Brine pools, known as underwater lakes or lakes of death, are extreme, salty pockets in the ocean. They are so salty and lack oxygen that marine animals avoid them. If a fish or crab falls in, the salty water disrupts their cells, stopping movement and breathing quickly. Scientists study these pools for clues about early Earth and life in harsh conditions. These pools form when very salty water gathers in deep ocean spots. In the Red Sea, brine comes from dissolved ancient salt deposits. These pools can be 3 to 8 times saltier than usual seawater and contain no oxygen. This creates a clear, visible boundary between the brine pool and surrounding water. Globally, brine pools exist mainly in the Gulf of Mexico, Mediterranean Sea, and the Red Sea. The Orca Basin in the Gulf of Mexico has the deepest known pool at 2,200 meters deep, eight times saltier than normal seawater. Animals entering brine pools face instant fatal effects. The high salt draws water rapidly from their cells, and without oxygen, they cannot breathe. Animals die or get stunned within seconds, creating underwater graveyards of their remains. Yet predators like shrimp use the brine’s edge as hunting grounds, waiting to catch stunned animals. Though deadly to large animals, brine pools thrive with special microbes that live without oxygen and sunlight. These microbes survive on chemical energy and form thick mats. Marine scientist Sam Purkis says, “At this great depth, there is ordinarily not much life on the seabed. However, the brine pools are a rich oasis.” Some fish and shrimp use the brine boundary to hunt, feeding on animals caught in the salty trap. These microbes mirror early Earth conditions when life first appeared, helping scientists explore how life survives without oxygen. They also have potential medical uses, with some microbes producing antibacterial and anticancer compounds. The Red Sea shines globally for its many brine pools—at least 25 known locations. Recently, researchers discovered new pools just 2 kilometers from Saudi Arabia’s coast in the Gulf of Aqaba, much closer than before. The biggest measures 260 by 70 meters. Lack of oxygen in these pools preserves sediment layers without disturbance. Such layers hold records of rainfall, floods, earthquakes, and tsunamis going back over 1,000 years. Purkis explains these are ‘‘natural time capsules’’ offering rare geological and environmental histories. Brine pools remain a focus for science due to their deadly power, unique life forms, and historical value. They show how life can survive harsh earths and reveal the ocean’s hidden depths.