Sea Floor Spreading Theory : Before reading the theory let us know some basics:
The Seafloor spreading theory, proposed by geophysicist Harry H. Hess in 1960, explains a phenomenon occurring at mid-ocean ridges. Here, new oceanic crust is generated through volcanic activity and gradually moves away from the ridge. The theory is rooted in the observation that the age of seafloor rocks has varied over time.
Before delving into the intricacies of Seafloor Spreading, a solid understanding of foundational concepts such as Ocean Floor Mapping, the distribution of earthquakes and volcanoes, the Convectional Current Theory, and Paleomagnetism is essential.
The lithosphere constitutes the solid, outer segment of the Earth, encompassing the brittle upper section of the mantle and the crust, which forms the outermost layers of the Earth’s structure. Positioned between the atmosphere above and the asthenosphere (another component of the upper mantle) below, the lithosphere plays a crucial role in Earth’s geological framework.
A tectonic plate, also referred to as a lithospheric plate, is a substantial and irregularly shaped slab of solid rock that typically incorporates both continental and oceanic lithosphere. This geological structure is appropriately named a tectonic plate, encompassing the rocky elements of both the ocean floor and continents. These plates play a fundamental role in the Earth’s dynamic processes, influencing phenomena such as continental drift and the creation of geological features.
Sea Floor Spreading
Seafloor spreading is the divergence of tectonic plates, particularly oceanic plates, caused by the upwelling of molten magma from the Earth’s mantle. This process occurs at mid-ocean ridges, such as the Mid-Atlantic Ridge. Mantle convection, driven by heat transfer from the core to the surface, creates a convection current. Pressurized magma rises, cracks the ocean floor, and forms new seafloor as it cools. At divergent plate boundaries, oceanic plates separate, creating space for the rising magma.
The older ocean crust farther from the ridge is denser and sinks, creating a subduction zone. This process leads to the formation of mountains and uplands on the seafloor. As new crust forms along mid-ocean ridges, rocks closer to the ridge are younger, contributing to age variations. Additionally, seafloor spreading influences sea levels by increasing the ocean basin volume, decreasing sea levels as denser oceanic crust moves away from shallow mid-ocean ridges.
Evidence of seafloor spreading
- Similarities Along Oceanic Ridges: Rocks on both sides of the oceanic ridge crest, equidistant from the crest, exhibit similarities in terms of constituents, age, and magnetic orientation.
- Age Disparity of Oceanic and Continental Crust: Rocks in the oceanic crust near ridges are notably younger than those in the continental crust.
- Enhanced Temperature Gradient Near Ridges: The standard temperature gradient on the seafloor is 9.4° C/300 m, but it increases near ridges, indicating an upwelling of magma from the mantle.
- Shallow Earthquake Foci at Mid-Oceanic Ridges: Earthquake foci in mid-oceanic ridge areas are generally at shallow depths, contrasting with the deep-seated earthquakes along the Alpine-Himalayan belt and the Pacific rim.
What problems did Seafloor’s spreading theory solve?
- Seafloor spreading solved the problem of finding younger age rocks at mid-oceanic ridges and older rocks as we move away from the middle part of the ridges.
- It also explained why the sediments at the central parts of the oceanic ridges are relatively thin.
- The sea-floor spreading also proved the drifting of continents as propounded by Alfred Wegener and helped in the development of the theory of plate tectonics.
It was the first complete hypothesis to discuss seafloor movement and development. Morgan, along with other scholars including McKenzie and Parker, produced a more thorough understanding of the movement of distinct parts of the earth crust and related information in 1960. Plate tectonics is the theory that will explain it in detail.