Not necessarily primitive, but definitely older.
Rock Bottom
That would be, you get, rock bottom
The lowest number on the Ritcher scale is a 1.0. A 1.0 is generally not felt at all. The highest number is a 10 on the Ritcher scale.
Stratus clouds are generally the lowest clouds in the atmosphere, usually 1,000 - 2,000 feet up.
A valley is a continuous depression generally between two ranges of hills. It may have a stream linking its lowest points.
primitive
They would be the most primitive because they would be the oldest fossils.
353 has primitive roots because it is a prime number. (Not all numbers have primitive roots) It has 160 primitive roots. Generally however when we talk about THE primitive root we are talking about the lowest. So, starting at 2,3,4,5, ...... create a spreadsheet where the columns are the numbers being tested and the rows contain the powers of these numbers modulo 353 up to 176 (=352/2).The first column not containing a 1. is the lowest primitive root.
Rock Bottom
in the lowest layers of rock
That would be, you get, rock bottom
Generally, the lowest.
Assuming the layers aren't deformed, the lowest deposition layers are the earliest. Later deposition layers accumulate on top of the earlier layers. Thus, the lowest layers have the earliest fossils, and the highest layers have newer fossils. By comparing the features of early and late fossils of a species, you can determine some of its evolutionary changes. Of course, not all features survive in a fossil - soft tissues, for example.
Fossils of armored fish, corals, shellfish, and snails have been found in the Grand Canyon.
Central uplands
it is generally the lowest pulley on the front of the engine.
This will generally happen in the dryest part of the year.