The Pleistocene is generally called the "ice age", but during the Pleistocene of 2 million years, the earth was not always frozen under the ice bed. In fact, in tens of thousands or even hundreds of thousands of years, the freezing period in which glaciers in polar regions and mountainous areas expand significantly, which leads to the cooling of the earth, and the warm period in which glaciers melt, which leads to the warming of the earth, alternate. Scientists learned by analyzing pollen and other scientific and technological means that there were at least two freezing periods and two warm periods. Humans born in the renewal period, relying on their own labor, constantly adapted to the natural environment of different times and regions, and created the human history and culture that continues to this day in the harsh natural environment changes such as cold climate and warm climate, that is, the humid and rainy climate on the African continent and the cold and dry climate on the desert in vast expanse. During the ice age, that is, the Pleistocene, not only the Alps, Himalayas and Alaska were still frozen by snow and ice, but other continents were also covered with thick continental ice beds like the Antarctic region. In the heyday of the Ice Age (about 20,000 years ago), from the whole area of Western Europe, Northern Europe and Eastern Europe, including most of England and Siberia, to the northern part of China, to the American continent north of the Great Lakes in North America, and the mountainous areas and surrounding areas in various regions, an ice bed with a thickness of more than 2,000 meters was covered in a vast geographical area covering the entire land area of the northern hemisphere. A large number of ice and snow cover the mainland, and the sea water will inevitably decrease accordingly. The inevitable result of the decrease of seawater is the decline of the whole sea surface on the earth. Thus, during the interglacial period from about 6.5438+0.3 million years to 6.5438+0.2 million years ago, with the melting of glaciers, the sea surface began to rise. The interglacial period lasted from 1000 to 15000.
By the end of Paleozoic, the seabed began to uplift, and after the intense "orogeny" that occurred about 230 million to 65 million years ago, the arc-shaped skeleton of the Japanese archipelago began to form. The Cenozoic after Mesozoic is divided into Tertiary and Quaternary. Tertiary, from 65 million years ago to 20,000 years ago, was the century when higher mammals and apes appeared. From about 2 million years ago to today, it belongs to Cenozoic Quaternary according to geological age. Quaternary, about 2 million years ago to 6.5438+0 million years ago, consists of Pleistocene (Pliocene) and Holocene (alluvial) periods. Pleistocene lasted from about 20,000 years ago to 1 10,000 years ago, and Holocene lasted from 1 10,000 years ago. In the history of the earth for hundreds of millions of years, it can be called "modern" Cenozoic Quaternary, and it is also the century in which volcanoes, lakes, rivers, hills, basins, plains and other things visible to the naked eye on the surface of the earth began to appear today. Especially in the Pleistocene, the earth changed repeatedly, which had a great influence on the human beings born later. For example, on the eastern edge of the Asian continent, after drastic crustal changes, the basic framework of the arc-shaped South and North Japanese islands began to take shape, which changed several times in the Pleistocene, and one of the main reasons for this change was the rise and fall of glaciers.
At the peak, the sea level dropped by about 100 to 200 meters. In the waters around the Japanese archipelago, there is a continental shelf more than 200 meters away from the sea; For Ma Haixia, which blocks the mainland and Kyushu, the water depth is less than140m; Tsugaru Strait between Hokkaido and Honshu, with a water depth of about140m; The Zonggu Strait, which spans Japan and Russia, is 40 meters deep. The Miyako Strait connecting northern Hokkaido and Sakhalin Island is only about 40 meters deep. During the ice age, when the sea level dropped more than 100 meters, the northern and southern ends of the Japanese archipelago were intermittently connected by the continental shelf and the mainland. In other words, "Japan" at that time was not an "archipelago".
From the Pleistocene strata in various parts of Japan, through archaeology, more than 20 kinds of elephants such as mammoths and fossils of large animals such as tigers, rhinoceroses and deer have been unearthed. In today's Japanese archipelago, many mammalian fossils have also been unearthed. Those extinct animals came to Japan from the Asian continent in various times when Japan was still connected with the mainland through the continental shelf. According to the above fossil data and evidence of geological research, scientists infer that the age of the formation of the continental shelf can be traced back to about 20,000 to 30,000 years ago, 50,000 to 60,000 years ago, and the oldest can be traced back to 6,543,800 years ago. In the late ice age about 1 10,000 years ago, due to the uplift of the submarine crust and the rise of the sea surface, the Japanese archipelago was finally formed.