Not too hot, not too cold

The idea

Liquid water is essential for life, and Earth is at just the right distance from the Sun for water to stay liquid; the range of distances from a star over which water remains liquid is the habitable or Goldilocks zone.

Water and life

Liquid water is essential for life. Planets are at different distances from the Sun.

What distance from the Sun is best for liquid water?

• Neither too close nor too far
• As close as possible
• As far as possible

Three distances

Open each tab.

The Goldilocks zone

Earth is at just the right distance, where the temperature allows water to exist in liquid form. The range of distances over which water remains liquid is called the habitable zone, or the Goldilocks zone. Liquid water is essential for life to evolve, as far as we know.

Earth is at just the right distance from the Sun for liquid water. The range of distances over which water stays liquid is the habitable zone (Goldilocks zone).

Notes

The habitable (Goldilocks) zone: distances where water stays liquid.

Check yourself

Earth is at a distance from the Sun at which water …

If the Earth were much closer to the Sun, the water would …

If the Earth were much farther from the Sun, the water would …

The range of distances over which water stays liquid is called …

• can stay liquid — correct. Yes!
• always evaporates. If it were too close, water would evaporate.
• always freezes. If it were too far, water would freeze.
• freeze. That would happen if it were too far.
• evaporate — correct. Yes!
• stay the same. It would be too hot.
• evaporate. That would happen if it were too close.
• stay the same. It would be too cold.
• freeze — correct. Yes!
• the habitable or Goldilocks zone — correct. Yes!
• the ozone layer. The ozone layer blocks UV rays.
• the geosphere. The geosphere is the solid part of the Earth.