Right or wrong theory?

This theory (large meteoroid or comet impact)is teach years in the schools and even universities.regarding there's no sign of such impact in the earth body and no sign of meteoroid large in that scale. .Bones founded are cause of despoil in the soil without any burn signs ,that mean cause should be something more like virus (group mass bones)The most the Dino bones were found close to the lakes of water ,which no sign of the tooth or damages such as fight or burn was found in the bones .There are many causes that can kill animal in a large scale ,such as oxygen level ,water contamination ,diseases,sulfur gas level .Oil spill,Heat struck and as they live close together on group ,contamination act faster.Other discovery show that bones were found in different layer of the soil with years distance ,which mean is a point of return or immigrant for the dinosaurs in a particular time or season .A mass dead like fishes in last decade caused by ocean contamination show that mass extinction can be take place without any physical damage to the earth structure .Is in study that level of the CO2 if rise above the normal can cause mass excitation as well (hyperventilation).Also sun radiation can cause Nero damage to point which nerve system completely get disable and cause imminent dead in manner of the minutes .