The earth has layers - mainly because dust from our solar system is constantly getting caught in our gravity well - falling to the planet surface - piling on top of and covering up what is already here. Estimates vary, but the USGS says at least 1,000 million grams, or roughly 1,000 tons of material enters the atmosphere every year and makes its way to Earths surface.
The layers are like the shields (like the layers above us) but in the bottom of the earth. There are heat and lava inside the earth, and the layers are too strong so it protects us from the flowing lava. If the earth didn't have any layers, we wouldn't even be here in the first place!!!^^
If we didnt have multiple layers around our earth, all the hot lava would pour out and we wouldnt even be able to be living her!
If the Earth didn't have layers, All the lava would pour out and we would die of the incredible heat!!!