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Paragraph A: **Tropical rainforests** are among the world’s most crucial and complex ecosystems. Despite covering less than **6%** of the Earth’s land surface, they harbor **over half** of the world’s plant and animal species. They are frequently referred to as the “**Lungs of the Earth**” because of their essential role in regulating global oxygen and carbon dioxide levels. This regulation is achieved through the process of **photosynthesis**, where trees absorb atmospheric $\text{CO}_2$ and release $\text{O}_2$.

Paragraph B: The structure of the rainforest is defined by distinct vertical layers. The highest layer is the **emergent layer**, where tall trees can reach heights exceeding **60 meters**. Below this is the **canopy**, a **dense, interlocking roof** formed by the branches and leaves of most trees. This canopy intercepts up to **95%** of the sunlight, creating a perpetually dark and humid environment in the layers below. The understory consists of smaller trees and shade-tolerant plants, while the final layer is the **forest floor**, where decomposition occurs rapidly due to the **high temperature and moisture**.

Paragraph C: The high **biodiversity** found in rainforests is the result of millions of years of stable, warm, and wet conditions. The **Amazon rainforest**, the largest in the world, covers approximately **5.5 million square kilometers** and plays a vital role in regional weather patterns by recycling large volumes of water vapor back into the atmosphere—a process called **evapotranspiration**.

Paragraph D: However, these vital ecosystems are under severe threat, primarily from **deforestation** driven by logging, cattle ranching, and agricultural expansion. Satellite monitoring confirms that rainforests are being cleared at alarming rates. For instance, between **2000 and 2012**, the world lost an area of forest roughly the size of Angola. Preserving these ecosystems is now a global environmental priority, not just for the species they contain, but for the fundamental role they play in maintaining the planet’s **climate balance**.