Kumar is studying how Earth is warmed by sunlight. The following shows his model of the sun and Earth.
Which process is mostly responsible for warming the soil in Kumar's model?
1. Conduction between the lamp and the soil causes the soil to warm.
2. Convection currents between the lamp and the soil cause the soil to warm.
3. Expansion of particles in the soil causes the soil to warm.
4. Radiation from the lamp reaches the soil and causes the soil to warm.