Mid-ocean ridges form when tectonic plates meet beneath the ocean and ridge-push, slab-pull or do both to create a subduction zone. Over time, one plate raises up. This, along with the simultaneous magma buildup, creates a submarine mountain range, or ocean ridge.
When tectonic plates meet, they are essentially unstoppable forces, which means something must give. Usually, one plate slides beneath the other, lifting the edge of the second plate, creating a subduction zone. As the subduction zone grows, magma seeps in through the cracks and edges of the plate, quickly cooling as it hits the surface. These underwater actions have raised tall mountain range systems totalling about 37,000 miles in length altogether.
Around the ridge, the cracks and gaps that allow magma to escape also allow ocean water to seep in. When it meets the deep-earth magma, it picks up heavy metals conveyed up from the earth's core, such as gold and iron. The super-heated, mineral-rich water then returns through hydrothermal vents at temperatures up to 700 degrees Fahrenheit. The sudden shock of hitting cold ocean water causes minerals to precipitate out quickly, creating rich ore deposits and supporting the habitats of deep-ocean microbes. These microbes, in turn, provide a food source for tubeworms, shrimp and mussels, creating a strange ecosystem that could not exist without the mid-ocean ridge's hydrothermal vents.