How can there be life on earth?
Earth has a breathable atmosphere, Water, Energy.
What is a breathable atmosphere?
Here on Earth, we have oxygen! Humans need oxygen to live. Most planets, do not have oxygen. Therefore, we cannot live there.
What is water have to do with life?
Water is everything in life. Without it, we would not be here. Roughly, 60% of our bodies are made up with oxygen. With water, the ingredients for life as we know it, such as DNA and proteins, can swim around and interact with each other to carry out the reactions needed for life to happen.
Why do we need energy?
Energy? Isn't that what powers my home? Electricity right?
Yes, and no. Yes, Electricity is energy. But, we are not referring to that. Energy or Food, is essential for life. The human body needs food and water to survive. A human can go for more than three weeks without food (Mahatma Gandhi survived 21 days of complete starvation), but water is a different story.
Wait, does this mean I can go buy a home on Mars?
No, Mars does not have oxygen in the atmosphere, if any, it is too little for human life to thrive on. Also, in the time of the writing, there is found to be no water on Mars. There also is no "Energy" on Mars. So, you cannot thrive there without food.
Okay, all of this is good? But, where can I go to get more?
There are a lot of websites that teach you about this topic. I'll list one of them here, check it out.