The subarachanoid space lies between the arachnoid and pia mater. It is filled with cerebrospinal fluid. All blood vessels entering the brain, as well as cranial nerves pass through this space. The term arachnoid refers to the spider web like appearance of the blood vessels within the space.
Why do biologists organize living things into groups? What do the levels of classification indicate about the relationship between organisms? What characteristics are used to classify organisms into domains and kingdoms? What is the scientific study of how living things are classified called? Taxonomy
Obviously, the 'study of the earth' is quite a broad concept, so there are many subdisciplines within the Earth sciences. In general, geology is the scientific study of the earth- the material of which it is made, the processes that act on these materials, the products formed, and the history of the planet and its life forms since origin. Geology now includes the study of other planets as well.