Examining the earth, we can make the list of the "essential factors for life" a long as we please. The American astronomer Hugh Ross has made a list of his own:

Surface Gravity;
- If stronger: atmosphere would retain too much ammonia and methane
- If weaker: planet's atmosphere would lose too much water

Distance From Parent Star;
- if farther: planet would be too cool for a stable water cycle
- if closer: planet would be too warm for a stable water cycle

Thickness of crust;
- if thicker: too much oxygen would be transferred from the atmosphere to the crust
- if thinner: volcanic and tectonic activity would be too great

Rotation period;
-If longer: diurnal temperature differences would be too great
-If shorter: atmospheric wind velocities would be too great

Gravitational interaction with moon;
- If greater: tidal effects on the oceans, atmosphere, and rotational period would be too severe
- If less: orbital obliquity changes would cause climatic instabilities

Magnetic Field;
- If stronger: electromagnetic storms would be too severe
- If weaker: inadequate protection from hard stellar radiation

Albedo (Ratio of Reflected light to total amount falling on surface);
- If greater: runaway ice age would develop
- If less: runaway greenhouse effect would develop

Oxygen to nitrogen ratio in the atmosphere;
- if larger: advanced life functions would proceed too quickly
- if smaller: advanced life functions would proceed too slowly

Carbon dioxide and water vapour levels in atmosphere;
- if greater: runaway greenhouse effect would develop
- if less: greenhouse effect would be insufficient

Ozone level in Atmosphere;
- if greater: surface temperature would be too low
- if less: surface temperatures would be too high; there would be too much uv radiation at the surface

Seismic Activity;
- if greater: too many life-forms would be destroyed
- if less: nutrients on ocean floors (from river runoff) would not be recycled to the continents through tectonic uplift.
These are just some of the "design decisions" that had to be made in order for life to exist and survive. But even these are enough to show that the earth did not come into being as a result of chance nor was it formed as a result of a lucky chain of events.