Past sea level

The sea level goes up and down.

This happens for many reasons. When big ice melts, water flows into the sea. This makes the water rise.

When ice grows, it holds water. This makes the sea level go down. The shape of the ocean floor also changes. This can change how much water fits in the sea. Long ago, some lands were under the water. Now, those lands are dry.

The sea level is a busy part of our world.

The sea level on Earth changes over long periods.

These changes happen for many reasons. One main reason is the amount of water in the oceans. When big ice sheets melt, water flows into the sea. This makes the sea level rise. When ice grows on land, it holds water. This makes the sea level fall.

The shape of the ocean floor also matters. Plate tectonics, or the moving of Earth's crust, changes the ocean basins. These are the large areas at the bottom of the sea. If the basins get deeper, they hold more water. This can make the sea level lower.

About 20,000 years ago, the sea level was very low. This was during the Last Glacial Maximum. Since then, the water has risen a lot. About 10,200 years ago, a land bridge once joined Europe and Great Britain. Later, the sea covered that land. Today, the sea level is still rising. This is partly because ice in Greenland and Antarctica is melting. Scientists study these changes to understand our world.

The level of the ocean on Earth is always changing.

These changes happen over very long periods of time. Sometimes the sea is much higher than it is today. Other times, the sea level drops much lower. Most of the time, the ocean level has been higher than it is now. Only during certain times, like the Carboniferous period, was it lower. Understanding these changes helps us learn about our planet's history.

There are two main ways the sea level moves. One way is by changing how much water is in the ocean. When big ice sheets on land melt, they release water. This extra water flows into the sea and makes the level rise. Another way is by changing the shape of the ocean floor. This happens through plate tectonics, which is the movement of the Earth's crust. If the ocean basins, or the deep areas on the floor, get deeper, they hold more water. This can make the sea level go down.

Scientists use different tools to study these old changes. Some look at fossils of marine life to see where the sea once was. Others look at the rocks left behind on land. In the 1980s, researchers like Hallam used regional observations to estimate flooded areas. Other groups, like the Exxon researchers, used seismic profiles. These are tools that help them see layers of sediment buried under the coast. By studying these layers, they can see how the water moved over millions of years.

We can see big changes in our own recent history. About 20,000 years ago, the world was in the Last Glacial Maximum. This was a time when sea levels were very low. Since then, the water has risen by about 110 meters. About 10,200 years ago, a land bridge connected mainland Europe to Great Britain. Eventually, the sea rose and covered that land. Today, the sea level is still rising. In the 20th century, the rise was about 2 to 4 centimeters.

Today, much of the rise comes from melting ice. The ice sheets in Greenland and Antarctica are losing mass. In 2006, they lost a huge amount of ice combined. This loss causes the sea level to rise every year. Scientists also look at how much water we take from the ground. Moving water from underground to the ocean also changes the level. It is a complex way the Earth works to balance its water.

Sea level refers to the height of the ocean's surface. This level is not constant. It changes due to many different factors over time.

These changes can happen over millions of years or just a few centuries. Understanding sea level is vital for studying Earth's history. It tells us how the planet's surface and climate have shifted. Most of the time, the long-term mean sea level has been higher than it is today. Only during the Carboniferous or the Permian-Triassic boundary did it stay lower.

There are two main ways that sea levels change globally. The first is a change in the volume of water. This is often caused by the growth or melting of ice caps. When ice melts on land, the water flows into the ocean. This makes the sea level rise. The second way is a change in the storage volume of ocean basins. This is caused by plate tectonics. As oceanic plates age, they become denser and sink deeper. This creates deeper basins that can hold more water, which lowers the sea level.

Scientists study these changes using different methods. Some use qualitative observations from exposed geologic sections. They look at flooded areas of continental interiors. Others use seismic profiles to study sedimentary basins. This helps them see how coastal layers were buried by the sea. In the 1980s, researchers like Hallam and groups from Exxon used these different techniques. These studies help reconstruct how sea levels fluctuated during the Phanerozoic era. During this time, sea levels changed by several hundreds of meters. The highest peaks were seen during the middle Paleozoic and the Cretaceous.

We can see very clear changes in recent history. About 20,000 years ago, Earth experienced the Last Glacial Maximum (LGM). This was a time when sea levels reached a very low minimum. Since then, the sea level has rebounded significantly. During the early Holocene, between 14,000 and 6,500 years ago, the sea rose by about 110 meters.

For a long time, the sea level was stable. However, it has risen by 0.50 meters over the last 1,500 years. About 10,200 years ago, a land bridge connected mainland Europe to Great Britain. By 8,000 years ago, the sea had drowned the marshes there.

Today, melting ice is a major driver of sea level rise. This involves the mass balance of glaciers and ice caps. Mass balance is the change in the total mass of ice on land. Each year, snow falls on Antarctica and Greenland. Some of this water returns to the ocean through melting or icebergs. In 2006, the Greenland and Antarctic ice sheets lost a combined 475 billion tonnes of ice per year. This loss caused a sea level rise of about 1.3 millimeters per year. The rate of ice loss has been accelerating. By 2010, the acceleration was over 50 gigatonnes per year squared. This acceleration is three times larger than the loss from mountain glaciers.

Other factors also influence the water level. Human activities have changed how water is stored on land. Since 1930, people have impounded water in reservoirs. This has actually masked some sea level rise. However, humans also extract a lot of groundwater. Between 1900 and 2008, about 4,500 cubic kilometers of groundwater were taken. This is equivalent to a sea level rise of more than 6% of the total reported rise. The rate of groundwater depletion has increased since 1950. This adds even more water to the oceans.

Local changes can also happen due to the movement of the Earth's crust. This is known as dynamic topography or subsidence. The crust can move up or down. This changes the sea level relative to the land. Additionally, the temperature of seawater affects its density. Warmer water takes up more space, which can influence the level. All these factors work together to create the complex sea level patterns we see today. Scientists continue to use models and observations to predict future changes. They want to understand how much the ice sheets will contribute to the oceans by the year 2100.