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The History of Sea Levels: From the Cretaceous Period to Present Day Climate Change

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Sea levels in several areas are reported to be increasing due to climate change. This rise is triggered by melting glaciers and ice sheets. However, it turns out that the current sea level rise is not as high as in the past.

According to a study published in jurnal Gondwana Researchin the last 500 million years, the sea level probably reached its highest peak in the past 117 million years, namely in the Aptian period.

This era is part of the Cretaceous period (145 – 66 million years ago), which had sea levels estimated to be 200 meters higher than today.

“Over the last 540 million years, the highest sea levels were in the Cretaceous, at a time when dinosaurs still walked the earth,” Douwe van der Meer, lead author of the study and an exploration geoscientist in the oil and gas industry and a visiting researcher at the University Utrecht in the Netherlands, quoted from Live Science.

“Beyond that, it’s basically just speculation,” said Jun Korenaga, professor of earth and planetary sciences at Yale University.

Evidence of Higher Sea Levels in the Past Billion Years

Research from Korenaga shows that sea levels were higher much earlier in Earth’s history at around 4.5 billion years.

According to him, this period was when the first continents were still forming and the surface of the Earth was almost entirely an ocean of water.

In his estimate, Korenaga said that sea level rise occurred in a short time because it was influenced by melting ice, as happened when the Thwaites Glacier in Antarctica experienced a significant melting process.

This could result in the collapse of the entire West Antarctic ice sheet, which would then increase the average global sea level by around 3.4 meters.

However, over long periods, changes in continental position and seafloor expansion also had significant impacts. Scientists believe that the volume of water in the early Earth’s oceans was greater than it is today.

Over the period of time since the planet’s formation, seawater has slowly flowed into the Earth’s mantle.

It is known that the last time the sea level was above the current water level was around 120,000 years ago, namely in the last interglacial period (130,000 – 115,000 years ago). At that time, modern humans still lived side by side with Neanderthals and Denisovans.

Impact of Climate Change

By 120,000 years ago, the climate had become warmer, causing the ice in Antarctica to melt and sea levels to peak at around 6 meters above the current average.

The same thing also happens in modern times. Global average temperatures are becoming warmer due to human burning of fossil fuels. As a result of this, the amount of carbon dioxide and greenhouse gases increases and results in global warming in the atmosphere.

“Even though sea levels were at their highest when ice levels were lowest, this does not fully explain the occurrence of open seas during the Cretaceous, when 30% of today’s dry land was underwater,” said van der Meer.

He said that at that time, plate tectonics also played a role. Then, he also estimated that sea levels were at their highest when South America moved away from Africa, which was around 200 million to 100 million years ago.

The continents were pushed apart as the South Atlantic Ocean formed between them.

“The new ocean tends to be shallower than the ocean it replaces. On top of a layer of hot semi-liquid rock called magma is the earth’s crust, which is divided into large plates that slide to and fro,” he explained.

“Magma that comes to the surface can solidify into new crust. If this happens, it can push the edges of the old plates back down to make room,” he added.

The Earth Holds Twice as Much Water in the Past

Meanwhile, in a paper in the journal Philosophical Transactions of the Royal Society A, Korenaga and colleagues estimate that the Earth’s surface initially held twice as much water as it does today.

Like the oceanic plates themselves, water can move in and out of magma beneath the Earth’s crust. Korenaga’s calculations show the loss of water from the surface of the ocean over billions of years.

“If this is true, then although sea levels will continue to rise, their days of highs are likely behind us. Earth’s early oceans were the highest, because there was more water to drain,” Korenaga wrote in the paper.

Watch the video “Climate Activists Demonstrate at British Broadcasting Office, Protest Climate Denial”

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2024-04-01 22:00:00
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