Explain why the earth without its atmosphere would be inhospitably cold.

Hint: Remember that cold is absence of heat.
A body is warm if it can produce heat on its own or some form of energy is given to it externally.
Earth does not produce energy on its own.

Complete answer:
As we have discussed above, cold is absence of heat. The Earth on its own does not produce any heat Energy, it gets the heat energy from the Sun.
The Earth either absorbs the heat energy and reflects the heat energy. Now when Earth absorbs the heat energy, its temperature increases. This energy is absorbed by all objects present on the surface and also heat is trapped in the gases present in the atmosphere.
These gases are important for us. Our atmosphere protects the Earth from the harsh rays of the sun and reduces extreme temperatures, which acts like a blanket for our planet. Meanwhile, the gases are the effective means that energy from the sun that reaches Earth gets trapped in the atmosphere. These gases are known as greenhouse gases. There are several different types of greenhouse gases: namely carbon dioxide, water vapor, methane and nitrous oxide. Without the greenhouse effect and the atmosphere, Earth's temperature would be inhospitably cold.
Additional details: Today, greenhouse gases are getting out of control. The carbon dioxide emission into the atmosphere has drastically increased, Earth's greenhouse effect is getting stronger. As a result, the planet's climate gets warmer.

Note:
Remember that the atmosphere acts like a blanket for the energy which is reflected back. Greenhouse gases are increasing, which leads to the risk of global warming. Without an atmosphere, the planet would be cold.
Our atmosphere protects the Earth from the harsh rays of the sun and reduces extreme temperatures, which acts like a blanket for our planet.