What is population explosion?

Explanation

### Step-by-Step Solution:

1. **Definition of Population Explosion**:
- Population explosion refers to a rapid increase in the population density of a species, particularly humans. It indicates a situation where the growth rate of the population exceeds the carrying capacity of the environment.

2. **Historical Context**:
- The human population has experienced significant growth over the past century. For instance, the world population was approximately 2 billion in 1900 and surged to about 6 billion by the year 2000. This represents a tripling of the population in just 100 years.

...