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 plate tectonics, illustrating past tectonic activity.

Step-by-step solution

Understanding Plate Tectonics

The theory of plate tectonics suggests that the Earth's outer shell is divided into several plates that glide over the mantle. Oceanic and continental crusts are part of these plates, and their movements explain the formation of mountains, earthquakes, and ocean trenches.

Examine Oceanic Crust in Continental Interiors

Oceanic crust is typically found at the bottom of ocean basins due to its denser material. Finding it inside a continent might initially seem unusual because it challenges the traditional idea of ocean crust only being submerged under oceans.

Examine Historical Plate Movements

According to plate tectonics, plates move over geological time. This movement can lead to oceanic crust being pushed onto continents, a process known as obduction or being part of accretionary wedges from ancient oceanic ridges.

Interpret Findings in Relation to Plate Tectonics

The presence of oceanic crust in continental interiors can actually support plate tectonics, as it may have arrived there through past tectonic activity, such as subduction-related processes or ancient collisions that pushed oceanic material onto the continental plate.

Key concepts

Oceanic Crust

Oceanic crust forms the solid outer shell beneath the world's oceans. It is predominantly composed of basalt, which is denser than the materials found in continental crust. This characteristic density causes it to sit lower, effectively making it the bedrock of ocean basins. Oceanic crust is relatively thin, usually only 5-10 kilometers thick. It is continuously created at mid-ocean ridges, where tectonic plates diverge and magma rises to cool and solidify. As new crust forms, the older crust spreads outward and moves away from the ridge. Over time, this leads to a recycling process, with some oceanic crust being pushed into the mantle at subduction zones. Key features of oceanic crust include:

• Dark, dense basaltic composition
• Formation at mid-oceanic ridges
• Part of the dynamic cycle of creation and subduction

Understanding oceanic crust is crucial in explaining phenomena such as earthquakes, volcanic activity, and the creation of new ocean floor.

Continental Crust

The continental crust is the thick layer of rock that forms the continents and the areas of shallow seabed close to their shores. Unlike the oceanic crust, continental crust is mainly composed of lighter, less dense granite rocks. This makes it thicker, averaging about 30 to 50 kilometers. Continental crust is less dense, so it "floats" higher compared to oceanic crust. This results in continents rising above sea level. Composed largely of granite, it is older and more complex, containing some of the oldest rocks on Earth, dating back billions of years. Notable aspects of continental crust include:

• Composition of lighter granitic rocks
• Greater thickness compared to oceanic crust
• Formation and preservation of ancient geological history

As a crucial part of Earth's surface, the continental crust plays a major role in supporting life, shaping topography, and influencing climate.

Geological Time

Geological time refers to the vast span of time over which Earth's geological developments have occurred. It covers billions of years, from Earth's formation to the present day. This expansive timescale allows scientists to understand the slow yet dynamic processes shaping our planet. These include the movement of tectonic plates, the gradual buildup of mountain ranges, and the shifting of oceanic and continental crust. The major divisions of geological time are organized into eons, eras, periods, epochs, and ages. Radiometric dating helps date rocks and fossils, providing evidence for these time divisions. Important aspects to consider:

• Represents Earth's 4.5 billion-year history
• Key to understanding the slow processes of plate tectonics
• Aids in dating rocks and understanding Earth's evolutionary history

By looking at geological time, we gain insight into Earth's ever-changing nature and learn how past events have shaped the world we live in today.

Obduction

Obduction is the geological process where oceanic crust is thrust onto the edge of a continental plate. It is somewhat the opposite of the more common subduction, where oceanic crust is drawn beneath a continental plate into the mantle. Obduction occurs when tectonic forces cause the oceanic crust to crash into and be pushed over the stronger and denser continental crust. This process can result in the formation of mountain ranges and unique rock formations as parts of the ocean floor are elevated above sea level. Key characteristics include:

• Uplifting of oceanic crust onto continental land
• Formation of ophiolites, which are slices of oceanic crust and upper mantle
• Demonstrates tectonic interactions and supports plate tectonic theory

Understanding obduction helps explain many geological features seen today and provides supporting evidence for the theory of plate tectonics.