There is no model visible, but the main theory as to how an asteroid/meteor impact would cause a mass extinction is that the force of the projectile landing onto the surface of the earth would launch so much debris and material into the atmosphere that it would block out most if not all light from the sun, leading to a inevitable food pyramid crash. As the producers die and become harder and harder to find, primary consumers decline which leads to the decline of secondary consumers, and so on until you reach the apex predators in the ecosystem(s). Hope this helped!