Understanding Earth's Temperature and the Atmosphere

The question asks us to evaluate three statements about the Earth's atmosphere and its effect on temperature. Let's analyze each statement carefully.

• Statement I: Without the atmosphere, temperature would be well below freezing point everywhere on the Earth’s surface.
• Statement II: Heat absorbed and trapped by the atmosphere maintains our planet’s average temperature.
• Statement III: Atmosphere’s gases, like carbon dioxide, are particularly good at absorbing and trapping radiation.

Analysis of Statement I: Temperature Without Atmosphere

This statement suggests that the Earth's surface temperature would be significantly colder without its atmosphere. The atmosphere acts like a blanket, trapping some of the heat radiated by the Earth back into space. Without this effect, the Earth's temperature would drop drastically, likely averaging well below the freezing point of water. Planets or moons without substantial atmospheres, like the Moon, experience extreme temperature fluctuations between day and night and have very low average temperatures. Therefore, Statement I is correct.

Analysis of Statement II: Atmosphere Maintains Average Temperature

This statement describes a key role of the atmosphere: maintaining the planet's average temperature. The process involves certain gases in the atmosphere absorbing and re-emitting thermal radiation from the Earth's surface. This trapped heat prevents rapid cooling and keeps the average temperature within a range that supports life as we know it. This phenomenon is known as the greenhouse effect. Thus, Statement II is also correct.

Analysis of Statement III: Role of Greenhouse Gases like Carbon Dioxide

This statement identifies specific atmospheric gases, such as carbon dioxide, as being effective at absorbing and trapping radiation. These gases, often called greenhouse gases, have molecular structures that allow them to absorb infrared radiation (heat) emitted by the Earth. This absorption and subsequent re-emission in all directions, including back towards the surface, is what causes the trapping effect described in Statement II. Carbon dioxide, methane, water vapor, and nitrous oxide are examples of such gases. Therefore, Statement III is correct.

Conclusion on the Statements

Based on the analysis, all three statements accurately describe the role of the atmosphere and specific atmospheric gases in influencing Earth's temperature. Statement I highlights the cold conditions without an atmosphere, Statement II explains how the atmosphere maintains average temperature through heat trapping, and Statement III identifies the property of greenhouse gases like carbon dioxide responsible for this trapping.

Therefore, statements I, II, and III are all correct.

Revision Table: Earth's Atmosphere and Temperature

Additional Information: Understanding the Greenhouse Effect

The greenhouse effect is a natural process essential for life on Earth. Here’s a bit more detail:

• Solar radiation from the Sun reaches Earth. Most of this radiation is in the form of visible light.
• About 30% of the solar radiation is reflected back into space by clouds, ice, snow, and the Earth's surface.
• The remaining radiation is absorbed by the Earth's surface and the atmosphere, warming the planet.
• The warmed Earth's surface emits radiation primarily in the form of infrared radiation (heat).
• Greenhouse gases in the atmosphere absorb this infrared radiation.
• These gases then re-emit the infrared radiation in all directions, including back towards the Earth's surface.
• This process of absorption and re-emission traps heat within the lower atmosphere, raising the Earth's average temperature.

Without greenhouse gases, the Earth's average surface temperature would be around $-18^\circ\text{C}$ ($0^\circ\text{F}$), which is well below freezing. The natural greenhouse effect raises this average temperature to about $15^\circ\text{C}$ ($59^\circ\text{F}$), making the planet habitable.