Step 1: List the atmospheric layers.
Going up from the ground, the layers are troposphere, stratosphere, mesosphere and thermosphere.
Step 2: Find the lowest layer.
The layer that touches the Earth's surface and sits below all the others is the troposphere.
Step 3: Recall what it holds.
The troposphere holds almost all the water vapour, clouds and dust of the atmosphere.
Step 4: Link it to weather.
Because clouds and moisture live here, rain, storms and nearly all weather happen in this layer.
Step 5: Reject the higher layers.
The stratosphere, mesosphere and thermosphere are above and are mostly clear of weather activity.
Step 6: Conclusion.
The lowest layer where all weather occurs is the troposphere.
\[ \boxed{\text{Troposphere}} \]