Do Now

1. Do Now • What are the two types of metamorphism • What type of rock is “born from fire” as its Latin name suggests? • How can a metamorphic rock become an igneous rock?

2. Objective • SWBAT: Describe how a fossil is formed • Compare and contrast mechanical and chemical weathering

3. Fossils • Fossilization - refers to a variety of often complex processes that enable the preservation of organic remains within the geological record. • Conditions: • rapid and permanent burial • oxygen deprivation • continued sediment • absence of excessive heating or compression

4. Fossils Usually formed beneath sediments deposited beneath water Why do you think fossils are not as common on land as they are in the marine environment?

5. Fossil Formation • Fish returns to its birth place to spawn

6. After spawning the fish dies and sinks to the seafloor.

7. After several weeks the soft body tissues have mostly decayed

8. Nearby tectonic activity causes sediment to mobilize and buries the specimen

9. Several months pass and all that remains of the buried fish is its skeleton

10. As times passes more sediment accumulates above the fish and the skeleton is gradually compressed and permineralised.

11. Permineralization • Process of fossilization • Mineral deposits form internal casts of organisms • Minerals fill the spaces within organic tissue

12. Permineralization • Silicifaction- Silicate minerals from weathering • Minerals permeate pores and cells of dead organisms and becomes a gel. • Gel will dehydrate over time and form a crystal structure that is an internal cast of the organism • Most common type

13. Over time the rock is distorted and uplifted by geological forces associated with continental movement, raising it above sea level

14. The uplifted rock is exposed to weathering and gradually erodes away, eventually exposing the tip of the fish's skull at the surface.

15. A palaeontologistrecognises the fish by the small area of skull exposed and begins to carefully extract the specimen.

16. A Pomognathus fish from Houghton Quarry - the skull is clearly visible, and what parts of the skeleton remain are obscured within the chalk matrix.

17. Your Turn…. • You and a friend are walking along Herne Bay when your friend discovers something on the ground. • Knowing you have strong science skills, your friend shows you the amazing discovery…..

18. Wow! What a find! Your friend has stumbled across a fragment of a turtle shell. • Write out an explanation to your friend about how this fossil was formed.

19. Project • Journey of a sedimentary rock • Due friday

20. Objective • SWBAT: Compare and Contrast Mechanical and Chemical weathering

21. Weathering: the disintegration, or breakdown of rock material

22. Weathering • Mechanical • no change in chemical composition--just disintegration into smaller pieces • Chemical • breakdown as a result of chemical reactions • CaCO3+CO2+H2O --> Ca2+ + 2HCO3-

23. Mechanical Weathering • Physical breakup • pressure release • water: freeze - thaw cycles • crystallization of salt in cracks • thermal expansion and contraction • All this increases the total surface area exposed to weathering processes.

24. Mechanical Weathering Exfoliation: Rock breaks apart in layers that are parallel to the earth's surface; as rock is uncovered, it expands (due to the lower confining pressure) resulting in exfoliation.

25. Mechanical Weathering Weathering

26. Half Dome, Yosemite, CA Stone Mountain, GA

27. Sheet Joints(Exfoliation)

28. Exfoliated Domes, Yosemite

29. Frost Wedging: rock breakdown caused by expansion of ice in cracks and joints

30. Stone Mountain, Georgia, showing the product of exfoliation due to unloading Stone Mountain, GA

31. Shattered rocks are common in cold and alpine environments where repeated freeze-thaw cycles gradually pry rocks apart.

32. Thermal expansion due to the extreme range of temperatures can shatter rocks in desert environments. Repeated swelling and shrinking of minerals with different expansion rates will also shatter rocks. Weathering

33. Role of Physical Weathering • Reduces rock material to smaller fragments that are easier to transport 2) Increases the exposed surface area of rock, making it more vulnerable to further physical and chemical weathering

34. Surface Area and Weathering

35. Rates of weathering Joints in a rock are a pathway for water – they can enhance mechanical weathering

36. Chemical Weathering • Definition: transformation/decomposition of one mineral into another • Mineral breakdown • carbonate dissolves • primary minerals --> secondary minerals (mostly clays) • Net loss of elements retained in the soil.

37. Chemical Weathering • Definition: transformation/decomposition of one mineral into another • Mineral breakdown • carbonate dissolves • primary minerals --> secondary minerals (mostly clays) • Net loss of elements retained in the soil.

38. Chemical Weathering • Water is the main operator: • Dissolution • Many ionic and organic compounds dissolve in water • Silica, K, Na, Mg, Ca, Cl, CO3, SO4

39. Dissolution H2O + CO2 + CaCO3 --> Ca+2 + 2HCO3- water + carbon dioxide + calcite dissolve into calcium ion and bicarbonate ion Biological activity in soils generates substantial CO2 Bicarbonate is the dominant ion in surface runoff.

40. Chemical Weathering Solution: process by which rock is dissolved in water • Is strongly influenced by pH and temperature • When water becomes saturated, chemicals may precipitate out forming evaporite deposits. • Calcium carbonate (calcite, limestone), sodium chloride (salt), and calcium sulfate (gypsum) are particularly vulnerable to solution weathering.

41. Biological Weathering • Can be both chemical and mechanical in nature. • roots split rocks apart • roots produce acids • that dissolve rocks. • tree throw • burrowing animals

42. Weathering Rates of weathering • Climate • Temperature and moisture characteristics • Chemical weathering • Most effective in areas of warm, moist climates – decaying vegetation creates acids that enhance weathering • Least effective in polar regions (water is locked up as ice) and arid regions (little water) • Mechanical weathering • Enhanced where there are frequent freeze-thaw cycles

43. Mechanical and Chemical Weathering • Fracturing, disintegration caused by mechanical weathering exposes more surface area. • Greater surface area, means more places for chemical action to occur.

44. Venn diagram • Create a venn diagram to compare and contrast mechanical and chemical weathering

46. Exit Ticket • Name 3 conditions necessary for fossil formation • Describe exfoliation. Include what type of weathering it is (mechanical or chemical). • How does weathering affect surface area?