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Chapter 9: Problem 25

Summarize the history of the Earth's atmosphere. What role has biological activity played in this evolution?

Short Answer

Expert verified
The Earth's early atmosphere was replaced by gases emitted from volcanic activity. The introduction of oxygen due to photosynthesis led to the Oxygen Revolution and the formation of the ozone layer. Biological activity, such as the action of photosynthetic plants and respiring animals, played a critical role in the fluctuations observed in the levels of carbon dioxide in our present day atmosphere.

Step by step solution

01

Early Atmosphere

The Earth's first atmosphere was likely composed of helium and hydrogen. This changed as volcanic activity emitted other gases, primarily water vapor, along with lesser amounts of carbon dioxide, nitrogen, and sulfur compounds, which replaced the initial atmosphere.
02

Introduction of Free Oxygen

Around 2.5 billion years ago, the Great Oxygenation Event occurred, where certain cyanobacteria began using sunlight to synthesize sugars from carbon dioxide and water, a process known as photosynthesis. This process released a byproduct: oxygen, which began to be slowly introduced to the atmosphere.
03

Oxygen Revolution

Oxygen was initially absorbed by rocks, and then by the sea, which then reacted with iron to form iron oxide sediments. When these 'sinks' became saturated, free oxygen began to accumulate in the atmosphere, leading to the Oxygen Revolution. This event caused the extinction of many anaerobic organisms.
04

Formation of Ozone

The building levels of oxygen in the atmosphere led to the creation of the ozone layer. The oxygen molecules, upon absorbing ultraviolet radiation from the Sun, became ozone (O3). This ozone layer protects Earth's surface from harmful radiation.
05

Carbon dioxide and Modern Atmosphere

In the past 600 million years, the levels of carbon dioxide have fluctuated due to the action of photosynthesizing plants and respiring animals. The present-day atmosphere is composed of approximately 78% nitrogen, 21% oxygen, and 1% of other gases (including carbon dioxide, neon, and helium).

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Most popular questions from this chapter

Ozone and carbon dioxide and ozone each make up only a fraction of a percent of our atmosphere. Why, then, should we be concerned about small increases or decreases in the atmospheric abundance of these gases?

How does solar energy help power the motion of water in the Earth's oceans?

Why do geologists think that the Earth's magnetic field is produced in the liquid outer core rather than in the mantle?

Earth's atmospheric pressure decreases by a factor of onehalf for every \(5.5-\mathrm{km}\) increase in altitude above sea level. Construct a plot of pressure versus altitude, assuming the pressure at sea level is one atmosphere (1 atm). Discuss the characteristics of your graph. At what altitude is the atmospheric pressure equal to \(0.001\) atm?

Why do you suppose that active volcanoes, such as Mount St. Helens in Washington State, are usually located in mountain ranges that border on subduction zones?
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