Shanghai Edition - Junior High School Science, Grade 8, Semester 1: Earth's 'Protective Outer Layer': Composition and Vertical Stratification

The Life Shield of the Atmosphere: More Than Just Gas, It’s Protection

As a geographer, we must first understand: the atmosphere is not a uniform 'blanket.' It serves as the Earth's life system'sbarrier and buffer zone. The lower atmosphere consists ofdry clean air, water vapor, and solid impurities suspended in the atmospherethree components. Among them,ozoneabsorbs ultraviolet radiation, protecting organisms from harmfulsolar radiationradiation.

Figure 2-1-1 Schematic Diagram of Atmospheric Vertical Stratification (Simplified)

The Mystery of the Three-Layer Structure

Troposphere: Contains three-quarters of the atmospheric mass and nearly all water vapor. Physical laws are extremely strict:temperature drops by 6°C for every 1,000 m increase in altitude. This uneven heating causes violent air turbulence, forming clouds, rain, and snow.
Stratosphere:temperature increases with altitude. Here, ozone absorbs ultraviolet radiation and releases heat. As air moves predominantly horizontally, the atmosphere is extremely stable—ideal for commercial aircraft cruising.
Upper Atmosphere: Here, theionospherecan reflect radio waves. As shown in Figure 2-1-2, Radio Wave Propagation Diagram, it acts as a natural 'relay tower' enabling long-distance radio communication.

The presence of the atmosphere not only provides breathable air, but itsinsulating effect on the surfacealso reduces day-night temperature differences, providing a stable greenhouse environment for all life on Earth. The atmosphere is Earth's strongest yet gentlest 'outer garment'.

QUESTION 1

Which atmospheric component primarily absorbs solar ultraviolet radiation and is known as Earth’s 'protective umbrella'?

Nitrogen

Oxygen

ozone

Water vapor

QUESTION 2

If a mountain peak is 2,000 meters higher than its base, according to the vertical temperature variation rule in the troposphere, how much lower is the peak temperature compared to the base?

6°C higher

6°C lower

12°C lower

12°C higher

QUESTION 3

What is the primary reason why temperature in the stratosphere increases with altitude?

Carbon dioxide absorbing ground radiation

Ozone absorbing large amounts of solar ultraviolet radiation

Farther from the ground, so less affected by ground radiation

Extremely high atmospheric density in this layer

QUESTION 4

Which of the following statements about the troposphere is incorrect?

Weather phenomena vary greatly

Atmospheric mass accounts for about 3/4 of total mass

Temperature increases with height

Water vapor and solid impurities are concentrated here

QUESTION 5

Long-distance radio wave communication relies primarily on which part of the atmosphere?

Troposphere

Stratosphere

ionosphere

Ozone layer

Comprehensive Case Study: Atmospheric Detection and Vertical Stratification

Analyze the impact of different atmospheric layers on human activities

Explorer Zhang Qiang plans to climb Mount Everest, while simultaneously, a commercial airliner flies at 10,000 meters above him. We will use this real-life scenario to analyze the structural characteristics of the atmosphere.

1. Based on differences in vertical temperature change, how many main layers does the atmosphere have, and what are their characteristics?

Answer:
The atmosphere is mainly divided into three layers: (1) Troposphere: temperature decreases with increasing altitude, convection is significant, and weather phenomena are frequent. (2) Stratosphere: temperature increases with altitude, the atmosphere is stable, skies are clear, and it contains the ozone layer. (3) Upper Atmosphere: extremely low air density, containing the ionosphere capable of reflecting radio waves.

2. In which layer do weather phenomena like rain, snow, and lightning occur? In which layer is it ideal for aircraft flight?

Answer:
Complex weather phenomena such as rain, snow, and lightning all occur in the troposphere, where nearly all water vapor and impurities are concentrated. Aircraft are best suited for flying in the stratosphere, where horizontal airflow dominates, visibility is high, and air currents are stable.

3. What is the impact of the upper atmosphere on human activities?

Answer:
The upper atmosphere contains the ionosphere, which reflects radio shortwaves, enabling long-distance radio communication across Earth. Additionally, it is the space where artificial satellites orbit and auroras occur.

4. Interpret the diagram: During the day, at the same altitude near the surface, how do atmospheric pressures over oceans and land differ? Where is pressure higher, and where is it lower?

Answer:
During the day, land warms quickly, resulting in higher temperatures and rising heated air, creating low pressure at the surface. The ocean warms slowly, maintaining relatively lower temperatures, causing air to sink and forming high pressure at the surface. Thus, near the surface, oceanic pressure is higher than land pressure.

5. Continuing from the previous question, how does pressure distribution at a certain height above the ground compare to that at the surface? How does it differ at night?

Answer:
At a certain height above the ground, pressure distribution is opposite to that at the surface (high pressure over land, low pressure over ocean). At night, this reverses completely: land cools rapidly, forming high pressure, while the ocean cools slowly, forming low pressure—laying the foundation for learning about thermal circulation in the next lesson.