Seafloor spreading happens at divergent plate boundaries under the ocean. As hot rocks rise in convection currents within the asthenosphere, they push the tectonic plates above them apart. The top of the convection current heats the crust above it and melts some of the rock, so it becomes magma. As the tectonic plates pull away from each other at the divergent plate boundary, the magma fills in the space between them. When the magma cools, it becomes basalt and forms new oceanic crust.
Seafloor Spreading and Continental Drift
Seafloor spreading could have explained Alfred Wegener’s continental drift theory, but in 1912, we didn’t know anything about the ocean floor. It wasn’t until sonar was developed during World War I that people could explore deep under the waves. Sonar technology improved during World War II, and in 1953, Marie Tharp and Bruce Heezen, two American geologists, created the first maps of the floor of the Atlantic Ocean.
Tharp and Heezen’s map included the Mid-Atlantic Ridge, a 10,000 mile stretch of the larger Mid-Ocean Ridge that stretched through the middle of the Atlantic Ocean. It looked like a mountain range full of ridges and valleys at the bottom of the ocean.
Tharp and Heezen’s discovery inspired Harry Hess, a Navy geologist, to revisit his work from World War II. During the war, Hess worked as a Navy submarine commander. Part of his assignment was to study the ocean floor. In 1962, he explained that seafloor spreading was caused by magma coming up through the Mid-Ocean Ridges and pushing the plates on either side apart.
Evidence for Seafloor Spreading
Hess had three important pieces of evidence to support his seafloor spreading theory. First, rocks near the Mid-Atlantic Ridge were much younger than rocks near the continents. Second, bands of rocks extending away from the ridge showed alternating polarity of the Earth’s magnetic field. Basalt, the primary rock of the ocean floor, contains magnetite, a magnetic mineral. When basalt forms, it aligns with the direction of the Earth’s magnetic field. The Earth’s magnetic field changes regularly, so the alternating magnetic polarity of the rocks suggested that they formed at different times in Earth’s history. Finally, heat sensors showed that the area around the Mid-Atlantic Ridge was much hotter than the rest of the ocean.
Each part of the Mid-Ocean Ridge separates at a different speed. The Mid-Atlantic Ridge is pulling apart slowly, about one inch per year. Because it is moving slowly, the rocks have cracked, creating massive ridges and valleys. The East Pacific Rise, located about 2,000 miles off the coast of South America, is separating much faster at about four inches per year. As a result, it forms a smoother mountain range under the ocean. As these mid-ocean ridges grow, they push the tectonic plates around them apart, causing the continents to move.
HOW TO REMEMBER WHAT YOU LEARN
Now that you have learned about seafloor spreading, it is time to focus on remembering what you have learned. The first part of remembering is paying attention. Next, make sure you take the time to process what you learn. You can do this by answering comprehension questions, creating a mind map, drawing a picture, or talking about what you learned.
Next, you need to practice remembering what you have learned. My favorite tool for practicing remembering is flashcards. Flashcards are easy to make and force our brains to try to remember the answers to questions because when our brain sees a question, it attempts to answer it. So just trying to answer the question and then seeing the right answer will help you strengthen your neural networks on the topic.
Finally, if you are taking a test on a topic, make sure you study for about ten minutes a day for several days before the test. Then, the night before the test, get a good night’s sleep. Sleeping will help your brain clean itself and strengthen neural networks. Pulling an all-nighter may seem like a good idea, but it is terrible for your brain. Finally, while taking the test, take deep breaths to stay calm, and always go with your first instinct unless you can prove why your later guess is right. You are more likely to change a right answer to a wrong answer than the other way around.
ARE YOU LEARNING ABOUT ANOTHER SCIENCE TOPIC?
Do you want to learn about more than seafloor spreading? I am always creating more science units so that every science student can get exactly what they need to understand science. Click on the pictures below to check out other science topics that will help you understand how the world around us works.
MORE SCIENCE RESOUCES
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