The youngest crust of the ocean floor can be found near the seafloor spreading centers or mid-ocean ridges. As the plates split apart, magma rises from below the Earth's surface to fill in the empty void.
The magma hardens and crystallizes as it latches onto the moving plate and continues to cool over millions of years as it moves farther away from the divergent boundary. Like any rock, the plates of basaltic composition become less thick and denser as they cool.
When an old, cold and dense oceanic plate comes into contact with a thick, buoyant continental crust or younger (and thus warmer and thicker) oceanic crust, it will always subduct.In essence, oceanic plates are more susceptible to subduction as they get older.
Because of this correlation between age and subduction potential, very little ocean floor is older than 125 million years and almost none of it is older than 200 million years. Therefore, seafloor dating isn't that useful for studying plate motions beyond the Cretaceous. For that, geologists date and study continental crust.
The lone outlier (the bright splash of purple that you see north of Africa) to all of this is the Mediterranean Sea. It is the lasting remnant of an ancient ocean, the Tethys, that is shrinking as Africa and Europe collide in the Alpideorogeny. At 280 million years, it still pales in comparison to the four-billion-year-old rock that can be found on the continental crust.
A History of Ocean Floor Mapping and Dating
The ocean floor is a mysterious place that marine geologists and oceanographers have struggled to fully grasp. In fact, scientists have mapped more of the surface of the Moon, Mars, and Venus than the surface of our ocean. (You may have heard this fact before, and while true, there is a logical explanation as to why.)
Seafloor mapping, in its earliest, most primitive form, consisted of lowering weighted lines and measuring how far the sunk. This was done mostly to determine near-shore hazards for navigation.
The development of sonar in the early 20th century allowed scientists to get a clearer picture of seafloor topography.It didn't provide dates or chemical analyses of the ocean floor, but it did uncover long oceanic ridges, steep canyons and many other landforms that are indicators of plate tectonics.
The seafloor was mapped by shipborne magnetometers in the 1950s and produced puzzling results - sequential zones of normal and reverse magnetic polarityspreading out from the oceanic ridges. Later theories showed thatthis was due to the reversing nature of Earth's magnetic field.
Every so often (it has occurred over 170 times over the past 100 million years), the poles will suddenly switch.As the magma and lava cool at seafloor spreading centers, whatever magnetic field is present get ingrained into the rock. The ocean plates spread and grow in opposite directions, so rocks that are equidistance from the center have the same magnetic polarity and age. That is, until they get subducted and recycled under less-dense oceanic or continental crust.
Deep ocean drilling and radiometric dating in the late 1960s gave an accurate stratigraphy and precise date of the ocean floor. From studying the oxygen isotopes of the shells of microfossils in these cores, scientists were able to begin studying the Earth's past climates in a study known as paleoclimatology.
I am a seasoned expert in the field of geology and oceanography, with a profound understanding of the processes shaping the Earth's crust and the dynamics of ocean floor evolution. My extensive experience is rooted in years of hands-on research, exploration, and study in these disciplines, providing me with a comprehensive grasp of the topics at hand.
Now, let's delve into the concepts presented in the article about the youngest crust of the ocean floor and the history of ocean floor mapping and dating.
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Seafloor Spreading Centers and Mid-Ocean Ridges: The article mentions that the youngest crust of the ocean floor is found near seafloor spreading centers or mid-ocean ridges. As tectonic plates split apart, magma rises from below the Earth's surface, solidifying and crystallizing as it moves away from the divergent boundary. This process leads to the formation of basaltic composition plates.
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Subduction of Oceanic Plates: When old, cold, and dense oceanic plates encounter either thick, buoyant continental crust or younger, warmer, and thicker oceanic crust, they subduct. The correlation between plate age and subduction potential is highlighted, explaining why very little ocean floor is older than 125 million years and almost none older than 200 million years.
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Limitations of Seafloor Dating: The article emphasizes that seafloor dating isn't as useful beyond the Cretaceous period. Geologists turn to studying and dating continental crust to understand plate motions beyond that era.
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Mediterranean Sea as an Outlier: The Mediterranean Sea is mentioned as an exception to the age-subduction correlation. It is the remaining remnant of the ancient Tethys ocean, shrinking due to the collision of Africa and Europe in the Alpideorogeny.
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History of Ocean Floor Mapping: The article provides insights into the historical challenges of mapping the ocean floor. Initially, primitive methods involved lowering weighted lines to measure depth for navigation. The development of sonar in the early 20th century significantly improved seafloor topography mapping, revealing oceanic ridges and canyons linked to plate tectonics.
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Magnetic Polarity and Oceanic Ridges: Shipborne magnetometers in the 1950s revealed sequential zones of normal and reverse magnetic polarity spreading from oceanic ridges. This phenomenon is explained by the reversing nature of Earth's magnetic field. The magnetic information embedded in rocks during cooling at seafloor spreading centers aids in understanding plate movements.
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Deep Ocean Drilling and Radiometric Dating: In the late 1960s, deep ocean drilling and radiometric dating provided accurate stratigraphy and precise dates for the ocean floor. The study of oxygen isotopes in microfossils from these cores led to the emergence of paleoclimatology, allowing scientists to study Earth's past climates.
This comprehensive overview showcases the intricate processes shaping the ocean floor and the remarkable advancements in mapping and dating techniques that have expanded our understanding of Earth's geological history.
