Glaciation

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The geological period when the earth was covered with large-scale glaciers

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During the ice age, the earth's surface was covered with large scale glacier Of Geological period , also known as Glacial period 。 The only relative between the two ice ages Warm period , called Interglacial period 。 earth There have been many ice ages in history, the most recent being Quaternary glaciation 。

It is a "ice age" (its time span is tens of millions of years or even 200 or 300 million years), a period of continuous global low temperature, and the continental ice sheet extended to the equator significantly. In the academic circles of mainland China, the Ice Age is also called the "Great Ice Age". The period between the adjacent ice ages when the earth's climate is relatively warm is called the "interglacial age". Four major ice ages in the earth's history: Karoo Ice Age, Antisahara Ice Age, Warangir Ice Age, Huron Ice Age; The alternating periods of cold and warm in the ice age are called ice segments (or sub ice ages, ice stages) and interglacial segments (or interglacial stages). The time scale is tens of thousands of years.

earth In the history of more than 4 billion years, there have been many times of significant cooling and ice ages. Especially in Precambrian Late stage Carboniferous to permian And the Cenozoic ice age time Long Geological events , usually called the Great Ice Age. The time scale of the Great Ice Age is at least millions of years. During the Great Ice Age climate The alternation of cold and warm and the expansion of ice sheet scale or shrink back The period of expansion and retreat is called glacial period and interglacial period.

Chinese name: Glaciation
Foreign name: Ice Age / Glacial period

Also called: Glacial period
Meaning: earth Large scale coverage glacier Of Geological period

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Concept description

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Cold Ice Age

With strong Glaciation The geological and historical period. also called Glaciation 。 Ice age can be divided into broad sense and narrow sense. The broad sense ice age is also called the Great Ice Age, and the narrow sense ice age refers to the ice age lower than the Great Ice Age. The Great Ice Age means earth The upper climate is cold, the polar ice sheet is thickened and widely distributed, and the middle and low latitudes are sometimes strong glacier Functional Geological period 。 During the Great Ice Age, the colder climate is called the Ice Age, and the warmer climate is called the Ice Age Interglacial period 。 Big Ice Age, Glacial Age and Interglacial Age are geological time units divided according to climate. The duration of the Great Ice Age is equivalent to or greater than the epoch of the geological age unit, and the time interval between the two Great Ice Periods can be several hundred million. According to statistical data, some people believe that the appearance of the Great Ice Age has a period of 150 million years. The duration of glacial and interglacial periods is equivalent to Geologic Age Period of the unit.

In the billions of years of geological history, there have been at least three big ice ages in the world Precambrian Late Great Ice Age Carboniferous -The Permian Great Ice Age and the quaternary period Big Ice Age. The remaining Moraine It is the main object of glacier research. Quaternary glaciation The moraine layer is the most well preserved, widely distributed and thoroughly studied. In the Quaternary, according to the change of glacier coverage, it can be divided into several glacial periods and interglacial periods. The ice cover area accounts for about 30% and 10% of the land surface area respectively. However, there are great differences in the development of glaciers during the glacial period in different continents, such as Europe Continental ice sheet It once reached 48 ° north latitude, while Asia only reached 60 ° north latitude. Due to regional differences and research method The division of ice ages varies from place to place. In 1909, the study of A. Penk and E. Bruckner in Germany The Alps Quaternary glacial deposits in the area are divided into four glacial periods and three interglacial periods.^[1]

There are different opinions about the cause of the Great Ice Age, but many researchers believe that it may be related to the cycle of the solar system in the Milky Way. Some people think that when the sun moves to the near silver point, the luminosity is the smallest, so that planet Cooling and forming the Great Ice Age on the earth; Some people think that the material distribution in the Milky Way is uneven. When the sun passes through the area with high interstellar material density, it reduces the solar radiation energy and forms the Great Ice Age on the Earth.

