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§ 19. Geologic time (textbook)

§ 19. Geologic time


1. Remember, studying geology.

2. What made crust?


Age of the Earth. Scientists found that the age of our planet is about 4.6 billion years. The length of time during which there was development of the Earth, called Geology time. Development of the planet associated with such major events as crust formation and development of living organisms.

For billion years of Earth's crust has been subjected to lasting change. She broke in huge chunks, prohynalasya cavity, curved folds of mountains, forming deep cracks. Incandescent lava flows rose from the depths to the surface. Then millions of years it cover the sedimentary rocks. Billions of years ago in reservoirs having first organisms - bacteria and algae. For hundreds of million years of them have developed plants and animals that inhabited the dry and Sea. Over 150 million years ago the Earth had existed largest for all its history animals - dinosaurs. And only about 2 million years ago were the ancestors of humans.

As But on such ancient events were able to find people? Indeed, when this occurred, their on Earth was not yet. It turns out that the events of the planet reflected in rocks. Exploring the rocks, you can determine when they were formed and natural conditions that existed millions of years ago. Because rock is called "Stone chronicle" of the Earth.

Reading Stone chronicles the Earth. That decipher the "evidence" of rocks, exploring the fossils and their occurrence remains of plants and animals contained in them.

In crust sedimentary rocks deposited strata (Layers). In placing the layers there is a sequence: those that underlay - older, that were formed before the top. So, for Horizontal deposits of rocks can set their relative age. For example, if on a steep river bank see below limestone and above them - clay, sand covered above, it is evident that older limestone by clay and sand with clay older.


Fig. Concordance strata (layers)


Set age of rocks and can palaeontological method. It is to determine the age of rocks by the remnants of various organisms living in the past. Their remains are in the majority of sedimentary rocks. When organisms die off, the soft parts of their bodies are destroyed without a trace. However, the solid parts (Shell, shell, bone), are buried in sediment accumulation over time kam'yaniyut and well maintained. Thus, in continental sediments are the remains dinosaurs, birds and plants. In marine sediments many remnants of molluscs. We know that first appeared on Earth simplest organisms. In billions years they have changed and evolved. Thus, the remains of primitive plants and animals occur in the oldest layers of sedimentary rocks, and the most developed - in most recent sediments. There are other methods of determining the age of rocks (in years).

By age of the oldest rocks found and age of the earth. The oldest rocks, which are over 4 billion years old, found in SiberiaOn Kola peninsula South Africa, в Australia. In Ukraine common rocks of different ages. The oldest is granite, quartzite, Labradorites age 2.6 billion years.

Geochronological table. Using different methods study rocks, scientists have made a special scale. It shows the length of time, which divide geological time. Each time interval corresponds to a certain stage crust formation and development of living organisms. This scale is called geochronological table (Geochronology - from the Greek:  geo - Land, chrono - Time and ogy- Knowledge). Thus, geochronological table- A scale that reflects the sequence of basic stages of geological history Earth and the development of life on it.

By geochronological table history of the Earth divided into geological era. secrete 5 er: Archean (From the Greek - the era of ancient life), Proterozoic(Initial era of life), Paleozoic (Era of ancient life), Mesozoic(Average age of life) and Cainozoic (New era of life). Era in its turn divided into periods. For example, primary covers 6 periods: Cambrian, ordovytskyy, Silurian, Devon, Coal, Permian. Unlike the historical time that miryayut ages, geological time measured significantly longer lengths - milyonolittyamy. Duration of periods varies - from 20 to 100 million years. Only the last period of the last era - quaternary - Takes only 1.8 million years. This points to its incompleteness.

So geochronological scale gave the order to the sequence of rocks comparison and differentiation of geological phenomena and processes.


Fig. Geochronological table

Question and objectives

1. What is the age of the earth?

2. Why rocks are called witnesses of history our planet?

3. What ways can determine the age of rock rocks?

4. What does geochronological table?

5. What era in the history of Earth is the oldest, which is - the latest?