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Unlock This CourseImagine pulling apart a piece of stretchy dough - as you pull, it gets thinner and eventually breaks apart. This is exactly what happens at divergent plate boundaries, where Earth's tectonic plates move away from each other. These boundaries are like giant cracks in the Earth's surface where new crust is constantly being created.
Divergent boundaries are some of the most active geological areas on our planet. They're responsible for creating new ocean floor, forming spectacular underwater mountain ranges and even splitting continents apart over millions of years.
Key Definitions:
At divergent boundaries, convection currents in the mantle pull tectonic plates apart. As the plates separate, hot magma rises from below to fill the gap. This magma cools and solidifies, creating new crust. The process is continuous, constantly adding new material to the Earth's surface whilst pushing the plates further apart.
There are two main types of divergent boundaries, each creating different geological features depending on whether they occur in oceanic or continental crust.
These occur beneath the ocean and are the most common type of divergent boundary. They create mid-ocean ridges - massive underwater mountain chains that stretch for thousands of kilometres across the ocean floor.
These underwater mountains can rise 2-3 kilometres above the surrounding seafloor. The Mid-Atlantic Ridge, for example, runs down the centre of the Atlantic Ocean like a giant underwater spine.
Constant volcanic activity occurs along these ridges as magma erupts to form new oceanic crust. The newest rock is always found at the ridge centre, with older rock further away.
Hot water springs on the ocean floor where seawater meets hot volcanic rock, creating unique ecosystems with specialised marine life.
When divergent boundaries occur within continents, they create rift valleys - long, narrow depressions in the land surface. If the rifting continues, it can eventually split a continent apart and create a new ocean basin.
The East African Rift is a perfect example of a continental divergent boundary in action. This massive crack in the Earth stretches over 3,000 kilometres from the Red Sea to Mozambique. The African plate is slowly splitting into two parts - the Nubian plate and the Somali plate. Over millions of years, this rift may become a new ocean, separating East Africa from the rest of the continent. The rift contains several large lakes, including Lake Victoria and Lake Tanganyika and is home to many active volcanoes.
Divergent boundaries create distinctive geological features that help scientists identify and study these areas. Understanding these features is crucial for marine science as they significantly impact ocean environments and marine ecosystems.
Scientists can measure the age of oceanic crust and find that it gets progressively older as you move away from mid-ocean ridges. This provides strong evidence for seafloor spreading and helps us understand how fast plates are moving - typically 2-10 centimetres per year.
Mid-ocean ridges aren't perfectly straight lines. They're broken up into segments by transform faults - fractures that run perpendicular to the ridge. These faults allow different sections of the ridge to spread at slightly different rates, accommodating the curved nature of Earth's surface.
When magma erupts underwater at mid-ocean ridges, it cools rapidly in the cold seawater, forming distinctive pillow-shaped rocks called pillow lavas. These rounded formations are a clear indicator of underwater volcanic activity.
The Mid-Atlantic Ridge is the longest mountain range on Earth, stretching about 10,000 kilometres from the Arctic to the Southern Ocean. It runs right down the middle of the Atlantic Ocean, separating the European and African plates from the North and South American plates. The ridge is spreading at about 2.5 centimetres per year, which means the Atlantic Ocean is getting wider whilst the Pacific Ocean shrinks. Iceland sits directly on the Mid-Atlantic Ridge, making it one of the few places where you can actually see a mid-ocean ridge above sea level. The island is volcanically active because of its position on this divergent boundary.
Divergent boundaries have a profound impact on marine ecosystems and ocean chemistry. The constant creation of new seafloor and volcanic activity creates unique environments that support specialised forms of marine life.
One of the most fascinating discoveries in marine science has been the unique ecosystems around hydrothermal vents at mid-ocean ridges. These underwater hot springs support communities of organisms that don't rely on sunlight for energy - instead, they use chemosynthesis to convert chemicals from the vents into food.
Giant tube worms up to 2 metres long live around vents, hosting bacteria that convert chemicals into energy.
Specialised crabs and other crustaceans have adapted to the extreme conditions around hydrothermal vents.
Several species of fish have evolved to live in the warm, chemical-rich waters around vents.
Divergent boundaries play a crucial role in the rock cycle by creating new igneous rock from magma. This process is fundamental to understanding how Earth's crust is constantly renewed and recycled.
The magma that erupts at mid-ocean ridges is typically basaltic - a dark, dense igneous rock that forms the foundation of oceanic crust. This basalt is rich in iron and magnesium, giving it its characteristic dark colour and high density.
As new oceanic crust forms at mid-ocean ridges, it records the direction of Earth's magnetic field at the time of formation. Since Earth's magnetic field reverses periodically, this creates a pattern of magnetic stripes on either side of the ridge - providing further evidence for seafloor spreading.
The ocean floor is much younger than the continents. Whilst some continental rocks are billions of years old, the oldest oceanic crust is only about 200 million years old. This is because oceanic crust is constantly being created at divergent boundaries and destroyed at convergent boundaries, making it part of a continuous recycling process.
Scientists use various methods to measure how fast plates are moving at divergent boundaries. GPS technology now allows us to measure plate movement with incredible precision - sometimes down to millimetres per year.
Satellites, underwater robots and deep-sea drilling have revolutionised our understanding of divergent boundaries. Scientists can now map the ocean floor in detail and study the processes happening at these remote locations in real-time.
Understanding divergent plate boundaries is essential for marine science because these areas are where new ocean floor is born. They influence ocean circulation patterns, create unique habitats for marine life and help us understand the dynamic nature of our planet. From the formation of new islands to the creation of the deepest parts of our oceans, divergent boundaries are truly where Earth shows its creative power.