The Blue Marble
Earth is the only planet in our solar system where life thrives. From space, it looks like a blue marble because 70% of its surface is covered with water. But what lies beneath?
Structure of the Earth
If Earth were the size of an apple, the crust (where we live) would be as thin as the apple’s skin.
Earth vs. The Solar System
Let’s compare Earth with its neighbors.
| Planet | Avg Temp () | Has Atmosphere? | Status |
|---|---|---|---|
| Mercury | 170 | No | Too Hot / No Air |
| Venus | 450 | Yes (Thick) | Hottest Planet |
| Earth | 15 | Yes (Just Right) | Life Exists |
| Mars | -60 | Yes (Thin) | Too Cold |
Warning
Why is Venus hotter than Mercury? Mercury is closer to the Sun, so it should be hotter. However, Venus is the hottest planet (). This is because Venus has a thick atmosphere made mostly of Carbon Dioxide (). This creates a runaway Greenhouse Effect, trapping huge amounts of heat.
The Greenhouse Effect
On Earth, the greenhouse effect is actually helpful (in moderation). Without it, Earth would be too cold for life.
- Solar radiation enters the atmosphere.
- Earth warms up and releases heat.
- Greenhouse gases (like ) trap some of this heat.
- This keeps the planet warm enough for liquid water.