A geologist studies layered rock to determine its age. Bacteria fossils from the Precambrian age are found in the rock’s upper layers, but no fossils are found in the rock’s bottom layer. Which of these conclusions about the rock is bet supported by evidence?

The bottom layers of the rock could have formed before life occurred.

Explanation:
The bottom layers of the rock could have formed before life occurred because there is no fossil is present. If there is life at that time so the fossils are present at the bottom layer so the absence indicates that is no life present at that time. The bottom layer is older than the upper layer so that's why fossils of bacteria are found in the upper layer of the rock.

C. Because bacterial fossils are found only in the upper layers, scientists can conclude that these bacteria evolved towards the end of Precambrian time.

There’s two different types of answers for this question so I just put both of them. Hope it helps : )

For cyclohexane compounds drawn in a chair conformation:   -axial bonds are vertical  -equatorial bonds are parallel to two bonds within the ring.  thus, as i assume the chair conformation is drawn:   -the x group is in an axial position, as are the five other vertical bonds.  -three axial bonds are on the top face of the ring  -the other three axial bonds are on the bottom face  the position of the second substituent on each ring carbon is equatorial.  gauche groups must be on an adjacent carbon such as carbon 6 and carbon 2, and also gauche groups are rotated by 60 degrees relative to each other.  drawing the newman projections for c1–c2 and c1–c6 aids in visualizing the groups that are gauche to the y group on c1.  click this link and watch some academic videos that may you more understand the topic