Stratigraphy is the study of sedimentary rock layers.
According to the law of superposition, as long as an area remains undeformed by outside forces, the deeper you go down through the layers of rock, the older they are.
The age of the fossil must be determined so it can be compared to other fossil species from the same time period.
Understanding the ages of related fossil species helps scientists piece together the evolutionary history of a group of organisms.
For example, based on the primate fossil record, scientists know that living primates evolved from fossil primates and that this evolutionary history took tens of millions of years.
By comparing fossils of different primate species, scientists can examine how features changed and how primates evolved through time.
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Because of the alternation between dark and light sediments we can use each dark band as a marker for one year.VARVES ARE LAYERS OF LIGHT AND DARK SEDIMENT THAT SHOW YEARLY CYCLES. Each spring or summer when the glacier was melting the glacier deposits a ton of sediment it was carrying into strems of water that are melting off of it.When the meltwater reaches a lake the heaiest sediments (sand and silt) sink to the bottom quickly and eventually formed thick layers of light colored rock.So I’ve got probably ten more demos that I’ve just been hanging on to.Nothing full again, probably just minute and a half ideas.When they break and engulf chunks of sedimentary rocks, it's called stoping. The original rock layers around subsidence areas are called wall rocks and the layers that xenoliths came from are called parent rocks.