This is a schematic showing where material forms.
Click on image for full size
Image from: After Moons and Planets
The effect of Temperatures on the condensation of certain materials
This diagram shows that when the nebula is very hot, the rocky materials such as Calcium, Magnesium, Iron, Nickel, and Lead, that the terrestrial planets are made of, will begin to form close to the sun, but that the ice of which Uranus is made will not condense unless the temperature is very low. Thus the Earth could never have as much ice as Uranus has.
In the picture, the proto-sun is shown at the top, and the temperature in the nebula is shown to decrease with distance away from the proto-sun, towards the bottom of the drawing. The temperature at which ice begins to form is the freezing temperature, near 250 K on the diagram. The temperature at which rocky material can begin to form is much higher.
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