"Glacier is the product of climate", which is a popular saying in the field of glaciology. So, what is the product of climate? The author said that "climate change is Earth system The reflection of the changes in the atmosphere. The cryosphere is a part of the earth system, so people can say that "part of the climate is the product of glaciers". Of course, the main part of the climate should be Geosphere (including crust, mantle and core) product Because the geosphere accounts for 99.9% of the total mass of the earth system. Glaciers and climate are closely related, and they are also restricted by the changes of the geosphere. People can even say that "glaciers and climate are both products of the changes of the geosphere". The change of the geosphere is also restricted by cosmic factors. After long-term research, the author puts forward the following views: cosmic magnetic field and electromagnetic field of geomagnetic fluid Coupling action , may be Surface of the earth The root cause of changes in various systems is also the root cause of glacier and climate change.^[2]

Glacial period: about 1 million years ago, the Earth entered a glacial period, and vast areas were covered with ice and snow. Many species such as Saber tooth elephant 、 Giant tapir Some species such as panda 、 metasequoia Only survive in a few areas!

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Cold Ice Age

The most important sign It is the global significant temperature cooling, and a large area of ice sheets and mountain glaciers are widely formed in the middle and high latitudes (including the polar regions) and high mountain areas. As water is transferred from the ocean to the ice sheet area, Continental ice sheet Continuously expanding and thickening, resulting in a significant decline in sea level. Therefore, the climate during the ice age was dry and cold. The existence of ice sheets and changes in land and sea situations, Climatic zone The atmospheric circulation and ocean current change accordingly, which directly affect the growth, evolution and distribution of animals and plants.

After the Quaternary Ice Age, the period about 10000 years ago is called Post glacial 。 During this period, the climate still had many low-level fluctuations of cold and warm. For example, there was a relatively obvious cold period between 4000 and 6000 years ago, which made the global glaciers once expand and advance. It is called Neoglacial 。

The last obvious small-scale glacial advance occurred from the 13th to 14th century to the early 20th century (some literatures mainly refer to the 16th to 19th century), about eighteenth century It reached its peak from the middle to the middle of the 19th century, commonly known as the Little Ice Age.

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Scholars have put forward various explanations, but so far no satisfactory answers have been obtained. To sum up, there are astronomy and geophysics Cause theory.

Astronomy genesis

Astronomical genesis mainly considers the relationship between the sun, other planets and the earth.

① The periodic variation of the sun's luminosity affects the earth's climate. When the solar luminosity is in weak change, the radiation will decrease, the earth will become cold, and even the ice age climate will appear. Mirankovich believes that the reduction of solar radiation in the summer half year is a possible factor leading to the ice age.

② The periodic change of the earth's ecliptic angle leads to the change of temperature. The ecliptic angle refers to the angle of intersection between the ecliptic and the celestial equator, and its change is mainly affected by the planetary perturbation. When the declination angle is large, the difference between winter and summer increases, and the annual average solar radiation rate is the smallest, making the low latitude area in a cold period, which is conducive to the formation of glaciers.

Geophysical genesis theory

Geophysical genesis theory has many influencing factors, including atmospheric physics and geographical geology.

① The influence of atmospheric transparency. Frequent volcanic activities make the atmosphere full of volcanic ash, with low transparency, reducing the amount of solar radiation, leading to the cooling of the earth.

② tectonic movement Impact. Tectonic movement caused land uplift and subsidence, land block displacement and apparent pole movement, changed the distribution of land and sea and circulation pattern, and could cool the earth. The feedback effect of cloud cover, evaporation and ice and snow reflection further cools the earth and promotes the coming of ice age.

③ CO in atmosphere two The shielding effect of. CO two It can prevent or reduce the loss of surface heat. If CO in the atmosphere two If the content increases to 2-3 times today, the polar temperature will rise by 8~9 ℃; If today's CO2 content in the atmosphere is reduced by 55~60%, the temperature in the mid latitudes will drop by 4~5 ℃. During the geological period, the volcanic activity and biological activity caused CO in the atmosphere two The content varies greatly when CO two If the shielding effect is reduced to a certain extent, an ice age may occur.

