The above picture shows the oldest material on the bottom, younger material on top and then the youngest material. Meaning what's oldest will be on top and the youngest on the bottom.
The youngest cuts all layers which means those layers were there before the youngest layer cut them. So when in the field observing rocks and trying to relatively date you can use techniques such as grading (in sedimentary rocks) to help tell which way is up.
This lesson will define a fossil, look at different types and characteristics of fossils, and then describe how fossils are formed.
Why It's Important: Among other things, the TREM2 protein is involved with phagocytosis by microglia.
Relating a variant in this gene/protein to AD strongly supports the involvement of microglia and the immune system in the pathogenesis of this important disease and also adds another factor to genetic risk for AD.
This article provides the evidence for doing so and shows how it improves the quality of care we give our patients, particularly in the areas of complex symptom management — for example, treating non-pain symptoms such as nausea, delirium, and fatigue; communication (that is, responding to emotion and demonstrating empathy); establishing goals of care; and facilitating medical decision-making.
Results: Using different approaches, two groups independently found that a variant (R47H) in the TREM2 (triggering receptor expressed on myeloid cells 2 protein) gene is a rare but strong genetic risk factor for late-onset Alzheimer's disease (AD) in the general population.