Fossils

1. Fossils

2. Traces of the Distant Past Paleontologists, scientists who study fossils, can learn about extinct animals from their fossil remains. Scientists can learn how dinosaurs looked and moved using fossil remains.

3. Formation of Fossils Fossils are the remains, imprints, or traces of prehistoric organisms. Fossils are evidence of not only when and where organisms once lived, but also how they lived.

4. Formation of Fossils For the most part, the remains of dead plants and animals disappear quickly. Scavengers eat and scatter remains of dead organisms. Fungi and bacteria invade, causing the remains to rot and disappear.

5. Conditions Needed For Fossil Formation Whether or not a dead organism becomes a fossil depends upon how well it is protected from scavengers and agents of physical destruction, such as waves and currents. One way a dead organism can be protected is for sediment to bury the body quickly.

7. Conditions Needed For Fossil Formation Organisms have a better chance of becoming fossils if they have hard parts such as bones, shells, or teeth. Most fossils are the hard parts of organisms, such as fossil teeth.

8. Types of Preservation—Mineral Replacement Most hard parts of organisms such as bones, teeth, and shells have tiny spaces within them. If the hard part is buried, groundwater can seep in and deposit minerals in the spaces. Permineralized remains are fossils in which the spaces inside are filled with minerals from groundwater.

9. Types of Preservation—Mineral Replacement Sometimes minerals replace the hard parts of fossil organisms. For example, a solution of water and dissolved silica might flow into and through the shell of a dead organism. If the water dissolves the shell and leaves silica in its place, the original shell is replaced.

10. Carbon Films Sometimes fossils contain only carbon. Fossils usually form when sediments bury a dead organism. As sediment piles up, the organism’s remains are subjected to pressure and heat. These conditions force gases and liquids from the body. A thin film of carbon residue is left, forming a silhouette of the original organism called a carbon film.

11. Over millions of years, these deposits become completely carbonized, forming coal. Coal In swampy regions, large volumes of plant matter accumulate.

12. Molds and Casts Impressions form when seashells or other hard parts of organisms fall into a soft sediment such as mud. Compaction, together with cementation, which is the deposition of minerals from water into the pore spaces between sediment particles, turns the sediment into rock. Other open pores in the rock then let water and air reach the shell or hard part.

13. Molds and Casts • The hard part might decay or dissolve, leaving behind a cavity in the rock called a mold. • Later, mineral-rich water or other sediment might enter the cavity, form new rock, and produce a copy or cast of the original object.

14. Origin of molds and casts. • (A) Formation of a mold. • (B) Formation of a cast.

15. Original Remains Sometimes conditions allow original soft parts of organisms to be preserved for thousands or millions of years. For example, insects can be trapped in amber, a hardened form of sticky tree resin. Some organisms have been found preserved in frozen ground. Original remains also have been found in natural tar deposits.

16. Trace Fonts Trace fossils are fossilized tracks and other evidence of the activity of organisms. In some cases, tracks can tell you more about how an organism lived than any other type of fossil.

17. Trails and Burrows Other trace fossils include trails and burrows made by worms and other animals. These too, tell something about how these animals lived. For example, by examining fossil burrows you can sometimes tell how firm the sediment the animal lived in was.

18. Coprolites A coprolite is fossilized feces. Coprolites are classified as trace fossils as opposed to body fossils, as they give evidence for the animal's behavior (in this case, diet) rather than morphology.

19. Index Fossils Index fossils are remains of species that existed on Earth for relatively short periods of time, were abundant, and were widespread geographically. Because the organisms that became index fossils lived only during specific intervals of geologic times, geologists can estimate the ages of the rock layers based on the particular index fossils they contain.

20. Similarity of fossils suggests similarity of ages, even in different rocks widely separated in space.

21. Index Fossils Index fossils allow scientists to obtain relative ages for different rock layers. The estimated or relative age of a rock is obtained as the time interval where ranges of fossils overlap.

22. Relative Ages The relative age of something is its age in comparison to the ages of other things. Geologists determine the relative ages of rocks and other structures by examining their places in a sequence. Relative age determination doesn’t tell you anything about the age of the rock layers in actual years.

23. Fossils and Ancient Environments Scientists can use fossils to determine what the environment of an area was like long ago. Using fossils, you might be able to find out whether an area was land or whether it was covered by an ocean at a particular time.

24. Fossils and Ancient Environments Fossils also are used to determine the past climate of a region. For example, rocks in parts of eastern United States contain fossils of tropical plants. Because of the fossils, scientists know that it was tropical when these plants were living.

25. Shallow Seas When the fossil crinoids were alive, a shallow sea covered much of western and central North America. The crinoid hard parts were included in rocks that formed from the sediments at the bottom of this sea.

26. Absolute Ages Absolute age is the age, in years, of a rock or other object. Geologists determine absolute ages by using properties of the atoms that make up materials. Atoms of the same element can have different numbers of neutrons; the different possible versions of each element are calledisotopes.

27. Absolute Ages Absolute age is usually measured using radiometric dating: Radiometric dating (often called radioactive dating) is a technique used to date materials such as rocks, usually based on a comparison between the observed abundance of a naturally occurring radioactive isotope and its decay products, using known decay rates.

28. Radiometric dating http://en.wikipedia.org/wiki/Image: Henri_Becquerel.jpg In 1896, Discovery of radioactivity paved the way for the precise dating of events in the geological record Henri Becquerel (1852-1908)

29. Alpha radiation Radioactive ‘parent isotopes’ spontaneously emit protons and neutrons and decay into ‘daughter isotopes’. E.g., Uranium-238 decays into Lead-206

30. Alpha and Beta Decay In some isotopes, a neutron breaks down into a proton and an electron. This type of radioactive decay is called beta decay. Other isotopes give off two protons and two neutrons in the form of an alpha particle.