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Cenozoic era The previous Great Ice Age is recognizable because of its ancient age Glacial vestige Scattered and incomplete, and the research degree is poor, mostly based on the zone contained in the stratum Glacial scratch It includes moraine, flint nodules in shale and bedrock chassis with glacial scratches. The glacial relics of the Cenozoic Great Ice Age are generally well preserved, especially in the late Cenozoic Ice Age, such as those with good sedimentary continuity Deep-sea sedimentary core , loess, etc., can record the changes of global climate and environment more completely. Since the 1970s, scholars all over the world have used oxygen isotope Methods such as analysis, radioactive dating and paleomagnetism try to restore and reconstruct the global climate change and depositional environment As an important basis for the division of ice age. In addition, organisms including marine organisms, mammals, plant spore and pollen fossils stratigraphy ， Geomorphologic analysis ， Sedimentary petrology The paleosol and other methods are also often used as the basis for the study of the Late Cenozoic environment and the division of ice age.^[3]

History

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Cold Ice Age

The ice age in the earth's development history only accounts for about 10% of the whole earth's historical period, and most of the time is in the warm period. The following ice ages have been confirmed.

Neoarchean Great Ice Age

It is the earliest known ice age on the earth. It is represented by the moraine layer of the Gaoganda Formation of the Huron Group in southern Canada and the western Great Lakes region of the United States, which is 2.7~235 billion years ago. In addition, in the South Africa , Western Australia and India all have the products of this ice age. The ice age will last for about 40 million years.^[4]

Precambrian Great Ice Age

A large ice age with extensive influence about 950~615 million years ago. In addition to its remains Antarctic continent Not yet discovered, many places in the world's continents have been preserved, and most of them are separated by non glacial sedimentary rocks, indicating that the glacial age was multi-stage. It was first discovered in Scotland and Norway, and later in China, Australia, Africa Greenland And North America. with Norway The tillite in northern Finnmark is its representative. In China, it is Nantuo moraine layer with scratches at the bottom of Sinian system, mainly distributed in Middle and lower reaches of the Yangtze River Etc.

Early Paleozoic Great Ice Age

Occurred from late Ordovician to early Silurian Great Ice Age 。 About 460~440 million years ago, some people think it may continue to the late Devonian (360 million years ago). Its moraine is found in France, Spain, Canada, South America, North Africa and the Soviet Union's Newland Island. The tillite outcrop in North Africa is very good, and there are several preserved Glacial Geomorphology Such as ice dammed structure, drum hill, serpentine hill and sand wedge.

Late Paleozoic Great Ice Age

Occurred from the middle Carboniferous to permian An early ice age. At that time, the global temperature generally declined, forming a large area of ice sheets and glaciers, lasting for 80 million years, which was the most far-reaching ice age in the history of the earth. It is found in India, Australia, South America, Africa and the margin of the Antarctic continent. Australia Fast Asia The southern part and Tasmania Island are the regions with the strongest glaciation during this ice age.

Late Cenozoic glaciation

It is the latest big ice age in the history of the earth. Self renewing Tertiary The glacial and interglacial periods alternate and continue to this day. As early as Oligocene, the Antarctic ice sheet began to appear, Miocene The middle ice sheet has taken shape and is the first area to enter the ice age. The glacial environment in the early Quaternary affected the whole world, and reached its peak in the middle. Therefore, the late Cenozoic glaciation mainly refers to the Quaternary glacial period. At that time, there were two large ice sheets in the northern hemisphere, namely, the Scandinavian ice sheet and North America Lauren ice sheet 。 The southern boundary of the former reaches 50 ° north latitude, and the latter reaches around 38 ° north latitude. In addition, in some high mountain areas in middle and low latitudes Piedmont glacier Or a small ice cap. About 8000~10000 years ago, the world became warm again, a large number of glaciers and ice sheets disappeared or contracted, and the earth entered the post glacial period. However, the glaciers and ice sheets in the continents have not completely disappeared.

