The age of mankind is negligible compared to the age of the Earth. It is difficult for us to understand the speed at which geological processes of our planet take place. It took millions of years for the oceans to form on Earth. Even in order to accumulate a bath, it takes time, so imagine how long it has passed to fill the huge basins that occupy two- thirds of the surface of the planet with water. Scientists believe that the level of the world's oceans was rising by only 1 millimeter per year. Of course, this process did not proceed evenly. At the same time, various geological processes took place, tectonic plates were raised and lowered, continents and islands went underwater, new ones were formed. Forests grew and died, living organisms developed and the climate changed. From the point of view of human life, it was all terribly slow. If you had come to Earth about 2.5 billion years ago when the world's oceans were being filled, you could have lived your whole life from birth to death without noticing what was happening.
Nevertheless, the "world floods" have occurred, and repeatedly. Geologists study rocks similar to puffed cake, where layers of marine sediments alternate with layers of purely "land". The modern coastline was formed approximately 6-10 thousand years ago. And 20 thousand years ago this line was 100 meters lower than the current one. There were forests, swamps, and tundra at the bottom of the North Sea, and the mouths of large years were located, and also, apparently, people lived there. This was not only the case in Europe. Scientists found on the Atlantic shelf of the United States at a depth of one hundred meters of deposits of peat, bones, and teeth of mammoths, ancient human settlements. And then the ice age ended, the melting of glaciers began, the level of the ocean began to rise steadily by almost 1 cm per year. So it proceeded some millennia while approximately 4 millennia B.C. there has not come a relative constancy. This does not mean that the ocean level remains at the same level. It continues to fluctuate. From 200 B.C. to 1000 A.D., the level remained relatively stable. Then began a warm period, called the Medieval climatic anomaly, and until the 15th century, the ocean level increased at a rate of about 0.5 mm per year. Then again came the period of cooling - the Small Ice Age - and relative constancy. Since the 19th century, the active rise in sea level to 2 mm per year has begun again. This is associated with another warming.
Strange as it may seem, it is much easier for scientists to measure the prehistoric pore indicators than for the last couple of thousand years. Ocean level fluctuations from 1 to 4 meters are difficult to fix, as they are superimposed on the movements of tectonic layers and water level fluctuations associated with tide, waves, and surges. What happened in the recent past is almost impossible to measure. In terms of sea level, surf strength, rock density, and other conditions have to be taken into account. And judging by the deposits (wood, peat, shellfish leaves, corals), it should be taken into account that during storms waves can throw debris up to a height of 8 meters in open areas of the ocean coast.
Mollusks can also live at different depths, and scientists use their shells to determine the age of sediments. Such a curious case is also known. In Australi, geologists have discovered a terrace at an altitude of 5-7 meters. There was a significant amount of shell remains on it, on which the age of the terrace dated back to about 5 thousand years. However, in the process of archeologists' work, it was found out that on this terrace there was a parking lot of ancient people, and fragments of shells - food garbage. And the terrace is actually much older and was formed in one of the interglacial periods about 40 thousand years ago.
The study of fluctuations in the level of the world ocean is now given great importance. This is interesting not only from the scientific point of view but also from the practical point of view. If you look at the map of the Earth, you can see how much territory is below sea level. Many coastal areas are at risk. For example, a quarter of the Netherlands would have gone underwater if it hadn't been for the powerful dams. However, it is not uncommon for storms to overflow the water to the shore and it overflows the dams, flooding vast areas. Amsterdam could be submerged in the next 150 years if the sea level rises by 1-2 meters.
Everyone knows that Venice, which is constantly sinking, can actually drown if the water level rises by another meter. Also, St. Petersburg is in danger, where in recent years there have been increasing floods. Despite the protective structures and tidal protection system of the Barrier Thames, London is also notimmune from flooding. Hamburg is located a hundred kilometers from the sea, but the position at the mouth of the Elbe makes it possible to go under the water when the ocean level rises by 2 and a half meters. In China, the system of flood protection is rather weak, so the rise of water even one and a half meters can threaten many millions of residents of Shanghai, Hong Kong, Guangzhou, and Shenzhen. North America is no better off. New Orleans already suffers quite often from storms and floods. Hurricane Katrina has destroyed almost half of the city, and this may happen again. New York is no less dangerous. During storms, the coastal part of the city gets into the flood zone, and in order for it to be completely flooded, the water must rise by 3 meters. With this sea-level rise, San Francisco and Los Angeles are also threatened by flooding.
And these are only big cities, but the entire coastal area will suffer. Namely, this zone, for example, is inhabited by 50% of the population of the USA, more than half of the population of Japan, 75% of the population of Norway and Portugal, and more than half of the total population of the planet. That is why itis so important for scientists to study the detailed picture of fluctuations in the level of the world ocean to understand the current situation and be able to predict changes in the future.