Becz on earth fulfils all the requirements that is needed for the living org to survive , like it has methane gas , a symbol for life, adequet proportion of gases, temp, atmosphere, etc
Life is present on the Earth only due to the following reasons:
1. Oxygen and the gases which are suitable for life are present on the Earth.
2. Earth is at an equal distance from the Sun so it has a good temperature.
3. Earth is covered with a layer of atmosphere which acts as a blanket or shield and protects the Earth from the harmful UV solar rays which come from the Sun. They are very dangerous for humans.
4. Earth also has water. Many years back Jupiter pushed asteroids from their belt. Those came on the Earth and water was in them. So many of them fell on Earth and water was formed .