At the beginning of the earth's formation, it was still in a quasi-fluid state with large volume and low density, and there was no solid watch case. With the continuous volatilization and loss of lighter substances, the earth's volume is gradually reduced, the density is gradually increased, the interior of the earth is gradually heated, and the earth's materials are constantly differentiated and differentiated, resulting in the gradual formation of the earth's primitive layer circle. This evolution process lacks obvious geological records and is called pre-geological period or astronomical evolution period (Gai Baomin, 199 1). During the whole geological evolution period, which began about 3.8 billion years ago, the differentiation of the earth's stratosphere continued, which promoted the evolution from the lower primitive stratosphere to the upper modern stratosphere. The biological evolution developed from the low monotony to the high diversity, and the geological structure and deposit types developed from simplicity to complexity, with obvious directionality, stages and periodicity of geological evolution.
After 100 years of hard exploration, people have a deeper understanding of the evolution history and geological age of the earth, and established geological age representatives according to stratigraphic paleontological characteristics and isotopic age data (table 1- 1, figure 1- 1).
Figure 1- 1 geological chronology
Table 1- 1 geological year representative
(A) Archaean geological evolution characteristics
Archean is the oldest geological history period, with an upper time limit of about 2.5 billion years ago and a time span of 2 billion years, accounting for 44.4% of the total geological history. Lu Songnian et al. (1996) suggested that Archean should be divided into Archean, Archean, Middle Archean and Neo-Archean with 3.8 billion years, 3.3 billion years and 2.9 billion years as time boundaries, according to the division scheme of Archean by the international Precambrian Stratigraphic Branch, combined with the geological data and isotopic age data of Archean in China.
Major geological events such as the formation of primitive crust, the formation of continental nucleus and the appearance of primitive life occurred in Archean. The primitive crust was formed in Archaean, which has the nature of oceanic crust and may be equivalent to marine tholeiite. Primitive hydrosphere and sedimentary circle began to appear about 4 billion years ago. Because the primitive crust is thin and fragile, volcanism is frequent and intense, which mainly forms basic to intermediate volcanic rocks and volcanic sedimentary rocks, and later becomes greenstone, which constitutes the core of the primitive continent (primitive continental crust). About 3.5 billion years ago, "granite" circles (silicon-aluminum layers) began to appear, mainly sodium granite. The alternating arrangement of these granite belts and greenstone belts is one of the common characteristics of Archean. Most people think that the greenstone belt is a trough-shaped depression formed on the partially consolidated ancient silicon-aluminum crust. The volcanic lava and sedimentary rocks filled in it came from the upper mantle and the surrounding uplift area respectively, and the development and evolution of greenstone belt led to the formation of continental core. Primitive life in the form of bacteria may have started in a small water body with high temperature about 3.6 billion years ago, which was closely related to volcanic activity at that time. As a large fossil, the earliest cell-free organism is stromatolite-forming cyanobacteria, which is found in limestone of South African Blavy Group, with an isotopic age of about 365,438+billion years. The continental core is mainly formed in Neoarchean, and its structural composition includes greenstone belt and intervening granite belt, and the overlying sediments on it are Paleoproterozoic or newer strata. By the end of Neoarchean, two large-scale primitive landmasses may have formed.
Due to the strong transformation and destruction of geological processes in the later period, the number of Archean deposits is small. Although the Archean time span accounts for more than two-fifths of the geological history, the known Archean deposits only account for 3% ~ 5% of the global total deposits, mainly iron, gold, nickel, copper and other deposits related to greenstone belts.
(2) Geological evolution characteristics of Proterozoic.
Proterzoic is the second geological historical period, with a time interval of 2.5 billion to 600 million years ago and a time span of 65.438+0.9 billion years, accounting for 42.2% of the total geological history. Taking 654.38+08 billion years and 654.38+00 billion years as time boundaries, Proterozoic is divided into Proterozoic, Mesoproterozoic and Neoproterozoic.
Proterozoic is an important historical period for the evolution of the earth, with major geological events such as the formation of in-situ platform and continental platform, the multiple leaps of sedimentary media and biological evolution, and the emergence of global ice age. In the Paleoproterozoic, due to the small scale of the continental core, it was impossible to form completely separated sediments, and the nature of the atmosphere and water gradually evolved from the reduced state of hypoxia to the weakly oxidized state of oxygen. The emergence of eukaryotes has achieved the first leap in the history of biological evolution. Filamentous bacteria are isolated from black shale of Transwa Group in South Africa and belong to prokaryotic cells. The isotopic age of this group of black shales is about 2.3 billion years. The most abundant microfossil flora and multi-type stromatolites were discovered for the first time in the shale of the Ganfulin Formation in Canada, among which five kinds of green algae belong to eukaryotes, and the isotopic age of this shale is between 2 billion and 65.438+0.95 billion years. In Mesoproterozoic, the scale of continental core was further expanded, the sediment sorting was relatively complete, the oxygen content in the atmosphere and water was increasing, and the overlying sediments such as sandstone and clay shale were widely developed, forming a relatively developed and common active zone in and around the original platform and block. Typical caprock deposits and relatively stable platform areas (continental platforms) were formed in Neoproterozoic, mainly in the Sinian system in the late Neoproterozoic, and the nature of the atmosphere and water bodies also evolved from oxygen-containing state to oxygen-rich state. The appearance of advanced algae is the second leap in biological evolution. Red algae and large unicellular algae proliferated in large numbers about 65.438+0 billion to 900 million years ago, and brown algae represented by Phaeophyta may have appeared about 65.438+0.2 billion years ago. The "Ediacara" fauna, which was first discovered in Australia and consisted of naked imprinted fossils such as jellyfish and worms, suddenly appeared in large numbers about 700 million years ago, marking the third leap in biological evolution. Glacier deposits in Sinian spread all over the continents. The moraine layers in 740-700 million years were widely distributed, and the wet and cold climate dominated, which constituted the global Great Ice Age. After the main glacial period, most areas turned to dry heat, and dolomite containing gypsum salt appeared in South Asia and southern Australia, representing dry heat climate.
