Question

Suppose a sliver of oceanic crust was discovered in the interior of a continent. Would this support or refute the theory of plate tectonics? Explain.

Short answer

The discovery supports the theory of plate tectonics by indicating past tectonic activity and plate movement.

Step-by-step solution

Understand the theory of plate tectonics

The theory of plate tectonics suggests that Earth's outer shell is divided into several plates that glide over the mantle. These plates can include oceanic crust, which is usually thinner and more dense, and continental crust, which is thicker and less dense. At plate boundaries, plates can diverge, converge, or slide past each other.

Identify the significance of oceanic crust in the context of plate tectonics

Oceanic crust is typically found at the bottom of ocean basins and is formed at mid-ocean ridges. It can be subducted under continental plates at convergent boundaries, often causing geological phenomena like earthquakes and volcanic activity. The presence of oceanic crust away from current plate boundaries can suggest past tectonic activity.

Recognize evidence for historical tectonic processes

Finding a sliver of oceanic crust in the interior of a continent can be seen as evidence of past tectonic activity. It could indicate that the area was once a location of a convergent boundary where oceanic crust was forced into or onto the continental crust, or an area where continents once split apart. This situation aligns with the concept of continental drift and the rearrangement of Earth's plates over geological time scales.

Interpret the evidence in terms of plate tectonics theory

The discovery of oceanic crust within a continent supports the theory of plate tectonics because it suggests that the crustal configuration has changed over time, consistent with the movement of tectonic plates. This remnant of oceanic crust indicates that an oceanic plate may have been subducted or accreted, providing evidence of the dynamic nature of plate interactions.

Key concepts

Oceanic Crust

Oceanic crust forms a significant part of Earth's outer layer and is mainly located beneath ocean basins. It is generally composed of basaltic rock, which is a dark, dense rock type. Oceanic crust is much thinner compared to continental crust, typically ranging from about 5 to 10 kilometers in thickness. In contrast, continental crust can be up to 70 kilometers thick in places.

The creation of oceanic crust occurs at mid-ocean ridges, where tectonic plates are pulling apart. As they separate, magma from the mantle rises to fill the gap, cools, and solidifies to form new crust. Over time, this continuous process gradually moves oceanic crust away from the ridge across the ocean floor. This movement is a key player in the process known as seafloor spreading.

• Thin and dense
• Found beneath oceans
• Recycled through subduction

Continental Drift

The concept of continental drift refers to the gradual movement of continents over Earth's surface. This idea was first put forth by Alfred Wegener in the early 20th century. He suggested that the continents were once part of a giant landmass called Pangaea and have slowly drifted apart to their current positions today.

Initially met with skepticism due to a lack of a satisfactory mechanism, continental drift is now understood within the framework of plate tectonics. It explains how continents can "drift" as they are part of larger tectonic plates that float on the semi-fluid asthenosphere beneath them. These plates interact at their boundaries, where they can pull apart, collide, or slide past each other.

Evidence supporting continental drift includes:

• Fossil records matching across continents
• Similar rock formations found on separate landmasses
• Continental shapes that fit together like puzzle pieces

Tectonic Activity

Tectonic activity encompasses all movements and interactions of the Earth's plates. It is responsible for shaping the landscape of our planet, creating mountain ranges, ocean trenches, and earthquakes. Activity is most pronounced at plate boundaries, where the huge blocks of Earth's crust known as tectonic plates collide, separate, or slide by one another.

There are three main types of plate boundaries, each causing different forms of tectonic activity:

• Divergent Boundaries: Plates pull apart, leading to the formation of new crust at mid-ocean ridges through seafloor spreading.
• Convergent Boundaries: Plates collide, often resulting in one plate being pushed beneath another, a process that can create powerful earthquakes and volcanic eruptions.
• Transform Boundaries: Plates slide past each other sideways, causing friction that can lead to earthquakes.

Overall, tectonic activity helps in recycling the Earth's crust and contributing to the constant evolution of its surface.

Subduction Zones

Subduction zones are regions where one tectonic plate sinks beneath another into the mantle. This process occurs at convergent boundaries where an oceanic plate typically subducts under a continental plate due to its higher density. Subduction is a key process in the recycling of the Earth's crust.

As the oceanic plate descends, it melts and may form magma. This magma can rise to the surface to create volcanic arcs parallel to the trench formed at the boundary. Such zones are also closely associated with deep ocean trenches, intense seismic activity, and volcanic eruptions.

Important characteristics of subduction zones include:

• Deep ocean trenches
• Volcanic arcs
• High earthquake activity

This process significantly shapes the geological features on Earth and supports the theory of plate tectonics by illustrating the dynamic movements and interactions of the Earth's crustal plates.