Final answer:
True, greenhouse gases are critical for retaining sufficient heat on Earth's surface to allow for liquid water, essential for life. The greenhouse effect raises Earth's average temperature above freezing, unlike Mars where water froze or Venus where water was lost due to a runaway greenhouse effect.
Step-by-step explanation:
1) True. Without greenhouse gases, Earth's surface would indeed be too cold for liquid water. The current greenhouse effect on Earth increases the surface temperature by approximately 23 °C. If it weren't for this effect, our planet would have an average surface temperature around -18 °C, which is well below the freezing point of water. This would result in Earth being locked in a global ice age, with oceans permanently frozen.
The importance of the greenhouse effect can be observed by looking at our neighboring planets. For instance, Mars lost its substantial greenhouse effect when its atmospheric CO₂ diminished, leading to the freezing of its water resources. Venus, conversely, has an excessive greenhouse effect creating surface temperatures too high to support liquid water.
It is the delicate balance maintained by Earth's atmosphere that allows for the presence of liquid water, which is essential for life as we know it. Earth is currently the only known planet in our solar system where liquid water exists freely on its surface, signifying the critical role the greenhouse effect plays on our planet.