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Current calculations show that Earth is about 4.6 billion years old. Analysis of rock layering and their subsequent deformations allows us to determine which rocks or processes are the oldest. During the research, it is difficult to determine how many years old a given rock is, but you can tell from which rock it is older, and from which it is younger. The type of rock provides information about the conditions in which it was created. If there are remains of old plants or animals in it, or fossilsfossilsfossils, then its age is limited to the period when these organisms lived on Earth. This is how we determine the relative agerelative agerelative age of rocks. When examining the content of radioactive elements using (radiometric datingradiometric datingradiometric dating), it is possible to calculate how many years has passed since the rock was formed, i.e. determine its absolute ageabsolute ageabsolute age.

Thanks to the simultaneous application of all methods of determining the age of rocks, it was possible to create a geologic time scalegeologic time scalegeologic time scale covering the entire history of Earth. The most important events helped to distinguish the so‑called geochronological units. For determining the geological time, the most often used units are eraseraeras lasting tens and hundreds of millions of years. They are part of eonseoneons – the longest units lasting from half a billion to several billion years. Less significant but still very important geological events visible in the rocks enabled the division of an era into geological periodsgeological periodgeological periods.

Geology knows and applies much more detailed divisions of the history of Earth. After the invention of radiometric dating, it was possible to supplement the geologic time scale with the duration of individual eras, periods and their parts.

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Nagranie filmowe wyjaśniające, na czym polega datowanie izotopowe na przykładzie czasu rozpadu atomów potasu i argonu.

Nagranie filmowe wyjaśniające, na czym polega datowanie izotopowe na przykładzie czasu rozpadu atomów potasu i argonu.

Film dostępny na portalu epodreczniki.pl

Nagranie filmowe wyjaśniające, na czym polega datowanie izotopowe na przykładzie czasu rozpadu atomów potasu i argonu.

How can a bunch of old newspapers be a model of rock layers?

Relative and absolute age

Observation 1

Understanding what relative and absolute age is.

You will need

• a few or a dozen of old newspapers,

• a pencil and crayon.

Instruction

1. Arrange a pile of newspapers. At the very bottom, place the oldest one, and the newest one at the top.

2. After arranging four newspapers, put a pencil on them, leave a pencil on the next five.

3. Mark the remaining newspapers according to the recommended order. Let the model created this way help you in answering the following questions.

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Zdjęcie przedstawia stos ułożonych jedna na drugiej gazet. W jednej trzeciej wysokości stosu z gazet wystaje czerwona kredka. Z kolei w dwóch trzecich wysokości ze stosu wystaje ołówek z gumką.

Summary: When analysing the arrangement of rock layers, we can conclude which rocks are older and which ones are younger, i.e. we can determine their relative age. If we know the specific age of a rock in which the fossilized organisms remained, we can determine the absolute age of these fossils.

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Ilustracja przedstawia uproszczoną tabelę stratygraficzną. Tabela dzieli historię ziemi na eony (aeon)- phanerozoic, protezoic oraz archean. Z kolei phanerozoic dzieli się na ery: cenozoic, mesozoic i paleozoic. Cenozoic ostatecznie jest jeszcze podzielony na epoki (period) - quaternary, neogen i palaeogene. Mesozoic dzieli się na epoki - cretaceous, jura i trias. Paleozoic z kolei to epoki - perm, carboniferous, devonian, silurian, ordovician i cambrian.Eony protezoic i archean są oznaczone w tabeli jako Precamber - nie jest to ani era ani okres. Tego określenia używa się zwykle do opisania czasu od powstania Ziemi do kambru. Ostatnia kolumna zawiera datowanie bezwzględne, które wynosi kolejno: Czwartorzęd- Holocen- 11,7 tys., Plejstocen- 2,6 mld; Neogen- 23 mln, Paleogen- 66 mln, Kreda- 145 mln, Jura- 201 mln, Trias-252 mln, Perm-299 mln, Karbon- 359 mln, Dewon- 419 mln, Sylur- 443 mln, Ordowik- 485 mln, Kambr- 541 mln oraz Prekambr- 4,6 mld.

Events that shaped the geological history of Earth.

The further into the geological past, the less we know about the environment, processes and phenomena that occurred then. Thanks to many years of researches and improved methods, scientists managed to get to know the main events of the geological history of Earth.

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Ilustracja w formie spirali. W górnej części spirala przypomina skamieniały amonit. Na spirali przedstawione są epoki z historii ziemi zaczynając od czasów najnowszych. Środkiem spirali przepływa woda, w której widoczne są nieistniejące już zwierzęta. Kolejne opisane epoki to: Cenozoic Era, Mesozoic Era, Paleozoic Era, Precambrian, 1 billion years ago, 2 billion years ago.

• In the earliest unit of geological time – Archean lasting up to 2.5 billion years ago – Earth's crust, atmosphere and hydrosphere were formed. The foundations of all continents also appeared.

• In the Proterozoic, lasting from 2.5 billion to approx. 540 million years ago, the first primitive forms of life in the oceans appeared.

• In both of these eras, there were many orogenies, or mountain‑forming movements. Mountain chains, that were elevated as a result, were destroyed due to erosion processes.

• In the Palaeozoic era, lasting from about 540 million years ago to about 250 million years ago, there were two orogenies, which left traces visible to this day in the form old, highly eroded mountain chains. The end of Silurian and the beginning of Devonian were marked by the Caledonian orogenesis, thanks to which there was, among other things, the uplift of some regions of the Świętokrzyskie Mountains. In Carbon and Permian, the Hercynian orogenesis occurred, which in Poland is responsible for the geological formation of the Sudetes, but also the folding of the previously created Świętokrzyskie Mountains. In Palaeozoic, organisms evolved. Fish appeared as well as the first amphibians that came out of the oceans. They quickly developed into reptiles. Between the Palaeozoic and Mesozoic eras, over 90% of all organisms have died out due to a gigantic volcanic eruption and numerous climate changes.

• In the Mesozoic era, lasting from about 250 million years ago to 66 million years ago, the process of lithospheric plate movement intensified and the original land masses broke down. The reptiles had mastered all environments, and the first birds and mammals appeared. It is possible the impact of a huge asteroid 66 million years ago caused the destruction of 75% of all organisms, including great dinosaurs, marine reptiles, ammonites and many other species.

• The Cenozoic era, lasting 66 million years ago to this day, is dominated by the mountain‑forming movements of the Alpine orogenesis (Carpathians are formed in Poland). During this era, mammals and birds dominate. Serious and repeated climatic changes have greatly modified the image of our planet. In the youngest period of the Cenozoic, Quaternary, there are glacial and interglacial periods in succession, humans Homo sapiens appeared.

According to the present state of knowledge, a Neanderthal appeared in Europe about 350‑400 thousand years ago. Among the people living in Europe, typical Neanderthal features disappeared about 25,000 years ago, which is the basis for the hypothesis that Neanderthals become extinct.

Summary

• There are many methods for determining the relative age of rocks; one of them is to analyse the rock layering in relation to each other.

• Radiometric dating allows to determine the absolute age of rocks and fossils.

• A geologic time scale shows the history of Earth in a concise way.

• Palaeontology is based on the study of fossils, especially index fossils.

• The history of Earth is a string of repeated orogenies, lithosphere movements, climate change and the continuous development of life interrupted by short periods of mass extinction.

Keywords

geologic time scale, radiometric dating, palaeontology

Glossary