? Prokaryotes appeared 3.5 billion years ago.
? Cambrian (600 million years ago), bacteria and algae.
? In Ordovician (500 million years ago), echinoderms were diverse and invertebrates.
? In Carboniferous (350 million years ago), terrestrial spore plants (ferns) flourished, amphibians diversified, and the earliest reptiles appeared.
? Early dinosaurs and mammals appeared in Triassic (230 million years ago), gymnosperms began to dominate, and marine invertebrates were diversified.
? In Jurassic (654.38+0.8 billion years ago), reptiles were diversified, birds appeared, and gymnosperms dominated.
? Tertiary Miocene (23 million years ago), mammals, birds, quilts
Offspring and insects adapt to radiation.
? The Quaternary Holocene (2.5 million years ago) witnessed the emergence of human beings.
Compare the generation of biodiversity on the earth to one year (Mayr, 199 1).
? The birth of the earth-1.
? Life appeared-February 27th.
? Eukaryotes appear-September 4th.
? Vertebrate appearance-165438+1October 2 1.
? Mammals appear-65438+February 65438+February
? Primates appear-65438+February 26th.
? Apes appear-12.30 0 1: 00.
? Human appearance-65438+February 3 1 day 1 1: 56 minutes and 30 seconds
Scientists have found that there are some trace radioactive elements in the crustal rocks. These elements decay at their respective fixed rates, that is, they gradually become ordinary elements in the form of radiation. So according to the ratio of lead to uranium in the rock now, we can calculate the age of this rock. In a similar way, scientists have measured the oldest rock on the earth, which is about 3.8 billion years old. Considering that it will take some time for lava to cool and solidify into rocks, some people think that the earth began about 4.6 billion years ago.
Early estimation of geological time
1658, Archbishop Heuchel of Ireland thought that the earth was born in 4004 BC, which was calculated according to biblical chronology, which was unacceptable to geologists in the late18th century and19th century, because most geologists, even hydrogeologists like Werner and Buffon, thought that sedimentary rocks in the crust would take at least tens of thousands of years.
(1) sedimentation rate: As early as the 5th century BC, Herodotus had studied the Nile Delta. According to the annual rate of sediment deposition, he inferred that the delta must have a history of thousands of years. Later, especially at the end of19th century and the beginning of 20th century, people calculated the age of the earth according to the maximum thickness and sedimentation rate of sedimentary rocks. Since the formation of the earth, it is estimated that the deposited thickness has reached 33. 000- 100000 meters of sedimentary rocks, the estimated sedimentation rate varies greatly, ranging from 50-3000 meters every million years. The estimated age of the earth is 17 to15.84 million years.
(2) Salt in the ocean: Early people tried to determine the age of the earth according to the comparison between the total salt content in the ocean and the increasing salt content every year. This scheme assumes that the ocean was a fresh water body in the early stage of the earth's history. It is estimated that the total salt content in the ocean is 16× 10 12 tons. The annual salt increase is1600,000 tons (mainly from salt carried by weathering of rock and soil and river dissolution). Using this inference method, the age of the earth is about1100,000 years. However, this calculation does not take into account the large amount of salt in sedimentary rock series in many parts of the world.
(3) cooling rate:19th century, British physicist L. Kelvin determined the age of the earth as 70 million years according to the cooling rate of the earth. Kelvin assumed that the earth started with molten material thrown by the sun, and the initial temperature of the earth was the melting point of ordinary igneous rocks. The error of this calculation lies in Kelvin's assumption that there is no heat source inside the earth, because it was not known at that time that radioactive decay could release a lot of heat energy.
relative age
The relative age is determined by the sequence of sedimentary rocks, original structure, unconformity, transverse structure and crater.
(1) sequence
The new stratum is deposited on the old stratum. Therefore, if they are not disturbed by folds or faults, the relative age of strata can be determined by their positions in the sequence.
(2) Primary structure
Primary structures are formed when rocks are deposited, and some of them can be used to determine their relative ages. They include cross bedding, grain-size layers, wave marks, fossils and pillow lava. Cross bedding can be formed by wind or groundwater flow, and the angle of cross bedding can range from horizontal to 40. Erosion will flatten the top of these layers and make them truncated. However, the bottom of cross bedding is usually parallel to the bottom of each layer. In this way, cross bedding can be truncated by it. It can be used to establish the relative age of a sedimentary rock series, and the concave surface of the staggered layer generally faces the new layer (top). In the particle size layer, from the bottom to the top of the single layer, the particle size changes from coarse to fine. The granular layer is formed by intermittent submarine undercurrent, the most common of which is turbidity current. Turbid flow is a high-density water body carrying sediments. The water flows down the slope quickly, and when the water slows down, coarse-grained materials are deposited first.
(3) Non-integration
In many sedimentary rock sequences, not all the original sediments can be preserved. Rising can form an erosion surface and then be covered by new sediments. This buried erosion surface is called unconformity, which can be used to determine the relative age of strata. The main unconformities are unconformity, angle unconformity, parallel unconformity and fault unconformity. Unconformity means that sedimentary rocks are covered with older metamorphic rocks or plutonic igneous rocks. Angular unconformity separates young, slightly deformed sedimentary rocks from inclined or folded sedimentary rocks, and there are angular differences between the unconformity upper and lower layers. Parallel unconformity refers to the undulating buried erosion surface between basically parallel rock layers. If fossils prove that the ages of these two rock formations are obviously different,
(4) staggered structure
Igneous intrusive rocks (such as dikes, dikes and bedrock) are always younger than the latest strata they invaded, but older than the unconformity of the oldest strata covering them. If two intrusive rocks contact, the relative age of igneous intrusive rocks can also be determined by interpenetrating relationship. Generally speaking, young intrusive dikes pass through older intrusive rocks. If strata move along faults, the relative time of their movement can also be determined. The final displacement of the fault must occur because of the fault.
Similarly, the age of folded rock series is always later than the youngest folded rock series, but earlier than the oldest folded rock series covered on it. The age of metamorphic rock series is always later than the youngest metamorphic rock series, but earlier than the oldest undisturbed rock series covered on it.
(5) the law of biological sequence
The evolution of biology is from simple to complex, from low to high, and constantly evolves and develops. Therefore, generally speaking, the newer the stratigraphic age, the more advanced and complex the creatures it contains. On the other hand, strata in different periods contain different types of fossils and their combinations, while strata formed in the same period and geographical environment contain the same fossils or fossil combinations, no matter how far apart.
According to the appearance of biological assemblage, the approximate age of strata can be inferred. After years of research, paleontologists have chosen a series of fossils or fossil combinations as standard fossils to determine the stratigraphic age. For example, graptolites are often used as standard fossils of Ordovician and Silurian.