Three jobs for sunlight

The idea

The ozone layer absorbs most short-wavelength UV; visible light reaches the surface, powering photosynthesis and partly warming land and water; infrared warms the surface, which re-radiates heat that greenhouse gases partly trap.

Different rays, different work

Sunlight is a mix of ultraviolet, visible and infrared radiation.

Does each kind do the same job on the Earth?

• No, each has its own role
• Yes, all do the same job
• Only one kind does anything

What each one does

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Three kinds, three roles

Ozone takes in most of the short wavelength UV. Visible light gets down to the ground and feeds plants. Infrared warms the ground, and the ground sends heat back up.

The ozone layer absorbs most short-wavelength UV. Visible light reaches the surface, powering photosynthesis and partly warming land and water. Infrared warms the surface, which re-radiates heat that greenhouse gases partly trap.

Notes

Ozone absorbs most UV. Visible light feeds photosynthesis and partly warms land and water. Infrared warms the surface, and greenhouse gases partly trap the heat it re-radiates.

Check yourself

What mostly absorbs short wavelength UV radiation?

Which radiation gives the energy for photosynthesis?

Which radiation warms the Earth's surface, which then re-radiates heat?

Which gases trap a part of the heat that the surface re-radiates?

• The ozone layer — correct. Yes!
• The oceans. The chapter says the ozone layer in the upper atmosphere mostly absorbs short wavelength UV.
• The soil. Short wavelength UV is mostly absorbed by the ozone layer in the upper atmosphere, before it reaches the soil.
• Ultraviolet. UV is mostly absorbed by the ozone layer. Visible light reaches the surface and powers photosynthesis.
• Visible light — correct. Yes!
• Radio waves. Radio waves carry very little energy. Visible light powers photosynthesis.
• Ultraviolet. UV is mostly absorbed by the ozone layer in the upper atmosphere.
• Gamma rays. Gamma rays are mostly filtered by the upper atmosphere, so they do not warm the surface.
• Infrared — correct. Yes!
• Greenhouse gases such as CO₂, CH₄ and water vapour — correct. Yes!
• The ozone layer, which absorbs UV. The ozone layer absorbs UV. The gases that trap outgoing heat are greenhouse gases.
• Visible light, which reaches the surface. Visible light is radiation from the Sun. It is not a gas that traps heat.