Question

Each phrase below describes a vocabulary term from the list. Write the term that matches the phrase describing it. Theory proposed by Harry Hess that includes processes along mid-ocean ridges

Short answer

Sea-Floor Spreading.

Step-by-step solution

Understanding the Theory's Origin

Harry Hess was a geologist whose work in the mid-20th century contributed significantly to the field of plate tectonics. He proposed a theory to explain the movement of the Earth’s lithospheric plates.

Identifying Key Concepts of the Theory

Hess's theory centers around the concept of mid-ocean ridges, which are underwater mountain ranges. He suggested that new oceanic crust is formed at these ridges due to seafloor spreading.

Matching the Concept to the Vocabulary List

Since the theory involves processes occurring specifically at mid-ocean ridges where the seafloor spreads and new crust is formed, the term that matches this description is 'Sea-Floor Spreading.'

Key concepts

Harry Hess

Harry Hess was an influential geologist whose groundbreaking theories shaped our understanding of plate tectonics. During the mid-20th century, his research led to the formulation of the sea-floor spreading theory. This theory became a critical component in explaining how ocean basins grow and reform over geological timescales.
Hess proposed that the Earth's lithosphere, which includes the crust and the upper mantle, is divided into large tectonic plates that move over the more fluid asthenosphere beneath. His insights were initially based on sonar mapping of the ocean floor, which revealed surprising topographic features like mountain ranges and deep trenches.

• He introduced the idea that mid-ocean ridges are sites of continuous volcanic activity.
• Notably, his work was central to understanding how new oceanic crust is created along these ridges.
• His contributions laid the groundwork for the modern theory of plate tectonics.

Through his pioneering work, Hess revolutionized how geologists understood the dynamic nature of the Earth's surface.

mid-ocean ridges

Mid-ocean ridges are underwater mountain ranges that snake across the ocean floor. They are formed by plate tectonic processes and serve as the site for seafloor spreading. Hess's observations of these ridges were crucial in formulating his theory of sea-floor spreading.
These ridges are characterized by a central rift valley, from which magma rises to create new oceanic crust. This process is continuous, adding layers to the ocean floor and pushing existing plates apart. As the plates move apart, what we can see is the beginning of ocean basins expanding.
Key features of mid-ocean ridges include:

• Ridges run for thousands of kilometers, making them the Earth's longest mountain range.
• They have a central rift valley created by tectonic plates pulling apart.
• Magma from Earth's mantle emerges at these ridges, solidifying into new crust.
• The constant creation of new crust here makes these regions geologically dynamic.

Understanding mid-ocean ridges is crucial to comprehending the broader picture of plate tectonics and oceanic crust formation.

plate tectonics

The theory of plate tectonics describes the large-scale movements of Earth's lithosphere, which is divided into tectonic plates. This concept is fundamental to modern geology and provides the framework for understanding phenomena such as earthquakes, volcanic activity, and mountain-building.
The lithosphere is made up of plates that float on the semi-fluid asthenosphere below. Movements and interactions of these plates can create different geological features and events. The motion of these plates over time shapes continents and oceanic regions.

• Key processes include seafloor spreading, subduction, and continental drift.
• Plates can move away from each other, towards each other, or slide past each other.
• Interactions of tectonic plates lead to the formation of mountains, ocean trenches, and mid-ocean ridges.

This theory was further established by Hess's work, providing a coherent explanation for the mechanism driving the movement of Earth's plates.

oceanic crust

The oceanic crust is the outermost layer of Earth beneath the ocean basins. It is primarily composed of basalt, which is a dense, mafic rock. Oceanic crust is continually created at mid-ocean ridges and is part of the dynamic cycle described by the theory of plate tectonics.
New oceanic crust forms as magma rises from beneath the Earth at mid-ocean ridges and cools. As more magma solidifies, it pushes the older crust away from the ridges, leading to the process known as seafloor spreading.

• This crust is thinner and denser than continental crust.
• It has an average thickness of about 7 kilometers.
• Oceanic crust ages and eventually gets recycled back into the mantle through subduction.

The creation and destruction of oceanic crust are vital for understanding not only the increasing size of ocean basins but also the tectonic processes that shape our planet's surface over millions of years.