How does the release of an alpha particle affect a mass number? atomic number?

Which of the following is true about fossils? a. fossils found in lower layers of sedimentary rock are older than fossils found in upper layers of sedimentary rock. b. fossils found in lower layers of sedimentary rock are as old as fossils found in upper layers of sedimentary rock. c. the relative age of fossils cannot be determined from their position in sedimentary layers.