Weathering Processes will dominate lab this week - it will be very helpful to you if you read the background information about this activity before coming to class.
Weathering: breaking down rocks at the Earth's surface
Mechanical weathering: breaking down into smaller pieces causes size and shape changes
abrasion: bits of rock knock against each other knocking off the corners and edges; as when sediment bumps against each other in a stream or when being washed by the waves.
ice wedging: when water freezes it expands by 9% of its volume. If water freezes in a crack in a rock, it will expand wedging the rock apart such that many seasons of water freezing and thawing in fractures will end up breaking the rock apart.
organic wedging: when seeds fall into cracks in a rock, they often grow there forcing the rock apart as the plant gets bigger.
Chemical weathering: the rock is "attacked" by acidic water over time (rain water is slightly acidic). This causes most of the minerals to break down producing some solid products (clay for example) and ions that are carried away by the water. Resistant minerals (like quartz) will remain behind, or are later washed away with the water.
dissolution: certain minerals will dissolve completely away, leaving nothing behind. The dissolved mineral is carried away as ions in the water. Calcite (calcium carbonate) is particularly susceptible to dissolution. Most caves are formed in limestone, a sedimentary rock made of calcite that dissolves away, leaving caves behind.
oxidation: minerals containing iron (Fe) will oxidize (form iron oxide, like rust) and produce reddish colors (often forming the mineral, hematite an iron oxide). Many dark colored minerals contain iron (such as hornblende, biotite, olivine, magnetite, to name a few)
production of clay minerals: minerals containing aluminum (Al) can be attacked by acidic water (rain water is slightly acidic) producing clay (aluminum enriched minerals) as a solid product. Elements in the original mineral that don't become part of the clay are carried away by the water as ions. The clay may remain behind in the soil that forms on top of the weathering rock, or it may be washed away during rain storms and carried downstream suspended in rivers (that's what make some rivers look brown).
Mechanical weathering aids chemical weathering by breaking up the rock so that more of the rock is exposed to the water for chemical weathering (breaking up the rock increases the surface area over which the slightly acidic water may act to do chemical weathering).
This applies another of Page Keeley's formative assessment techniques (called "Odd One Out") to review the material that you hopefully learned during the weathering processes activity
You will be examining photographs of old tombstones and using what you learned about weathering to put them in the correct order from oldest to youngest.
Read through the activities in your manual, attempt to answer the assignment questions, turn it in prior to the next class. Contact Dr. Munn to arrange to make up the quiz that you missed (this must be done sometime before the next class). Worksheets collected for this lab will be listed on the Lab Schedule page and must be turned within a week. Click here for the syllabus information about missing class. Here are more specifics about the worksheets that were collected (all of these are from your manual and reading the background material for each activity should help you to answer the questions):
• p.66 (questions 3, 5-7 of the Shake it Up activity)
• p.67 (questions 5-6 of the Ice Power activity)
• p.68 (questions 10-11 of the Mighty Plants activity)
• p.70 (questions 1-5 of the Fizzies activity)
• p.71-72 (questions 6-7 and 8-11of the Crumbling Granite activity)
• p.76 (Odd One Out: Weathering)
• p.78-80 (Tomstone Detectives - you can download the tombstone pictures on SacCT (once you get there, click on 'pdf documents' in the left sidebar).