Why does Earth have a liquid water supply and Mars does not?
Mars is too cold.
The size of Mars is similar to Earth's size, and its gravitational pull is about the same force of that of Earth. Mars has a layer of frozen liquid beneath its dusty orange surface. This liquid is believed to be the same liquid as Earth's water. Mars is also believed to possibly support living microbes like those on planet Earth.
yes, Mars did look like the earth. It had liquid water on it. It does not look like earth anymore because the core of the planet cooled down and when that happened it lost its magnate field. The core cooled down faster than earth because mars is small the earth. The earth and mars will die the same way.
I would say water, depending on what you're doing. I think they did finally find ice on Mars, but if it's something older, than water may be the answer. LIQUID water. Many planets and/or moons have water, but Earth is the only known planet with liquid water. Actually, we have water naturally occurring in solid, liquid, and gas phase.
If you mean liquid water, then the Earth is the only planet. Mars has water ice in abundance but if melted, would probably not be anywhere near as plentiful as Earth. NASA calculates that if all the water ice was melted, Mars could be covered by water to a depth of 11m. So, as of 2010, no known planets have the same amount of water as Earth.
There isn't enough oxygen in the atmosphere, and the pressure is too low. There's no liquid water on the surface and no food. The temperature is too cold most of the time. Living there would require a pressure dome and a supply of all the basic items for living : oxygen, food, water, Earth plants and animals.