Sedimentary Rocks

QUESTION: Can we date sedimentary rocks using radiometric dating techniques?

ANSWER:

Sedimentary rocks cannot be dated directly using radiometric dating, which is based on the idea that when rocks are in liquid form, their radiometric clock resets. This technique is generally used to date igneous and metamorphic rock, which are rocks that were once melted due to extreme heat and pressure. Radiometric dating determines how long ago the liquid rock solidified into solid rock.

Sedimentary rock on the other hand consists of sedimentary particles which were removed and deposited somewhere else by some sort of fluid (generally wind and water). The sedimentary particles predate the rock which they form. Dating the particles which make up the rock wouldn’t give you the age of the rock itself. In addition, the redeposition process upsets the conditions necessary to achieve accurate results through radiometric dating.

Scientists believe they can indirectly date sedimentary rocks using radiometric dating if they find igneous or metamorphic rock imbedded in or around a sedimentary rock layer. This of course presupposes that radiometric dating works consistently as a dating technique in the first place. The assumptions which underlie radiometric dating are covered in our radiometric dating article published here.