DETERMINING AGE OF ROCKS AND FOSSILS
This would also mean that fossils found in the deepest layer of rocks in an on geological events (sea encroachments, mountain-building, and depositional. I. Introduction & Purpose: The purpose of this lab is to learn and apply the concepts of relative and absolute dating to rocks, fossils and geologic events. -Lab: Relative Dating- Name______________ The process of showing that rocks or geologic events occurring at different Index fossils and similar rocks types help geologists establish correlations between distance rock outcrops.
This particular form isotope of lead is called Pb U is the parent isotope of Pb, which is the daughter isotope.Relative Dating - Example 2
Many rocks contain small amounts of unstable isotopes and the daughter isotopes into which they decay. Where the amounts of parent and daughter isotopes can be accurately measured, the ratio can be used to determine how old the rock is, as shown in the following activities. That chance of decay is very small, but it is always present and it never changes. In other words, the nuclei do not "wear out" or get "tired".
If the nucleus has not yet decayed, there is always that same, slight chance that it will change in the near future. Atomic nuclei are held together by an attraction between the large nuclear particles protons and neutrons that is known as the "strong nuclear force", which must exceed the electrostatic repulsion between the protons within the nucleus.
In general, with the exception of the single proton that constitutes the nucleus of the most abundant isotope of hydrogen, the number of neutrons must at least equal the number of protons in an atomic nucleus, because electrostatic repulsion prohibits denser packing of protons. But if there are too many neutrons, the nucleus is potentially unstable and decay may be triggered.
This happens at any time when addition of the fleeting "weak nuclear force" to the ever-present electrostatic repulsion exceeds the binding energy required to hold the nucleus together. In other words, during million years, half the U atoms that existed at the beginning of that time will decay to Pb This is known as the half life of U- Many elements have some isotopes that are unstable, essentially because they have too many neutrons to be balanced by the number of protons in the nucleus.
Each of these unstable isotopes has its own characteristic half life. Some half lives are several billion years long, and others are as short as a ten-thousandth of a second. On a piece of notebook paper, each piece should be placed with the printed M facing down.
Dating of rocks fossils and geologic events lab answers
This represents the parent isotope. The candy should be poured into a container large enough for them to bounce around freely, it should be shaken thoroughly, then poured back onto the paper so that it is spread out instead of making a pile. This first time of shaking represents one half life, and all those pieces of candy that have the printed M facing up represent a change to the daughter isotope. Then, count the number of pieces of candy left with the M facing down.
These are the parent isotope that did not change during the first half life. The teacher should have each team report how many pieces of parent isotope remain, and the first row of the decay table Figure 2 should be filled in and the average number calculated. The same procedure of shaking, counting the "survivors", and filling in the next row on the decay table should be done seven or eight more times.
Each time represents a half life. Each team should plot on a graph Figure 3 the number of pieces of candy remaining after each of their "shakes" and connect each successive point on the graph with a light line.
AND, on the same graph, each group should plot points where, after each "shake" the starting number is divided by exactly two and connect these points by a differently colored line. After the graphs are plotted, the teacher should guide the class into thinking about: Is it the single group's results, or is it the line based on the class average?
U is found in most igneous rocks.
Unless the rock is heated to a very high temperature, both the U and its daughter Pb remain in the rock. A geologist can compare the proportion of U atoms to Pb produced from it and determine the age of the rock. The next part of this exercise shows how this is done.
Each team is given a piece of paper marked TIME, on which is written either 2, 4, 6, 8, or 10 minutes.
The team should place each marked piece so that "U" is showing. This represents Uranium, which emits a series of particles from the nucleus as it decays to Lead Pb- When each team is ready with the pieces all showing "U", a timed two-minute interval should start.
Le coin du Pecheur
During that time each team turns over half of the U pieces so that they now show Pb This represents one "half-life" of U, which is the time for half the nuclei to change from the parent U to the daughter Pb The study and comparison of exposed rock layers or strata in various parts of the earth led scientists in the early 19th century to propose that the rock layers could be correlated from place to place.
Locally, physical characteristics of rocks can be compared and correlated.
On a larger scale, even between continents, fossil evidence can help in correlating rock layers. The Law of Superposition, which states that in an undisturbed horizontal sequence of rocks, the oldest rock layers will be on the bottom, with successively younger rocks on top of these, helps geologists correlate rock layers around the world. This also means that fossils found in the lowest levels in a sequence of layered rocks represent the oldest record of life there.
By matching partial sequences, the truly oldest layers with fossils can be worked out. By correlating fossils from various parts of the world, scientists are able to give relative ages to particular strata. This is called relative dating. Relative dating tells scientists if a rock layer is "older" or "younger" than another. This would also mean that fossils found in the deepest layer of rocks in an area would represent the oldest forms of life in that particular rock formation.
WHO'S ON FIRST? A RELATIVE DATING ACTIVITY
In reading earth history, these layers would be "read" from bottom to top or oldest to most recent. If certain fossils are typically found only in a particular rock unit and are found in many places worldwide, they may be useful as index or guide fossils in determining the age of undated strata.
By using this information from rock formations in various parts of the world and correlating the studies, scientists have been able to establish the geologic time scale. This relative time scale divides the vast amount of earth history into various sections based on geological events sea encroachments, mountain-building, and depositional eventsand notable biological events appearance, relative abundance, or extinction of certain life forms.
When you complete this activity, you will be able to: Explore this link for additional information on the topics covered in this lesson: The nonsense syllables or letters sometimes overlap other cards and are being used to introduce the students to the concept of sequencing. The cards should be duplicated, laminated, and cut into sets and randomly mixed when given to the students.
It is recommended that students complete Procedure Set A and answer the associated Interpretation Questions correctly before proceeding to Set B. The cards in Set B represent rock layers containing various fossils. For Set Byou may want to color code each organism type i. Sequencing the rock layers will show the students how paleontologists use fossils to give relative dates to rock strata.
Return to top To enhance this activity, have students match the fossil sketches to real fossils. The following is a list of fossils in the John Hanley Fossil Teaching Set that may be useful in this activity.
It may be useful to share with students after they have completed Set B and answered the Interpretation Questions. The first card in the sequence has "Card 1, Set A" in the lower left-hand corner and represents the bottom of the sequence. If the letters "T" and "C" represent fossils in the oldest rock layer, they are the oldest fossils, or the first fossils formed in the past for this sequence of rock layers.
Since this card has a common letter with the first card, it must go on top of the "TC" card. The fossils represented by the letters on this card are "younger" than the "T" or "C" fossils on the "TC" card which represents fossils in the oldest rock layer. Sequence the remaining cards by using the same process.