Why has water stayed liquid on Earth?

A bit of a mystery here.

Life began on Earth about 3.5 to 4 billion years ago. One prerequisite for this is that water has to be liquid. Yet the sun back then emitted 30% less heat than it does today. If the Earth had the current atmosphere of oxygen and nitrogen, all the water would be solid ice.

Obviously, before photosynthetic life, there was little or no oxygen and the atmosphere was very different. It, no doubt, contained a lot more greenhouse gases. Yet current calculations based on the purported ancient atmosphere still shows that the world would have been too cold for liquid water.

Anyone think of an answer?

haven't you herd of ice age?there was a time when earth was completely masked with ice.slowly and gently over hundreds or thousands of years it get liquified into water.

Becouse of the cycle it does.
Water( seawater) get vaporised, get's in the air, in the clouds, start to rain, get's back to the sea.
Thats how it goes.

Although the question is far from being completely answered, most theories about the origin of life on earth think it started on the ocean floor, with heat coming from hot emmissions from underneath the earth's crust. The water would have been liquid there even if the surface was frozen.

Yeah I totally agree. It had to be the ice age that caused the water to come back to earth and that water has stayed liquid on earth because life is just like that. IMO

It may taken long period to melt ice and water cycle started ..Then only life originated..Sometimes science and its findings make me wonder..