Destroying instantiated game objects from prefab when coliding with the ground

Hi, im working on a game where you need to dodge asteroids that fall from the sky. I made a random spawner script with empty game object. from a youtube tutorial. Now I dont know how to destroy asteroids when they collide with the ground. Im new at making games. I tried many diferent options.Puting destroyer scripts i found online in the spawner script, didnt work. making a new script and adding it to my asteroid prefab, didnt work. I dont know what to do. im using this script as a destroying script :

using UnityEngine;
using System.Collections;

public class Destroyer : MonoBehaviour
    void OnCollisionEnter(Collision other)

If anyone can help me i would be very grateful!

Assuming this script is attached to the asteroid prefab it should work I think.

Does the asteroid prefab and the ground have collider components? (such as sphere collider or box collider?)