Because, it is the process by which they make or produce their food with the help of sunlight, water and carbon dioxide.
If photsynthesis is not there then there would be no production of food and ultimatley plants will die.
Complementary mRNA strand would be the following:
AUCAUCAUC.
3 Repeating codons of AUC, on the mRNA strand.
Certain fossils, called index fossils, help geologists match rock layers. To be useful as an index fossil, a fossil must be widely distributed and represent a type of organism that existed for a brief time period. Index fossils are useful because they tell the relative ages of the rock layers in which they occur.