They use the process known as decomposition- much like the name!
The meteorite was probably 1<span>0 to 15 km (6.2 to 9.3 mi) wide</span> and affected the entire planet through a proces called "impact winter". As the name suggests, an impact winter is a period of low temperature produced by a huge cloud of ash and dust that blocks sunlight. Since sunlight is essential for plants to survive, if the sun rays are blocked by this cloud, all animals that depend on those plants (including dinosaurs) will die. The meteorite could have created such a cloud upon hitting the earth.
Plasma cells are designed to churn out Antibodies. These are proteins that have a variable region which is complementary ( perfect shape fit) for the virus' antigen and can therefore bind to the antigen, making the virus harmless or tagging it to be consumed by a phagocyte.
Whatever you do do not click on that link