The atmosphere is the gases around Earth, held by gravity. Air has mass and therefore weight, and its molecules exert pressure in all directions. Air generally gets thinner with height. Almost all familiar weather occurs in the lowest layer, the troposphere. Ozone higher up absorbs much harmful ultraviolet radiation; greenhouse gases also help keep Earth warm. Safety: No pressure experiment or direct observation of the Sun. These values are not health or altitude advice. Stop: Stop after the paper model. No suction, sealed containers, balloons, pressure devices, altitude trips, or Sun viewing.

Materials: Paper; Pencil; Ruler 1. Draw Earth’s surface as a line at the bottom of the page. Above it draw two bands: Troposphere, lowest layer; Stratosphere, above it. Write Not to scale because layer thickness varies. Add a cloud and rain symbol only in the lowest band as examples of familiar weather. 2. Inside a small square labelled Imaginary air sample, draw dots for molecules and arrows toward each of the four walls. Label Pressure acts in all directions. Add Gravity gives air weight beside a downward arrow outside the square. Keep weight and pressure arrows distinct. 3. Copy illustrative height-pressure cards: Low site: 100 pressure units; middle site: 80 units; high site: 60 units. Sort by height and draw three bars. Mark Invented units; pattern only, not an altitude calculator. 4. Add two protection/function labels: stratospheric ozone absorbs much harmful UV; greenhouse gases absorb and emit infrared and help keep Earth warmer. Explain why these functions are different. Finish: Most weather is in __; the atmosphere is not a hard lid. Done: A two-layer diagram, molecule/pressure square, three sorted pressure bars, and two distinct atmosphere functions are complete. Proof: Keep the sheet. Note help with graph scale, molecule arrows, or distinguishing UV from infrared. Stop: Stop after the paper model. No suction, sealed containers, balloons, pressure devices, altitude trips, or Sun viewing.