WEATHERING AND FOSSILS-II

1. WEATHERING AND FOSSILS-II BY: MS. SAWERA FARRUKH

2. Contents • Rocks • Sedimentary, Igneous, Metamorphic • Rock Cycle • Transportation, Deposition, Sedimentation • Weathering • Physical, Chemical, Biological • Fossil formation and Quarrying • Fossil fuels and their use

3. Weathering • Rocks are of different • shapes and sizes • because they are • changed by the • conditions (wind, • water, ice)in their • environment. • The breakdown (gradual wear away) of rocks into smaller fragments is called weathering.

4. Types of Weathering • There are three types of weathering: • Physical weathering • Wind, Rain, Waves, Freeze-thaw, Onion skin • Biological weathering • Plant roots, Animal burrowing, Movements causing vibrations • Chemical weathering • Acid rain, Rusting

5. Physical Weathering • Physical weathering is caused by physical changes such as changes intemperature, freezing and thawing, and the effects of wind,rainand waves. • Wind, rain and waves • Wind, rain and waves can all cause weathering. The wind can blow tiny grains of sand against a rock. These wear the rock away and weather it. Rain and waves can also wear away rock over long periods of time.

6. Exfoliation or onion-skin weathering • Exfoliation or onion-skin weathering (Changes in temperature) • This type of physical weathering happens a lot in deserts, because it is very hot during the day but very cold at night. • When a rock gets hot it expands a little, and when a rock gets cold it contracts a little. • If a rock is heated and cooled many times, cracks form and pieces of rock fall away.

7. Exfoliation or onion-skin weathering • During the day, the sun heats up the surface of the rock causing the rock to expand. • During the night the rock cools down and contracts. • As the rock keeps expanding and contracting, pieces of surface of rock begin to flake and fall off.

8. Freeze-thaw weathering • Freeze-thaw • Water expands slightly when it freezes into ice. • If water gets into a crack in a rock and then freezes, it expandsandpushesthe crack further apart. • When the ice melts later, water can get further into the crack. When the rockfreezesagain, it expands and makes the crack evenbigger. • This process can continue until the crack becomes so big that a piece of rock falls off.

9. Freeze-thaw weathering • Water finds its way into small cracks in the rock. • Atnight-time, when the temperature drops to 0°Corbelow,the water in the crack freezesforming ice. • The water expands as it freezes creating huge forces on the surrounding areas of the rock which make the crack get bigger.

10. Freeze-thaw weathering • During the day, when the temperature warms up again, the frozen water thaws. • At night-time this water freezes again. • This cycle is repeated over and over again and the huge forces created cause more cracks to appear in the rock. • Finally a fragment of the rock breaks away completely.

11. Biological Weathering Animalsandplantscan wear away rocks. This is called biological weathering. • Burrowing • Animals such as rabbitscan burrow into a crackin a rock, making it biggerand splitting the rock. • Movements • People and animals can even cause biological weathering just by walking. Over time, paths in the countryside become damaged because of all the boots and shoes wearing them away.

12. Biological Weathering • Plants • Plant roots and shoots can • grow in tiny cracks. • As they grow bigger, they • push open the cracks and • make them wider and deeper. • Eventually pieces of rock • may fall away. • The weeds or bushes growing through cracks in the pavement and disused buildings in the countryside are it’s examples.

13. Chemical Weathering • The weathering of rocks by chemicals is called chemical weathering. Acid rain makes chemical weathering happen more quickly. • Some types of rock are not easily weathered by chemicals. Granite and Gabbro are hard rocks that are weathered only slowly. • Some types of rock are easily weathered by chemicals. Limestone and Chalkmake new soluble substances that are washed away easily and the rock is weathered.

14. Chemical Weathering • Chemical weathering can hollow out cavesform and make cliffsfall away. • The buildings and statuesmade from rock are damaged as a result.

15. Chemical Weathering • Slow chemical weathering • Rainwater is naturally acidic because carbon dioxide in the air reacts with rainwater to form carbonic acid. • This type of acid rain is weakly acidic and reacts slowly with minerals in the rock.

16. Chemical Weathering • Rapid chemical weathering • The burning of fossil fuels produces oxides of sulphur and nitrogen which make rainwater strongly acidic. • This type of acid rain reacts quickly with minerals and weather rock more rapidly.

17. Fossils

18. What are Fossils? • Fossil is a Latin word which means “something that has beendug up”. • These are defined as the remains and the preserves of the plants and animals that existed many million years ago. In other words, fossils are simply the traces of the organisms of the past. • The study of the discovered fossils has given the information about the evolution and the factors that led to evolution of the past organisms.

19. How are Fossils formed?

20. Fossils in Sediments • By sedimentation • During the formation of sedimentary rocks, the dead animals or plants present in the sea, and of the land thatare carried to the sea or large lakes by river, sink down and get buried in the rocks. • Now an entire organism or a part of its body has become buried in the deeper sediments of the earth, which cuts the supply of oxygen for them and thus prevents their decay, resulting in the formation of fossils.

21. Fossils in Sediments

22. Fossils in Ice • Freezing (Refrigeration) • This is the best means of preservation, but it happens only rarely as the animal must be continually frozen from the time of death until discovery. That limits the possibilities to cold hardy animals from the last ice age. • Specimens with flesh, skin, and hair intact have been found. Some were found with food still in the mouth and stomach. • Discoveries of mammoth and wooly rhinoceros found in ice were made from Alaska and Siberia.

23. Fossils in Ice

24. Mummified Fossils • Drying (desiccation) • TheMummified bodies of animals including humans have been discovered in arid parts of the world. • The soft tissues including skin and organs are preserved for thousands of years if they are completely dried.

25. Fossils in Asphalt • Asphalt • The tar pits were formed by crude oil seeping through fissures in the earth and when the lighter elements of the oil evaporate leaving thick sticky asphalt which is an excellent preservative. • Bones, teeth, shells, the exoskeletons of insects, and even some plant seeds have been pulled from the pits.

26. Fossils in Amber • Amber • Insects, spiders, and even small lizard have been found, nearly perfectly preserved in amber. • Picture this scenario: A fly lands on a tree branch in an area while looking for food. It steps and gets trapped in sticky sap that the tree has made to protect itself from fungal infection.