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Chapter 19: Problem 7

Explain why the Earth is expected to become inhospitable to life long before the Sun becomes a red giant.

Short Answer

Expert verified
Before it becomes a red giant, the Sun will get much brighter, gradually elevating the Earth's temperature. This will speed up weathering processes, reducing CO\(_{2}\) levels necessary for photosynthesis. Also, as average global temperatures rise to about 47 \(^{\circ}C\), significant evaporation of the Earth's oceans will increase the amount of water vapor in the atmosphere, further raising temperatures. This climatic and environmental change will make Earth inhospitable for life, which would likely happen even before the Sun enters its red giant phase.

Step by step solution

01

Understanding the Changes in the Sun's Life Cycle

The Sun, like any other star, goes through a life cycle. Currently, it's in the main sequence stage, steadily burning hydrogen into helium in its core. However, billions of years from now, it will exhaust the hydrogen supply in its core and start to collapse under its own gravity. This will increase the pressure and temperature of the core, inciting it to burn helium and eventually turn into a red giant. But even before it turns into a red giant, it will become increasingly brighter, causing temperatures on Earth to rise.
02

Climatic Impact on Earth

As the Sun burns more brightly, the temperature on Earth will increase significantly. This rise in temperature will accelerate the rate of weathering of silicate rocks, which acts as a sink for carbon dioxide (CO\(_{2}\)). Increased weathering will lead to a decrease in the amount of CO\(_{2}\) in the atmosphere, a green-house gas that's critical for supporting life.
03

Depletion of CO2 and Impact on Photosynthesis

The reduced levels of atmospheric CO2 will make it difficult for photosynthetic organisms, since CO2 is a necessary reactant in photosynthesis. Consequently, this will deprive organisms higher in the food chain of their food source. Moreover, without photosynthesis, production of oxygen will decrease, further making Earth inhospitable for life.
04

Elevated Temperatures and Water Vapor

Continued increase in solar brightness will lead to soaring temperatures on Earth. When average temperatures reach about 47 \(^{\circ}C\) (116 \(^{\circ}F\)), the oceans would begin to evaporate substantially, increasing the amount of water vapor in the atmosphere. Water vapor is a potent greenhouse gas, and this increase will further raise global temperatures to levels intolerable for life.

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Most popular questions from this chapter

As a red giant, the Sun's luminosity will be about 2000 times greater than it is now, so the amount of solar energy falling on the Earth will increase to 2000 times its present-day value. Hence, to maintain thermal equilibrium, each square meter of the Earth's surface will have to radiate 2000 times as much energy into space as it does now. Use the Stefan-Boltzmann law to determine what the Earth's surface temperature will be under these conditions. (Hint: The present-day Earth has an average surface temperature of \(14^{\circ} \mathrm{C}\).)

Why does a star's luminosity decrease after helium fusion begins in its core?

What does it mean when an astronomer says that a star "moves" from one place to another on an H-R diagram?

Suppose you find a binary star system in which the more massive star is a red giant and the less massive star is a mainsequence star. Would you expect that mass transfer between the stars has played an important role in the evolution of these stars? Explain your reasoning.

The stars that make up the binary system W Ursae Majoris (see Figure 19-21c) have particularly strong magnetic fields. Explain how astronomers could have discovered this. (Hint: See Section 16-9.)
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