Quaternary glaciation

Quaternary glacial period is divided as follows:

① Division of the world. 1901-1909 Germany A. Punk And E. Bruckner successively published Alps in the Ice Age (3 volumes), according to the the danube The development of several sand gravel terraces in the upper reaches suggests that the mountain area has four glacial periods and three interglacial periods, which are named G ü nz, Mindel Rhys (Rise) and wurm (W ü rm) glaciation, Gongzi Minde, Minde Riis and Riis Yumu interglacial. Later, B. Abel and I. Schafer added the older Donau Ice Age and the older Biber Ice Age. For decades, The Alps The glacial system is widely spread and used in many parts of the world, and is compared with other parts of the world as a typical glacial model.

The Earth has experienced an ice age

In the 1920s, some scholars Nordic Scandinavia At the edge of the ice sheet Denmark The terminal moraine series in the Netherlands, northern Germany and Poland has four glacial periods and three interglacial periods, from old to new, Elster Saler (Saale), Warthe Wiesel (Weichsel) Ice Age, Crowe The interglacial period between Cromer, Holstein and Eem. The ice age series in North America is mainly determined according to the classification method of the Nordic ice age Moraine and Terminal moraine The location of is divided into: Weiss Four Glacial Periods of Kangxin, Illinois, Kanshan and Nebraska, Sangamon and Ya'an Moss And Everton. Some other regions in the world have also divided the Quaternary glacial series in this region. Later, M. Milan Covic The curve of solar radiation variation established since millions of years ago shows that at least 14~15 glacial cycles can be divided, that is, almost every glacial cycle in the Alpine glacial series contains 2~3 glacial cycles. Deep sea developed in the 1950s Core oxygen isotope Research shows that the traditional Alpine glacial system is impacted because it can not record the climate and environmental change information completely, and the related strata and landforms are easily misinterpreted. The isotope of deep sea core can be recorded quite completely, which is the most accurate the pleistocene The climate and environmental change data are almost not affected by the geographical location of the core, and its continuity and universality in the world are the only ones that can be compared and verified with the reliable data of other climate stratigraphic systems. According to the 18O records of Pacific deep-sea cores, 23 18O stages and 10 complete Glacial cycle (from Phase B to Phase K), which is divided by 11 terminal boundaries (from Ⅰ to XI). stay time series It can be compared with the Alpine glacial system.

Loess is a necessary stratum of Pleistocene widely distributed on land. It has been developed since the beginning of the Quaternary, and has been almost continuously deposited until today. Due to the preservation of complete loess paleosol sedimentary sequence Biofossil And climate information, which is the most ideal object for studying the continental Quaternary environmental changes, and can also be used to sedimentary facies contrast. Loess is mostly the sediment during the glacial period, which is mainly distributed in the periphery of the ancient ice sheet in Europe and North America. During the interglacial period when the ice sheet retreated, the climate was humid and brown earth The loess and brown soil alternate sedimentary profiles were formed, recording the climatic cycle of glacial interglacial. The loess forest brown soil sedimentary sequence in Europe can be divided into several sedimentary cycles and sub cycles, and can correspond to the Nordic glacial series. Loess is widely distributed in China, with a thickness of 410 meters. Now, the research on the Luochuan section in Shaanxi Province shows that since about 2.4 million years ago, 11 paleoclimatic groups have been recorded, which can be compared with Europe Loess deposit Cycle series comparison. Among them, the loess sequence dating back to 900000 years has a good correspondence with the 1~23 stage of marine 18O.

