Earth-sized egg

The Earth's atmosphere traps heat from the Sun through the greenhouse effect, so the Earth would be considerably cooler without the atmosphere.

We would also die due to lack of oxygen and harmful UV radiation from the Sun being exposed to us. So there's that.

When we say "the temperature of the Earth" , we actually mean the temperature of its atmosphere. What we measure at meteorlogical stations is the temperature of the atmosphere, not of the planet's core or the ground surface!. So, in a sense, asking about the temperature of the atmosphere without atmosphere is a bit contradictory!.

But imagine we gradually reduce the density of air in the planet until reaching zero , also imagine that we measured temperature at each step. Each temperature measurement would be lower than the previous one, because the temperature of a gas is directly proportional to its density. When the density of the gas is zero, then its temperature is...?... well... minimum (I don't dare to say absolute zero, because I don't know if that's true).... But yes, a dense atmosphere should be warmer than a "zero density" atmosphere...

Now what if we measured the temperature of the ground? . This is where it gets a bit confusing, because the ground will loose less heat without an atmosphere!. In real conditions (with an atmosphere) the solid ground looses heat in two ways: Radiation and Conduction. The ground radiates long wave electromagnetic "heat" towards the empty space, with or without atmosphere. But the ground can only loose heat through conduction if it's "touching"a dense body, for example the dense atmosphere, If there's no atmosphere, there is no heat loss through conduction, only through radiation.

The question is quite tricky...

The answer is found using the Stefan-Boltzmann equation.

T = [{S*(1-A)}/{4εσ}]^(1/4)

T = temperature (K)

S = average solar energy received (1,366 W/m^2)

A = planetary albedo (currently 0.3)

ε = emissivity, which is the fraction of heat emitted into space (for the earth, 0.98 without the atmosphere; effective emissivity of 0.615 with)

σ = Stefan-Boltzmann constant (5.6704 x 10^-8 W/m^2/K^4)

Solving for T assuming no atmosphere gives us

T = [{1366(1-0.3)}/{4 0.98 5.6704 x 10^-8}]^(1/4) T = 256.1 K = -17.05ºC = 1.31ºF

The Earth would have an average temperature of -17.05ºC (1.31ºF) without an atmosphere, as compared to the actual average of around 14.5ºC (58ºF).

Mars is a prime example of a planet similar to ours with (essentially) no atmosphere, whose average temperature is -55 celcius compared to around 14 on the Earth.

Ignore the sun for a second and take only what the problem gives us. The problem specifically states that the atmosphere absorbs heat from the earth. It says nothing about what it does with the heat from the sun. Given this, for the sake of the problem, one must assume that the amount of heat trapped from the sun remains the same whether we have an atmosphere or not otherwise you simply are not given enough details to solve the problem.

Once you make the assumption that the heat from the sun remains constant whether there is an atmosphere or not, you can then accept the fact that given what is stated in the problem, more heat from the earth is trapped in the presence of an atmosphere than without an atmosphere. That then means that there is more heat trapped close to the earth with an atmosphere than there would be without one.

Incoming radiations from the sun are high frequency radiations. Earth absorbs that and emits low frequency radiations.

The atmosphere has the ability to trap low frequency radiations, but it does not affect high frequency radiations. This causes green house effect. (allowing high freq. incoming radiations but trapping low freq. outgoing radiations)

If there is no atmosphere, high freq. Radiations will not be affected. But low frequency radiations will not be trapped anymore. so the temperature will be low both in day and night.

I'm not sure if my line of reasoning is correct but mine was that the atmosphere has the ability to absorb heat. Remember the days of thermodynamics lecture in physics or chemistry. Everything has a specific heat capacity, meaning everything has the ability to absorb some amount of heat before their temperature goes up. Therefore, the atmosphere can absorb more which would have been otherwise absorbed by the Earth if there was no atmosphere.

Remember also from thermodynamics that radiation is the weakest form of transferring heat out of the three ways you can do it---the others being conduction and convection, AND that air, for the most part, is a very good insulator. This and the last paragraph don't necessarily have anything to do with each other. There's no known correlation with specific heat capacity and insulation. But to go back to my point, because there is a layer of insulator between the heat source and the Earth, less heat can get through to Earth to warm it up. (This is exploited in designing thermos.)

It's an interesting problem, really, especially for the modern mind, because global warming/climate change is in the public consciousness. It's easy to fall into the trap that it will get cooler because the atmosphere traps heat in, BUT one has to remember, the reason why the greenhouse effect is becoming prominent on Earth, and why it exists in Venus, is not because of the atmosphere's existence but of the atmosphere's chemical composition.

I'm not sure about physics behind it. but the presence of atmosphere does keep earth warmer, I think mainly due to the fact that it contains gases that traps heat in it kind of cooking earth from outside. without it the part facing sun will be hotter as its heat directly reaches the earth surface ....the other part without sun would be very cold because earth is unable to keep heat ......so it would be like a planet of half extreme cold and another half of extreme heat

I don't like the available answers. The atmosphere moderates wide swings of temperature over time. The surface of the moon is extremely hot facing and the dark side is extremely cold.

This layer protect us from sun"s direct heat . So if it is absent the earth will be warmer

atmosphere is a type of layer through which sun rays can come but can't go....

Global Warming...

IF THERE WOULD HAVE BEEN NO ATMOSPHERE, THEN EARTH WOULD HAVE RADIATED HEAT INSTANTLY AFTER ABSORPTION OF HEAT. AND ALSO THER WAS NOTHING ELSE TO RERADIATE BACK THE HEAT.HENCE THE TEMPERATURE WOULD BE COOLER. THUS WE CAN SAY THAT THE ATMOSPHERE KEEPS THE EARTH WARMER.

The earth is getting warmer because of the greenhouse effect in the atmosphere.

The sun sends UV rays to the Earth to warm it, but the Earth cools by releasing Infrared Radiation rays into the atmosphere. This radiation is caught by the atmosphere and reflected back to the Earth, warming it more than if there was no layer. This is the Greenhouse Effect. It is an essential part of warming the Earth and avoiding a 2nd Ice Age, but there is a balance to how much gas can outputted before it becomes a problem. Too much gas is in the atmosphere and it is causing adversities in climate and weather patterns. This is the Climate Change and Global Warming crises. Furthermore, gases are caused by more than just pollution, CO2 is also a natural byproduct of combustion, including volcanic eruptions and forest fires that also contribute to the Greenhouse Effect.

The Greenhouse Effect is an essential part of life, but there has to be a balance to how much gas is ejected into the atmosphere

The phenomenon is most popularly known as Green house effect. Various green house gases absorbs the heat reflected from the earth surface and allows lesser part of it to escape out of the atmosphere keeping the earth temprature warmer.