Earth’s Surface

1. Earth’s Surface Chapter 4: A Trip Through Geologic Time Lesson 1: Fossils

2. Fossils • Fossils: preserved remains or traces of living things. • Mostly formed when living things die and are buried in sediment, especially near swamps, lakes, and shallow seas. • Usually hard parts, such as bones, shells, teeth, seeds, and stems.

3. Kinds of Fossils Molds and Casts • Most common type • Preserve fine details • Mold: hollow area in sediment in the shape of an organism • Cast: solid copy of the shape of an organism

4. Kinds of Fossils Petrified Fossils • Petrified means turned into stone • In these fossils, minerals replace all or part of an organism. • this can also happen in tree trunks.

5. Kinds of Fossils Carbon Films • Extremely thin coating of carbon that is left on rocks after they are buried • Preserves very delicate parts of plants and insects.

6. Kinds of Fossils Trace Fossils • Provide evidence of the activities of ancient organisms • Footprints, trails, and burrows are examples.

7. Kinds of Fossils Preserved Remains • Ice, tar, and amber are able to preserve entire organisms.

8. Learning from Fossils • Paleontologists study fossils. • the fossil record provides evidence for past life and shows how organisms have changed over time. • Evolution is the change in living things over time. • Extinct: an organism that no longer exists and will never live on Earth again

9. Learning from Fossils • The fossils left behind give clues about climate and environment – for example, freshwater vs. salt water, cold climate vs. tropical.

10. Earth’s Surface Chapter 4: A Trip Through Geologic Time Lesson 2: The Relative Age of Rocks

11. Relative Age • The age of an event or object in relation other event or objects • Ex) I have an older brother. You know he is older than me but not his exact age.

12. Absolute Age • The actual age of an event or object. • The number of years since a rock has formed. • Example: My older brother is 30 years old.

13. Rock Layers • Law of superposition: in undisturbed horizontal sedimentary rock layers, the older layer is on the bottom and the youngest layer is on the top.

14. Igneous Rock • Magma is molten rock below ground; lava is molten rock above ground. • When lava hardens to make rocks on Earth’s surface, they are extrusive. • Always younger than the rocks below it

15. Igneous Rock • When magma hardens to make rocks below Earth’s surface, they are intrusive. • Always younger than the rock layers around/beneath it.

16. Faults • Fault: a break in Earth’s crust. • A fault is always younger than the rock it cuts through. • Look at the youngest layer cut by the fault to determine its age.

17. Index Fossils • Index fossil: a widely distributed fossil that represents an organism that existed in a certain period of time. • If an index fossil is found in a layer, it helps scientists determine how old the layer is.

18. Unconformity • Unconformity: gap in the geologic record that shows where rock layers are disrupted by erosion. • Folding can cause the rock layers to mix or flip completely, making the youngest layers go to the bottom.

19. Earth’s Surface Chapter 4: A Trip Through Geologic Time Lesson 3: Radioactive Dating

20. Radioactivity • Some elements break down (decay) over time through the process of radioactive decay. • The atoms in the element break down to form atoms of a different element.

21. Half-Life • A half-life is the amount of time it takes for half of the radioactive atoms in an element to decay. • Elements have a unique half life.

22. Using Radioactive Dating • Used to determine absolute ages of rocks: scientists compare the amount of the radioactive element to the amount of the stable element.

23. Using Radioactive Dating • Rocks can be dated with potassium-40, which decays to argon-40 with a half life of 1.3 billion years.

24. Using Radioactive Dating • Carbon-14

25. Earth’s Surface Chapter 4: A Trip Through Geologic Time Lesson 4: The Geologic Time Scale

26. Geologic Time Scale • a record of the geologic events the evolution of life forms as shown in the fossil record. • developed by studying rock layers and using radioactive dating • divisions in the time scale are mostly related to changes in life on Earth

27. Geologic Time Scale • Precambrian time – beginning of time; 88% of Earth’s history; few fossils; ended 542 million years ago. • era – there are three long periods of time called eras; Cenozoic, Mesozoic, and Paleozoic. • periods – the eras are broken into shorter times called periods; for example, the Mesozoic era has the Triassic, Jurassic, and Cretaceous periods.

28. Earth’s Surface Chapter 4: A Trip Through Geologic Time Lesson 4: Early Earth

29. How did Earth Form? • the oldest rocks on Earth are about 4 billion years old • scientists believe the Earth and moon are about the same age; 4.6 billion years old. • scientists believe Earth began as a ball of dust, rock, and ice in space; gravity pulled these together.

30. How did Earth Form? • the Earth heated to the point that it melted; denser materials sank to the bottom (core) and less dense materials hardened over time to create the crust and mantle. • volcanoes and collisions with comets (call of dust, gas, and ice) added CO2, water vapor, and nitrogen to our atmosphere.

31. How did Earth Form? • as Earth cooled, the water vapor condensed into liquid water. • our continents are made of rock; they move slowly Earth’s surface.

32. How did Earth Form? • life was found on Earth about 3.5 billion years ago. About 2.5 billion years ago producers (plants/organisms that make their own food) began to appear.

33. Earth’s Surface Chapter 4: A Trip Through Geologic Time Lesson 6: Eras of Earth’s History

34. The Paleozoic Era • Living organisms were starting to become more complex. • Cambrian Explosion • All animals lived in the sea in the beginning • Invertebrates (no backbone) like jellyfish, worms, and sponges • Brachiopods and trilobites were also common • Vertebrates (backbone) like jawless fish

35. The Paleozoic Era • Plants became more common (ferns) • Fishes evolved over time to have jaws, bones, and scales. • Amphibians (animals that live part of their life in water and part on land) and reptiles became the first animals to reach land. • Insects and winged insects also became more common. • Ended with a mass extinction, wiping out most of the living organisms.

36. The Mesozoic Era • “Age of Reptiles” • Triassic, Jurassic, and Cretaceous Periods • Dinosaurs and mammals first appeared in the Triassic Period. • Several hundred different kinds of dinosaurs came about during the Jurassic Period. • Birds began to replace flying reptiles in the Cretaceous Period. • Flowering plants also appeared during this stage.

37. The Mesozoic Era • This era also ended due to a mass extinction (about 65 million years ago). • It is believed that an asteroid collided with Earth – causing dust and water vapor to block the sun’s light around the Earth. • Plants died and plant-eating animals starved.

38. The Cenozoic Era • In the Quaternary Period, the climate cooled and warmed in cycles, causing ice ages. • The last ice age ended about 10,000 years ago. • Humans appeared during this period. • We are currently still living in this time period; mammals flourished during this time.