② The division and manifestation of China. Western China The division of ice ages in alpine areas has been recognized by people to study the Himalayas better Mount Everest Taking the northern slope of the peak area as an example, the Quaternary glacial period can be divided into: a. According to Xixia Bangma Peak Early Pleistocene Shishabangma Ice Age. b. According to the glacial water moraine deposits of the Nyenishongla uplift platform on the west side of Mount Everest, the Nyenishongla glaciation of the Middle Pleistocene was established. c. In the Rongbu River Valley Keelung Broken boulders near the temple and Rongbu Temple in the upstream Terminal moraine Long represents Late Pleistocene The early Keelung Temple stage and the later Rongbu Temple stage constitute the late Pleistocene Qomolangma Glacial Age, and some scholars have divided these two stages into two independent glacial periods.

about Eastern China The issue of Quaternary glaciation is still in dispute. In 1944, Li Siguang, taking Lushan Mountain as a model, divided the Quaternary Ice Age in eastern China from old to new: Poyang, Dagu Lushan glaciation , plus the last glacial period proposed by H. von Fishman and Meng in 1937—— Dali Ice Age The Quaternary glaciation series in eastern China was established. In this regard, some Chinese and foreign scholars have always held different opinions. In the early 1980s, Shi Yafeng They proposed that: except Taibai Mountain Changbai Mountain The main peak area and Taiwan Central Mountains and other high mountains with an altitude of more than 3500 meters exist Quaternary glacial relics Besides, mountains in the middle and lower reaches of the Yangtze River, Guilin in Guangxi, Shennongjia in Hubei Beijing Xishan , the Great Khingan Mountains in Northeast China and so on are lack of reliable paleoglacial evidence; The manifestations of eastern and western China during the Quaternary glacial period are different. The eastern region does not have the water, heat and terrain conditions to develop into mountain glaciers, but is in a cold climate period. The ancient glacial remains in eastern China confirmed by Li Siguang are not of glacial origin, such as Debris flow Accumulation mistaken for moraine; The Quaternary glaciation series in the eastern region, with the exception of the Dali glaciation, lacks evidence for other glaciations.

Five ice ages

About 2.4 billion to 2.1 billion years ago - Huron Ice Age

About 850 million to 635 million years ago - ice forming period

About 450 million to 420 million years ago - Ordovician

About 360 million to 260 million years ago - Carboniferous

About 2.58 million years ago - Quaternary Ice Age

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The global impact of the ice age is significant.

1. The existence of large ice sheets has changed surface water Distribution of. During the Late Cenozoic Great Ice Age, a large amount of water in the hydrosphere accumulated on land, which caused the global sea level to drop by about 100 meters. If all the surface ice bodies melt now, the global sea level will rise 80~90 meters, and many large cities and lowlands in the world will be submerged.

2. The thickness of the large ice sheet during the ice age was up to several kilometers, which caused the local crust to slowly decline under huge pressure. Some of them were dropped by 100-200 meters, and the basement of the Antarctic continent was dropped below sea level. With the disappearance of the Quaternary ice sheet in northern Europe, the crust is slowly rising. This crust Equilibrium motion It still continues today.

3. The ice age changed the distribution of the global climate zone, leading to the extinction of a large number of warm loving animals and plants.^[5]

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Seven Great Ice Periods

Glacial fluctuation It generally includes the advance and retreat of ice tongue (its characteristic time is 101a), glacier material balance, zero balance line height change (its characteristic time is 100a) and other contents, which are closely related to short-term climate change. In the recent 40 years, there are the most various geoscience data, which can be discussed carefully. Some climatologists believe that there were two abrupt climate changes during this period, one in the mid-1960s and one in the early 1980s. In other words, the climate within 40 years can be divided into three periods. The period from the mid-1960s to the late 1970s is hereinafter referred to as the 1970s, focusing on the glacier and climate fluctuations and their possible causes.

The 1970s was a period of low temperature in the Northern Hemisphere (high temperature in the Southern Hemisphere), and most of China was a period of low temperature and little rain, Qinghai Tibet Plateau The snow area is also smaller. However, due to the adjustment of the topographic thermal circulation, the precipitation in the high altitude area during this period increased slightly, so the proportion of advancing glaciers increased greatly. This is the same as“ Little Ice Age ”The situation is quite similar.

In the 1970s earth rotation The slow segment of is Sunspot The relatively low value period of is also the period of frequent earthquakes in the mainland of China. These characteristics are similar to the "Little Ice Age".

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