8th Grade Science Videos & Lessons. Try it free.

Elements are pure substance made of only 1 type of atom. Each element has properties that can be used to identify it. All elements are arranged in rows and columns on the periodic table.

When substances undergo chemical reactions their properties change. The total number of atoms does not change throughout a chemical reaction. Scientists use chemical reactions to create new materials and medicines.

Human population has increased dramatically over the past 2 centuries. An increasing population can strain our natural resources. Humans can make decisions or use technology to reduce our impact on Earth.

Biodiversity describes the number of different kinds of organisms in an ecosystem. Scientists measure biodiversity to determine an ecosystem's health. Humans depend on healthy ecosystems for food, medicine and clean water.

Fossils are evidence of past life, such as bones, teeth, and footprints. The collection of fossils in the Earth's crust and their placement in chronological order is called the fossil record. Scientists study the fossil record to understand how life on Earth has changed over time.

Climates are the result of the unequal heating and cooling of the Earth. Circulation of the atmosphere moves a lot of thermal energy around the globe. Circulation of water in the ocean (ocean currents) can also influence regional climates.

Scientists study rock layers to understand Earth's history. In a series of rock layers, the oldest ones are the bottom and the newest one are at the top. Scientists organize Earth's 4.6 billion year history through the geologic time scale.

Bacteria are living things made of only one cell. Viruses can't reproduce on their own so they hijack cells to make copies of themselves. Our immune system eliminates most bacteria and viruses.

Humans have changed the genes of living things by breeding for thousands of years. Biotechnology is when we use our knowledge of biological process to solve problems. We use products improved with biotechnology everyday from detergents to medicines.