The cretaceous-tertiary extinction was most likely caused by an asteroid hitting the earth volcanism both a and b none of the above

The correct answer is option A, an asteroid hitting the earth

Reason -

The extinction event of Cretaceous is considered as a mass extinction process in which near about 3/4th of the species on planet earth became extinct. The researches conducted (found in geologic record) to study the cause of this massive extinction event,  revealed presence of  iridium metal on the Earth crust which is a rare metal and is usually found in the asteroids or comets. Thus,  hitting of planet earth by the asteroids or comets can be considered as a cause of this massive extinction.

the relative standard reduction potential of the half-cell in which reduction occurs; more positive than the other half-cell. reduction is a chemical process in which electrons are added to an atom or an ion; it always occurs accompanied by oxidation of the reducing agent.