Question

The Tethys Ocean was once global. Today, it has completely disappeared except in the eastern Mediterranean Sea and the Black Sea. Do you think there was more oceanic crust when the Tethys was a global ocean?

Short answer

Yes, there was more oceanic crust when the Tethys Ocean was global.

Step-by-step solution

Understanding the Tethys Ocean

The Tethys Ocean was a vast body of water that existed during the Mesozoic Era, separating the continents of Gondwana and Laurasia. It was a significant portion of the global marine environment of that time.

Defining Oceanic Crust

Oceanic crust is the part of Earth's lithosphere that surfaces in ocean basins. It is thinner but denser than continental crust and forms at mid-ocean ridges as molten magma cools and solidifies.

Analyzing Historical Presence

When the Tethys was a global ocean, it naturally spanned a larger area. This implies that there was a substantial extent of oceanic crust underpinning it at that time.

Examining Present-Day Geography

Currently, remains of the Tethys Ocean are found only in the eastern Mediterranean Sea and the Black Sea, indicating a significant reduction in area. The oceanic crust here is now less extensive than it once was.

Concluding the Comparison

Given that the Tethys Ocean was once wide and global compared to its current reduced geographic remnants, it can be inferred that there was indeed more oceanic crust in the past when it covered a broader area.

Key concepts

Mesozoic Era

The Mesozoic Era is a fascinating chapter in Earth's geological history, often referred to as the "Age of Reptiles" due to the dominance of dinosaurs. This era spans approximately 180 million years, from 252 to 66 million years ago, and is divided into three periods: the Triassic, Jurassic, and Cretaceous. It was a time of significant geological and biological change. During the Mesozoic, the supercontinent Pangaea began to break apart, leading to the formation of new ocean basins and the drifting of continents.
As continents divided, new ecosystems emerged, creating diverse environments for life to evolve. The climate during the Mesozoic Era was generally warmer than today, with high sea levels and no polar ice caps. This warm climate contributed to the creation of shallow seas, which were home to a wide variety of marine life, including the vast Tethys Ocean. The era ended with the Cretaceous-Paleogene extinction event, which led to the extinction of many species, including the dinosaurs.

oceanic crust

Oceanic crust plays a pivotal role in understanding Earth's surface dynamics. It is a type of crustal material that makes up the oceanic part of Earth's lithosphere and covers about 60% of the planet's surface. Unlike continental crust, oceanic crust is thinner (about 5 to 10 kilometers thick) but denser, primarily composed of basalt, a type of volcanic rock. This density makes it heavier and responsible for its tendency to be subducted under continental crust.
Oceanic crust is constantly being created at mid-ocean ridges, where tectonic plates pull apart, allowing magma to rise, cool, and solidify to form new crust. This process is part of the plate tectonics cycle, which also includes the recycling of crustal material back into the mantle via subduction zones.
The youthful age of oceanic crust—generally no older than 200 million years—reflects its continuous regeneration and recycling, which contrasts starkly with continental crust that can be billions of years old.

continental drift

Continental drift is the gradual movement of Earth's continents over its surface—a concept first proposed by Alfred Wegener in the early 20th century. Originally met with skepticism, this theory was later validated by the development of plate tectonics in the mid-20th century. Continental drift explains how continents shift position on Earth's surface due to tectonic plate movements.
This movement is caused by the immense forces generated by the convection currents within the Earth's mantle, which push and pull the plates. Over millions of years, these movements lead to the opening and closing of ocean basins, mountain formation, and even climatic changes. The movement of continents is responsible for the past presence of the Tethys Ocean, which existed between the drifting land masses of Gondwana and Laurasia.
Understanding continental drift helps explain the distribution of fossils, climatic patterns seen in the geological record, and the alignment of mountain ranges across different continents.

mid-ocean ridges

Mid-ocean ridges are underwater mountain systems formed by plate tectonics—essentially the seams of Earth's crust where new oceanic crust is born. They are the most extensive mountain ranges on Earth, stretching across 65,000 kilometers globally. These ridges are characterized by a central rift valley, where the floor of the ocean is actively spreading apart.
This process, known as seafloor spreading, occurs as tectonic plates diverge, allowing magma to rise from the mantle, cool, and crystallize into new oceanic crust. Mid-ocean ridges are characterized by typical volcanic and seismic activity due to the continuous creation of new crust, an essential part of Earth's geological cycle. They play a crucial role in the recycling of Earth's crust by spreading the plates apart and later contributing to the subduction of older crustal areas.
Their role in Earth's past is underscored by the spread of the Tethys Ocean, which expanded across what is now the Mediterranean and surrounding regions due to the activity at mid-ocean ridges.