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Chapter 8: Problem 15

If hydrogen and helium account for \(98 \%\) of the mass of all the atoms in the universe, why aren't the Earth and Moon composed primarily of these two gases?

Short Answer

Expert verified
Despite the predominance of hydrogen and helium in the universe, the Earth and Moon are not composed primarily of these gases due to the heat and collisions during their formation which caused these lighter elements to escape. In addition, Earth's and Moon's gravitational pull are insufficient to retain these lightweight and rapid gases. Lastly, even though these elements are most abundant in the universe, that doesn't dictate every celestial body's composition, as formation conditions, gravitational force, size, and temperature can significantly influence a celestial body's makeup.

Step by step solution

01

Understand the properties of hydrogen and helium

Hydrogen and helium are the lightest and most abundant elements in the universe. They are both gases under standard conditions on Earth. These properties will affect their presence in different celestial bodies, such as the Earth and the Moon.
02

Consider Earth's and Moon's formation

The Earth and the Moon were formed about 4.5 billion years ago from the Solar Nebula. The heat produced by the formation process and the collisions of planetesimals caused lighter elements like hydrogen and helium to escape from the gravitational pull of these forming bodies due to their low atomic masses. Therefore, they are not the primary constituents of the Earth and Moon.
03

Acknowledge Earth's and Moon's gravitational pull

The Earth's and Moon's gravitational pull are not strong enough to hold onto lightweight and rapid gases like helium and hydrogen. Over time, any helium and hydrogen present in Earth's atmosphere escape into space.
04

Reflect on conditions in the universe versus Earth and Moon

Even though hydrogen and helium are the most abundant elements in the universe, the universe is mostly empty space; it doesn't mean that all celestial bodies are composed primarily of these two gases. Celestial bodies' composition can depend on many factors, including the conditions at the time of its formation, gravitational force, size, and temperature.

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