31. The rate of decay from parent to daughter isotope depends on its half life. The half life is the amount of time needed for half the parent isotope to decay to daughter isotope

32. Geological timescales Decay series Half life 40K to 40Ar 1250 Ma 147Sm to 143Nd 1060 Ma 235U to 207Pb 704 Ma 238U to 206Pb 4468 Ma 14C to 14N 5370 years Archaeology Different radioactive isotopes have different half lives Isotopes with long half lives are useful for dating old rocks. It is important to use the right tool for the right job

33. Radiocarbon and Tree- Ring Dating Methods Carbon-14 dating is based on the ratio of C-14 to C-12 in an organic sample. Valid only for samples less than 70,000 years old. Living things take in both isotopes of carbon. When the organism dies, the "clock" starts. Method can be validated by cross-checking with tree rings

35. Age Determination Aside from carbon-14 dating, rocks that can be radiometrically dated are mostly igneous and metamorphic rocks. Most sedimentary rocks cannot be dated by this method. This is because many sedimentary rocks are made up of particles eroded from older rocks.

36. Origin of Earth 4.6 billion years ago The sun and the planets coalesced out of a vast cloud of gas and dust The Earth was a hot glowing ball of white hot gases. Particles of gases were compressed together, giving off heat. Gases cooled down so the Earth contracted and gases turned to liquids. Heavy materials went to the center of the Earth and a liquid material went to the center.

37. The Moon 4.527 billion years ago A large impact on Earth heated up and was flung into space into the orbit of the Earth. The moon’s gravitational pull might have made Earth a livable planet by making the Earth’s axial tilt constant, which made the Earth keep a stable climate.

38. Moon’s Formation According to the "giant impact" theory, the young Earth had no moon. At some point in Earth's early history, a rogue planet, larger than Mars, struck the Earth in a great, glancing blow. Instantly, most of the rogue body and a sizable chunk of Earth were vaporized. The cloud rose to above 13,700 miles (22,000 kilometers) altitude, where it condensed into innumerable solid particles that orbited the Earth as they aggregated into ever larger moonlets, which eventually combined to form the moon.

39. The Creation of the Moon About 4.527 billion years ago • A plant like object crashed into the earth and part of it shifted away

40. History of the Earth The Earth's crust, its outermost layer, formed about 4.44 billion years ago, roughly 100 million years after the formation of the Earth itself. Prior to 4.44 billion years ago, the Earth's crust was entirely molten, due to residual heat from the planet's initial collapse. Evidence that the Earth's crust cooled within 100 million years comes from measurements of hafnium levels in the Jack hills in Western Australia, one of the oldest areas of exposed crust today. During the initial formation of the Earth's crust, an event known as the Iron Catastrophe occurred, where the denser elements of the Earth's composition, such as iron and nickel, sank to its core, while the lighter elements, like silicon, formed a crust at the top. The crust began to cool when the Earth was at least 40% of its current size, possessing enough gravity to hold down an atmosphere containing water vapor. Much of this early water vapor would have come from comets.

41. Ancient landscape Massive volcanoes and lava fields dominated the landscape

42. Water Was Formed On Earth About 3.8 billion years ago The crust formed over the liquid material. The crust cracked, revealing water underneath and water vapor was formed. Water vapor formed clouds and water was pulled towards Earth’s surface in rainfall making lakes and oceans.

43. Life on Earth 3.5 billion years ago Scientists think that the first single cell organisms lived near hydrothermal vents in the oceans because of the chemicals by the vents. 3 500 million years ago Prokaryotes were started. 1 800 million years ago Complex single-celled life appears. 1 500 million years ago Eukaryotic cells appear. 1 000 million years ago Multicellular organisms appear.

44. Photosynthesis 3.4 billion years ago First photosynthetic bacteria appeared. They absorbed near-infared instead of visible light and produced sulfur or sulfate compounds instead of oxygen. 2.7 billion years ago Cyanobacteria was the first of the oxygen producers. They used light to produce oxygen.

45. Stable Continents Appear About 2500 million years ago The surface of the Earth was cooled, re-melted, and solidified again. The landmasses would come together and then drift apart again. Plates broke apart and drifted away, forming today’s continents.

46. Ozone Layer About 1600 million years ago The formation of ozone layer starts blocking ultraviolet radiation from the sun. This allowed life to start to appear on the land. The ozone is a form of oxygen.

47. Snowball Earth About 700 million years ago Earth was a planet covered by glacial ice from pole to pole. The temperature would be about -74 degrees. Solar radiation would be reflected back to space by the icy surface. In time, glacial ice would thicken and flow in the opposite direction which would leave sediments behind.

48. Snowball Earth The coldest global climate imaginable - a planet covered by glacial ice from pole to pole. The global mean temperature would be about -50°C (-74°F) because most of the Sun's (Solar) radiation would be reflected back to space by the icy surface. Despite the cold and dry climate, the atmosphere would still transport some water vapor from areas of sublimation (direct change from solid to vapor) to areas of condensation. Given sufficient time, glacial ice would thicken and flow in the opposite direction. Glacial flowage resulted in sedimentary deposits

49. Mass Extinction About 650 million years ago There was a mass extinction of 70% of dominant sea plants. The extinction was caused by global glaciation.

50. First Soft-Bodied Organisms 580 million years ago Soft body organisms started developing These organisms were the jelly fish, tribrachidium, etc.