Final answer:
The environment immediately surrounding an undersea hydrothermal vent is extreme and characterized by hot, chemical-rich water filled with minerals. It supports a thriving ecosystem of organisms adapted to this environment.
Step-by-step explanation:
The environment immediately surrounding an undersea hydrothermal vent is best described as extreme. These vents release hot, chemical-rich water filled with minerals, creating an environment that is toxic, high in temperature, and under high pressure. However, despite these harsh conditions, the vent supports a thriving ecosystem of organisms adapted to this environment.