The main elements of the atmosphere are helium, carbon dioxide and ammonia.
There is no definite boundary between the atmosphere and outer space.
4. The Earth’s atmosphere has constant temperature.
There are no layers in the atmosphere.
Exosphere is responsible for auroras.
Most meteors burn up in the thermosphere.
The stratosphere contains the ozone layer.
9. The troposphere contains roughly 80% of the total mass of the atmosphere.
Heterosphere is a part of ionosphere.
The atmospheric density increases as the altitude decreases.
The atmosphere has no mass at all.
V. Give brief description of atmospheric layers.
VI. Read and understand the following text:
Make up your own questions to this text.
Evolution on Earth
The history of the Earth’s atmosphere prior to one billion years ago is poorly understood and an active area of scientific research. The following discussion presents a plausible scenario.
The modern atmosphere is sometimes referred to as Earth’s “third atmosphere”, in order to distinguish the current chemical composition from two notably different previous compositions. The original atmosphere was primarily helium and hydrogen. Heat from the still-molten crust, and the sun, plus a probably enhanced solar wind, dissipated this atmosphere.
About 4.4 billion years ago, the surface had cooled enough to form a crust, still heavily populated with volcanoes which released steam, carbon dioxide, and ammonia. This led to the early “second atmosphere”, which was primarily carbon dioxide and water vapor, with some hydrogen but virtually no oxygen. This second atmosphere had approximately 100 times as much gas as the current atmosphere, but as it cooled much of the carbon dioxide was dissolved in the seas and precipitated out as carbonates. The later “second atmosphere” contained largely hydrogen and carbon dioxide. It is generally believed that the greenhouse effect, caused by high levels of carbon dioxide and methane, kept the Earth from freezing.
One of the earliest types of bacteria was the cyanobacteria. Fossil evidence indicates that bacteria shaped like these existed approximately 3.3 billion years ago and were the first oxygen-producing evolving phototropic organisms. They were responsible for the initial conversion of the earth’s atmosphere from an anoxic state to an oxic state during the period 2.7 to 2.2 billion years ago. Being the first to carry out oxygenic photosynthesis, they were able to produce oxygen while sequestering carbon dioxide in organic molecules, playing a major role in oxygenating the atmosphere.
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Photosynthesising plants later evolved and continued releasing oxygen and sequestering carbon dioxide. Over time, excess carbon became locked in fossil fuels, sedimentary rocks (notably limestone), and animal shells. As oxygen was released, it reacted with ammonia to release nitrogen; in addition, bacteria would also convert ammonia into nitrogen. But most of the hydrogen currently present in the atmosphere results from sunlight-powered photolysis of ammonia released steadily over the aeons from volcanoes.
As more plants appeared, the levels of oxygen increased significantly, while carbon dioxide levels dropped. At first the oxygen combined with various elements (such as iron), but eventually oxygen accumulated in the atmosphere, resulting in mass extinctions and further evolution. With the appearance of an ozone layer (ozone is an allotrope of oxygen) life forms were better protected from ultraviolet radiation. This oxygen-nitrogen atmosphere is the “third atmosphere”. Between 200 and 250 million years ago, up to 35% of the atmosphere was oxygen (as found in bubbles of ancient atmosphere preserved in amber).
This modern atmosphere has a composition which is enforced by oceanic blue-green algae as well as geological processes. O2 does not remain naturally free in an atmosphere but tends to be consumed (by inorganic chemical reactions, and by animals, bacteria, and even land plants at night), and CO2 tends to be produced by respiration and decomposition and oxidation of organic matter. Oxygen would vanish within a few million years by chemical reactions, and CO2 dissolves easily in water and would be gone in millennia if not replaced. Both are maintained by biological productivity and geological forces seemingly working hand-in-hand to maintain reasonably steady levels over millions of years.
Currently, greenhouse gases are increasing in the atmosphere, which is related to global warming. Many scientists believe this is caused by human activity.
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VII. What new information have you learned from this article? Have you got anything to add? Discuss it into groups.
CHAPTER IV
Oceanography
1. Learn active vocabulary:
flux – течение, поток, прилив
insolation – инсоляция (освещение солнечными лучами)
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