YOU WILL NEED YOUR COMPOSITION BOOK ALL PERIOD TODAY. - Make sure your Origins of Life notes are in your TOC and secured with tape, glue or a staple in your comp book. - Go ahead and put “Fossil Notes” in your TOC, and under that put “Carbon Dating Lab” in your TOC

Today’s Objective (learning goal) To identify how fossils are used as evidence in changes within a species.

Section 14.1 Summary – pages About 95 percent of the species that have existed are EXTINCT—they no longer live on Earth. The oldest rocks that have been found on Earth formed about 3.8 billion years ago. Scientists study fossils to learn about ancient species. Clues to the Past

Section 14.1 Summary – pages Fossils are evidence of organisms that lived long ago that are preserved in Earth’s rocks. TYPES OF FOSSILS Fossils TypesFormation Trace fossils Casts Molds Petrified fossils Amber-Preserved or frozen fossils A trace fossil is any indirect evidence left by an animal and may include a footprint, a trail, or a burrow. When minerals in rocks fill a space left by a decayed organism, they make a replica, or cast, of the organism. A mold forms when an organism is buried in sediment and then decays, leaving an empty space. Petrified-minerals sometimes penetrate and replace the hard parts of an organism At times, an entire organism was quickly trapped in ice or tree sap that hardened into amber.

Section 14.1 Summary – pages Paleontologists, scientists who study ancient life, are like detectives who use fossils to understand events that happened long ago. They use fossils to determine the kinds of organisms that lived during the past and sometimes to learn about their behavior.

Section 14.1 Summary – pages For fossils to form, organisms usually have to be buried in mud, sand, or clay soon after they die. Most fossils are found in sedimentary rocks. These rocks form at relatively low temperatures and pressures that may prevent damage to the organism. Fossils are not usually found in other types of rock because of the ways those rocks form. For example, the conditions under which metamorphic rocks form often destroy any fossils that were in the original sedimentary rock.

Section 14.1 Summary – pages Few organisms become fossilized because, without burial, bacteria and fungi immediately decompose their dead bodies. Occasionally, however, organisms do become fossils in a process that usually takes many years. How fossils form

Section 14.1 Summary – pages A Protoceratops drinking at a river falls into the water and drowns Sediments from upstream rapidly cover the body, slowing its decomposition. Minerals from the sediments seep into the body. Over time, additional layers of sediment compress the sediments around the body, forming rock. Minerals eventually replace all the body’s bone material. Earth movements or erosion may expose the fossil millions of years after it formed.

Section 14.1 Summary – pages Scientists use a variety of methods to determine the age of fossils. Relative dating This method basically indicates that the fossils found closer to the surface are younger, and the fossils found in deeper strata are more primitive (older). (in undisturbed ground) This method does not give a specific age of the fossil or rock.

Section 14.1 Summary – pages Using this principle, scientists can determine relative age and the order of appearance of the species that are preserved as fossils in the layers.

Section 14.1 Summary – pages To find the specific ages of rocks, scientists use absolute dating, also called Radiometric Dating. In this type of dating scientists use radioactive atoms to determine the absolute age of objects.

As specific atoms decay they emit radiation and lose electrons, which causes them to turn into a different element. So- these atoms change from one thing into something else over time- and they do this at a constant rate.

If you know what the unstable atom is (Carbon 14) and you know what it turns into as it decays (Nitrogen 14). And you know the rate at which the unstable atom decays/turns into something else You can measure the amount of the unstable atom in the rock….and compare that to the amount of the new atom This will tell you the age of the sample rock. It takes 5,730 years for ½ of Carbon 14 to turn into Nitrogen 14

Section 14.1 Summary – pages The half-life of a radioactive atom is the time it takes for half of that atom in a sample to decay and turn into another element.

C atoms How many carbon-14 atoms and how many nitrogen-14 atoms will this rock have in 5,730 yrs.

After 5730 years or 1 half-life C and N atoms

After 11,460 yrs or 2 half-lives C and N atoms

After 17,190 yrs or 3 half-lives C and N atoms

After 22,920 yrs or 4 half-lives C and N atoms

After 28,650 yrs or 5 half-lives 8 14 C and N atoms

After 34,380 yrs or 6 half-lives 4 14 C and N atoms

After 40,110 yrs or 7 half-lives 2 14 C and N atoms

Because Carbon 14 has such a short half-life, it can only be used to date things that died recently in geologic history (under 70,000 years ago). If you need to date rocky material from farther back in our geologic past, you must use another method, such as Potassium/Argon, which has a much longer half-life. You can only date organic remains using carbon 14

Some isotopes, however, decay slowly, and several of these are used as geologic clocks. The parent isotopes and corresponding daughter products most commonly used to determine the ages of ancient rocks are listed below: Most radioactive isotopes have rapid rates of decay (that is, short half-lives) and lose their radioactivity within a few days or years. Parent Isotope Stable Daughter Product Currently Accepted Half-Life Values Uranium-238Lead billion years Uranium-235Lead million years Thorium-232Lead billion years Rubidium-87Strontium billion years Potassium-40Argon billion years Samarium-147Neodymium billion years

Section 1 Check Question 1 D. land plants C. reptiles B. mammals According to fossil record what organisms have occupied Earth for the longest period of time? A. prokaryotes

Section 1 Check The answer is A. Single-celled prokaryotes have been present on the Earth since the Precambrian period and are still present today.

Section 1 Check Question 2 Given that volcanoes have erupted since Earth’s early history, why does volcanic rock not contain many fossils? Answer Lava is subject to high heat and strong pressure changes that prevent fossils from forming in it.

1. Secure your Fossil Notes into your Comp Book on the appropriate page. 2. Once you have that done, turn to the next page and write “Carbon Dating Lab” as your title. 3. Write “Purpose” and copy the purpose down underneath the title. Carbon Dating Lab Purpose: to simulate how radioactive isotopes decay over time in rock, and how scientists are able to age them based on this fact.

4. Next….write “Pre-Lab Questions” under your purpose. 5. Write the questions below and COMPLETE answer. Pre Lab Questions: 1. How do scientists use radioactive isotopes to determine the age of rocks and fossils? 2. What does Carbon 14 turn into as it decays? 3. Explain the “half-life” of an atom.