Seafloor Spreading

Introduction

Seafloor spreading is a natural geologic process that separates large tectonic plates from the Earth’s lithosphere. The theory of sea flooring shows that new oceanic crust is formed between older rocks at mid-ocean ridges as older rocks move away from the mid ridge while the younger ones tend to stay closer to the mid ridge. Other related processes include paleomagnetism, convection current theory and evidence of seafloor spreading. 

Ocean floor mapping

Mapping the ocean floor helps in contextualizing the processes mentioned above. There are mountains, ridges and even volcanoes inside the ocean. The oceanic rocks are relatively older than continental rocks. The equidistant rocks from the mid-oceanic range also have similar ages and chemical and magnetic properties. 

Convection current theory

Convection current theory is one of the prominent reasons behind the discovery of seafloor spreading. Arthur Holmes, in the 1930s, was the first one to identify convection currents in the mantle generated by the radioactive elements causing thermal differences. 

According to the current convection theory, the heat generated in the mantle needs a place to escape. The rising limbs of the currents escape through the lithosphere and form oceanic ridges by breaking into older rocks. 

In other words, the rising limbs lead to divergence of the lithospheric plates forming new oceanic ridges, while the falling limbs lead to the convergence of the oceanic plates forming a deep ocean trench. The movement of the trench is also widely dependent on the movement of the mantle inside the Earth’s crust. 

Palaeomagnetism

Palaeomagnetism is defined as studying the Earth’s magnetic fields. The polarity and reversal nature of the Earth’s magnetic field can be studied from rocks of different ages. Rocks or oceanic ridges are formed under the sea bed due to seafloor spreading. These rocks are called Basaltic because they have low silica and iron content. 

 As the rocks get solidified, the magnetic elements inside them align themselves parallelly with the direction of the magnetic field. Studies have also proven that the orientation of the Earth’s magnetic field follows a geomagnetic reversal or frequently alternates with time. 

Concept of seafloor spreading

Harry Hess was the first to introduce the concept of seafloor spreading. In his research, he conveyed that when oceanic plates diverge, Magma arising from the Earth’s interior causes tensional stress which leads to fractures in the lithosphere. The basaltic Magma rises to the ocean floor, forming a rock-like structure as it cools down. The process is carried into the future; hence, older rocks move far away from the mid ridge while the younger ones stay closer. 

Evidence for seafloor spreading

• The first and foremost proof for seafloor spreading is the equal distance between the rocks on both sides of the mid-oceanic ridge. 
• Secondly, the age of the rocks is also quite similar, adding strong proof to the research. 
• The rocks closer to the oceanic ridge are also relatively younger when compared to the rocks near the continental crust. 
• The average temperature at the sea bed is 9 degrees celsius. In contrast, the temperature near the oceanic ridge is comparatively higher indicating the upward movement of the magnetic materials and lava. 

Evidence from magnetic stripes

Oceanic ridges are formed due to the upward movement of the molten lava and magnetic materials. It has also been proven that oceanic ridges are nothing but magnetic stripes. The Earth is like a giant magnet with North and South poles. The Earth’s magnetic poles can reverse themselves. During that time, the compass needle would point South. The geomagnetic reversal of the rocks is strong evidence of the reversal of the Earth’s magnetic field.

As the molten material historically transformed into  rock, the iron inside settled along with the Earth’s magnetic field. The formation of ridges took place accordingly like tiny needles in cement. Rocks with similar ages had similar magnetic memory, hence proving the research behind seafloor spreading.  

Evidence from molten material

In the late 1960s, a team of scientists decided to study the formation of oceanic ridges; hence they built a small submersible ship that could withstand  crushing pressure while moving down into the ocean. 

The scientists decided to dive four kilometers into the ocean floor of Alvin and they found strange rocks shaped like pillows or toothpaste when squeezed, which can only happen when something too hot (Molten material) gets hardened or solidified. 

Conclusion

Seafloor spreading is a natural geologic process that separates large tectonic plates from the Earth’s lithosphere. The evidence behind seafloor spreading supports continental drift theory. This evidence is provided from magnetic stripes as well as molten material.