Which of the following pairs of half-reactions would have a negative total reduction potential?
A. Copper (Cu) reduced, zinc (Zn) oxidized
B. Hydrogen (H) reduced, sodium (Na) oxidized
C. Mercury (Hg) reduced, iron(II) (Fe) oxidized
D. Silver (Ag) reduced, gold (Au) oxidized

In order to determine the rate at which the sediment layers were deposited

Explanation:

Iridium is an important element that belongs to the Platinum group and they are dominantly present in the asteroids and comets. They are the key evidence that suggests the occurrence of an asteroidal impact or a mass extinction event that has taken place in the geological past.

The presence of Iridium mixed with the clay sediments in the boundary between the Cretaceous and Tertiary (K-T boundary) suggested the mass extinction event that wiped out numerous life forms from the earth.

The famous scientist Dr. Luis Walter Alvarez suggested measuring the concentration of Iridium in this K-T boundary in order to determine the rate at which these sediment layers were deposited. They were able to determine that these Iridium elements were present due to the asteroid impact on earth, that wiped out the dinosaurs from the earth. They also considered that this element can be produced from the eruptions of volcanoes.