The time span of Proterozoic also accounts for more than two-fifths of the geological history, and the known Proterozoic deposits account for 15% ~ 20% of the global total deposits. Compared with Archean, Proterozoic deposits not only increased significantly in quantity, but also increased significantly in type. The main deposit types are BIF type iron ore, unconformity type uranium ore, conglomerate type gold-uranium ore, sandstone-shale type copper ore, black shale type gold ore, sedimentary type manganese ore, sedimentary type phosphate ore, SEDEX type lead-zinc-silver deposit, copper-nickel sulfide deposit, magmatic (layered complex) chromium ore and so on.
(3) Phanerozoic geological evolution characteristics
Phanerozoic refers to the geological historical period since 600 million years ago, which spans about 600 million years, accounting for 13.4% of the total geological history. Taking 250Ma and 65Ma as time limits, Phanerozoic can be divided into Paleozoic, Mesozoic and Cenozoic.
Phanerozoic is the most important geological historical period of the earth's development and evolution, and a series of major geological events occur frequently, resulting in profound changes in the earth's appearance and crustal structure. The coexistence and opposition between the relatively stable platform area and the active geosyncline area, as well as the further complication in the future, the interaction, aggregation and dispersion between the continental plate and the ocean plate, and the continental crust proliferation are the common characteristics of the Phanerozoic major geological events. At the beginning of Paleozoic, the basic pattern of platform area and geosyncline area inherited Sinian to a great extent. During the whole Paleozoic, there were usually several discontinuities in the platform area, but there were many structural changes in different areas of the active area, which made the distribution of land and sea and the structural pattern change quite significantly. Biodiagenesis in early Paleozoic is more common than that in Precambrian, and purple-red argillaceous deposits representing dry-hot climate and calcareous argillaceous deposits containing gypsum and pseudocrystals are very common. At the same time, the combustible stone coal seam formed by algae was discovered in the early Cambrian, and the real inferior coal was formed in the middle and late Silurian, which are all signs of humid and warm climate conditions. In the Late Paleozoic, large coal-bearing deposits, large reefs and shell beaches, as well as large semi-isolated salinized continental surface sea basins were formed. At the end of the Late Paleozoic, the geosynclines between the ancient platforms in the northern hemisphere were all transformed into folded mountain systems, forming a unified Lauya continent, close to Gondwana continent, and finally forming a huge Pangea. Mesozoic and Cenozoic continental sedimentary types are widely distributed, with humid and arid climatic zones appearing alternately and the crust changing strongly. Pangaea Pangaea gradually disintegrated from the end of Triassic, especially in Cretaceous, and Gondwana was the most obvious.
Phanerozoic is characterized by the unprecedented reproduction and wide distribution of various higher organisms. Marine invertebrates dominated in the early Paleozoic, and semi-terrestrial gymnosperms appeared in the middle and late Cambrian, but they were preserved as rich fossils in Silurian. The late Paleozoic completed the large-scale landing of animals and plants and the occupation of various ecological environments in the mainland. At the same time, marine invertebrates and algae are still flourishing. The remarkable characteristics of Mesozoic biological evolution are that huge reptilian dinosaurs not only occupied all continents in the world, but also returned to the ocean, and some even developed into the sky and led to the appearance of birds; Terrestrial and freshwater creatures have also developed unprecedentedly. The most important marine invertebrates are arrow stone, ammonite, foraminifera and Liusheshan. The evolution of Cenozoic organisms is characterized by the great development of mammals and angiosperms.
Phanerozoic is also the peak of mineralization. Although its time span is less than one seventh of the geological history, the number of Phanerozoic deposits accounts for more than 75% of the world's total deposits, and the metallogenic intensity has gradually increased from Paleozoic to Mesozoic and Cenozoic. There are many kinds of minerals and deposits formed in Phanerozoic, magmatic deposits and sedimentary deposits occupy an important position, and superimposed deposits are very common. The main deposit types are volcanic Pb-Zn-Cu deposit and gold-silver deposit, volcanic fluorite and pyrophyllite deposit, kimberlite diamond deposit, magmatic hydrothermal (chronological) tungsten-tin deposit and gold-silver deposit, skarn tungsten-tin deposit and copper-iron deposit, porphyry copper-molybdenum deposit, magmatic (ophiolite) chromium deposit, sedimentary oil-gas field and coal field, sedimentary manganese deposit and phosphate deposit, sedimentary bauxite deposit and steam deposit. Hydrothermal mercury antimony deposits, MVT and Sedex lead zinc silver deposits, laterite nickel deposits and bauxite deposits, placer gold deposits, placer tin deposits, diamond placer deposits, etc.