material from one location to another. Erosion eventually transports broken rock to the ocean as sediment. The net effect of this erosion is to lower the surface of the continents to sea level. From the point of view of geological time, mountains crumble rapidly. In the course of just 18 million years, the continents would be reduced to sea level and the oceans would cover the entire planet.

Why do we still have continents and mountains that reach miles into the air? Since the continents have existed for hundreds of millions of years, weathering and erosion must be balanced by a mountain building process. This process, known as plate tectonics, forms an important part of Grade 6 science standards.

For Grade 4, we set the stage for the later learning of mountain building. We introduce minerals and rocks (Standards 4a and 4b), and some of the processes that form igneous and metamorphic rock (Standard 4a). These processes and the rapid geologic events of earthquakes and volcanoes (Standard 5a) directly relate to plate tectonics.

The order in which the standards were written does not imply that they are supposed to be taught in that sequence. As in all the strands, these standards can be taught in many ways and in many sequences. The concept map below provides one way to organize these standards. The wording of some of the standards has been slightly changed for space reasons and to emphasize a particular conceptual flow.