Rheic Ocean

The Rheic Ocean was a major body of water during the Paleozoic Era. It separated two massive landmasses known as paleocontinents. One landmass was Gondwana, which sat near the south pole. The other was Laurussia, made of Laurentia, Baltica, and Avalonia. This ocean played a vital role in shaping the Earth's surface. Its eventual closure helped create the supercontinent Pangaea. Today, we can still see its history in the Earth's crust. Its sutures, or scars from land collisions, stretch from Mexico to Turkey.

The ocean formed through a specific geodynamic process. At the start of the Paleozoic, about 540 million years ago, Gondwana dominated the southern hemisphere. A volcanic arc called the Cadomian orogeny existed on Gondwana's northern edge. This occurred as oceanic crust subducted, or sank, below the continent. Eventually, a mid-oceanic ridge subducted at an oblique angle. This caused extensional basins to develop along the northern margin of Gondwana. These basins evolved into a rift, which is a long crack in the crust.

This rift eventually became a mid-oceanic ridge. This ridge acted as a divider between landmasses. It separated small fragments like Avalonia and Carolina from Gondwana. As these fragments drifted north, the Rheic Ocean began to form in the Early Ordovician. The ocean continued to grow as these pieces moved. It reached its maximum width during the Silurian period. During this same time, the older Iapetus Ocean was closing. The collision of Avalonia-Carolina with Laurentia created the Appalachian orogeny.

The name of the ocean comes from Greek mythology. It was named after Rhea, who was the sister of Iapetus. This naming follows the pattern of the Iapetus Ocean. The Iapetus Ocean was the predecessor to the modern Atlantic Ocean. The Rheic Ocean existed from the Early Ordovician until the Early Carboniferous. It was a defining feature of the ancient world's geography. The name connects the ancient oceans to the myths that inspired their naming.

The closure of the Rheic Ocean was a massive event. This process began in the Early Devonian period. It was completed during the Mississippian period. The closure happened because Gondwana and Laurussia collided. This collision resulted in the assembly of the supercontinent Pangaea. This event also triggered several large orogenies, which are mountain-building events. These include the Variscan and Alleghanian orogens. These formed between Gondwana's West African margin and southern Baltica. They also involved eastern Laurentia. Additionally, the Ouachita orogeny formed between the Amazonian margin of Gondwana and southern Laurentia.

Changes in the ocean also impacted the history of life. During the Silurian, the Prague Basin sat in the Rheic Ocean. This basin was an archipelago of humid volcanic islands. These islands were located on the outer edges of the Gondwanan shelf. The islands became a major hotspot for plant biodiversity. This happened during the early stages of the Silurian-Devonian Terrestrial Revolution. The rapid environmental changes from volcanic activity helped plants diversify. High rates of endemism, or species found nowhere else, likely drove this growth.

The closing of the ocean may have also changed marine life. This happened alongside the start of the Late Palaeozoic Ice Age. These combined factors may have sparked a major evolutionary event. This is known as the Carboniferous-Earliest Permian Biodiversification Event. This event saw a massive radiation of marine species. Specifically, there was an increase in the richness of fusulinids and brachiopods. The movement of the continents and the changing climate created new opportunities for life to flourish in the seas.