Why is the earth hot?

Its just hype

The very simple way to think of it.

When you are floating in space 1 ray hits you and keeps going, then another ray hits you and keeps going, then another. It's always one ray, which by itself is not much energy so you always stay cold.

When you are on the planet 1 ray hits you coming down. Then it bounces off the planet and 1 ray hits you again going back up. Then the ray bounces off the clouds and comes back down plus one more ray enters. So now you get hit with two rays. The two bounce off the planet and go back up hitting you again. Then they bounce off the clouds plus one more, so now you have three rays that hit you.

Multiply this by a lot and you have a simplified version of the greenhouse effect. The reason our planet is warm and space is cold.

Since the late 1800's, the temperature of the Earth's surface has risen, and it is predicted that this increase will continue.This phenomenon, known as global warming, is thought to result from human activities.By burning wood and fossil fuels such as coal, we have increased the amount of carbon dioxide in the atmosphere by 25 percent.At the same time the average temperature of the world's surface has increased by about 0.8 degree celcius.It seems likely that there is a connection between this temperature increase and increased levels of greenhouse gases, such as carbon dioxide..

In order to transfer energy to matter the photons of light need to interact with the electrons of the matter. The matter absorbs the photons and the electrons gain energy. That is converted into heat. The atmosphere and space is transparent to visible light. Space is normally transparent to all electromagnetic radiation so the photons don't interact with the matter in space. Heat energy gets trapped by certain molecules like water vapor and CO2 in our atmosphere. Heat that you feel from a distance is transferred by a different sort of electromagnetic radiation where the wavelength is longer than normal visible light. It is called infrared radiation. Even visible light gets absorbed by many solid materials and it warms them up also. That is why black objects get warmer more quickly. They absorb more frequencies of light.

It got very hot when it was formed. And there is left over heat and radiation decay keeping it going but it is cooling down. I suppose there is a bit of friction going on as well as the plates slip and slide etc.