Sometimes the sea goes down.
The water leaves the land. New land shows up. This can happen when it gets very cold. It changes how things live. Do you like the beach?
{
"text": "Sometimes the sea level goes down.
This is called a regression. The water leaves the seafloor. This makes new land appear. \n\nThis can happen during ice ages. Much water turns into ice. Then there is less water in the sea. \n\nMoving land can also change the sea. Large pieces of land can join together. This makes the ocean basins bigger. \n\nWhen the sea goes down, it changes life. Some sea animals may die out. This has happened many times in history. \n\n
Sometimes the sea level drops. This is called a marine regression. When this happens, the seafloor is no longer under water. Instead, it becomes dry land.
One reason for this is ice ages. During an ice age, water turns into ice. This ice forms huge sheets on the land. Because the water is now ice, there is less in the ocean. About 18,000 years ago, the sea was much lower. It was 120 to 130 meters lower than it is today.
Moving land can also change sea levels. Large landmasses can join together into one big piece. This is called Pangaea. When land joins, ocean basins can get a bit bigger. This can cause the sea level to fall.
These changes can be hard for life. When the sea goes down, animals in shallow seas may die out. This has happened during mass extinctions. A mass extinction is when many types of life die at once. For example, the sea fell 250 meters during the Permian-Triassic event. This was the largest extinction in Earth's history.
A marine regression is a big change in our oceans. It happens when the sea level drops. When the water goes down, parts of the seafloor are no longer under the sea. These areas become dry land instead. This is the opposite of a marine transgression. A transgression is when the sea rises and covers land.
These shifts change how the Earth looks over a long time.
There are a few ways this change works. One idea is linked to how the seafloor spreads. If the spreading slows down, the ocean ridges take up less space. This can cause the sea level to drop. Another way is through ice ages. During an ice age, much of the water turns into ice. This ice forms huge sheets on the land. Since the water is trapped in ice, there is less water in the ocean.
Scientists look at history to understand these events. They see evidence of these changes in the fossil record. These shifts often happen around times of mass extinction. A mass extinction is when many different types of life die out. For example, the Permian-Triassic event happened 250 million years ago. During that time, the sea level fell by 250 meters. This was the largest extinction event in Earth's history.
Many specific dates and places help us learn. About 18,000 years ago, we were in the last ice age. At that time, the sea was 120 to 130 meters lower than today. Around 6 million years ago, a cold spell caused a regression. This also led to the Messinian salinity crisis in the Mediterranean basin. Some regressions happen without ice, like the one at the end of the Cretaceous period.
These changes affect all kinds of living things. When the sea level falls, animals in shallow seas may die out. However, mass extinctions usually affect both land and sea animals. This makes it hard to say if regression is the only cause. Some think the formation of Pangaea helped cause a regression. When all landmasses joined into one, the ocean basins grew slightly larger. This helped the sea level fall.
A marine regression is a geological process where sea levels drop. This process exposes parts of the seafloor that were once submerged. These newly exposed areas become dry land instead of ocean. This event is the opposite of a marine transgression. A transgression occurs when the sea rises and floods previously dry land.
These shifts in water levels change the shape of our continents and oceans.
Scientists have different ideas about why these regressions happen. One hypothesis involves the movement of tectonic plates. If the rate of seafloor spreading slows down, the mid-ocean ridges change. These ridges might take up less space in the ocean basins. This reduction in space could lead to a generalized drop in sea level. Such changes in plate tectonic activity might also lead to major episodes of global volcanism. Examples of this include the Siberian Traps and the Deccan Traps.
Another common cause of marine regression is the presence of ice ages. This involves the balance between the cryosphere and the hydrosphere. The cryosphere includes all the frozen water on Earth. The hydrosphere includes all the liquid water in our oceans and lakes. During an ice age, more water is stored in massive ice sheets on land. Because this water is trapped as ice, there is less liquid water available for the oceans.
This shift causes the sea level to fall significantly.
We can see evidence of these changes throughout the fossil record. Fluctuations in sea levels are thought to be linked to several mass extinctions. A mass extinction is an event where many different species die out. One major example is the Permian-Triassic extinction event. This occurred 250 million years ago (Ma). It remains the largest extinction event in Earth's history. During this specific event, the global sea level fell by 250 meters (820 feet).
Another example of a regression linked to ice is found in the Pleistocene epoch. During the height of the last ice age, about 18,000 years ago, sea levels were much lower. The ocean was 120 to 130 meters (390 to 425 feet) lower than it is today. We also see a regression linked to a cold spell around 6 million years ago. This event was connected to an advance in glaciation. It also coincided with the start of the Messinian salinity crisis in the Mediterranean basin.
Some regressions do not seem to be caused by ice at all. For instance, a major regression happened at the end of the Cretaceous period. This regression accompanied a mass extinction event. Another theory involves the formation of the supercontinent Pangaea. As all the major landmasses joined into one large body, the ocean basins changed. This coalescence might have slightly enlarged the ocean basins. This enlargement could have helped facilitate a marine regression.
It is important to understand how these events affect life. A major regression can cause marine organisms in shallow seas to go extinct. This happens because their habitat disappears as the water retreats. However, mass extinctions usually involve both terrestrial and aquatic species. Because of this, scientists see regressions as correlates or symptoms of extinctions. They are often seen as part of a larger pattern rather than the single primary cause of all life loss.
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