Step 1: Earth Summit Overview
The Earth Summit, also known as the United Nations Conference on Environment and Development (UNCED), took place in Rio de Janeiro, Brazil, in 1992. The summit was a major event in global environmental governance, focusing on sustainable development and addressing the growing environmental concerns of the time.
Step 2: Analyzing the Options
- (A) 1988: Incorrect. The Earth Summit was not held in 1988.
- (B) 1992: Correct. The Earth Summit was held in 1992. It marked a significant moment in international environmental policy and discussions about sustainable development.
- (C) 1997: Incorrect. The Earth Summit did not take place in 1997, though other significant environmental agreements happened in subsequent years.
- (D) 1999: Incorrect. By 1999, no such summit took place. The Earth Summit was specifically in 1992.
Step 3: Conclusion
The correct year when the Earth Summit (UNCED) was held is 1992.
\[
\boxed{\text{Correct Answer: (B) 1992}}
\]