Teaching about Earth's history is a challenge for all teachers. Time factors of millions and billions of years is difficult even for adults comprehend. However, "relative" dating or time can be an easy concept for students to learn. Once they are able to manipulate the cards into the correct sequence, they are asked to do a similar sequencing activity using fossil pictures printed on "rock layer" cards.
Sequencing the rock layers will show students how paleontologists use fossils to give relative dates to rock strata. Once students begin to grasp "relative" dating, they can extend their knowledge of geologic time by exploring radiometric dating and developing a timeline of Earth's history. These major concepts are part of the Denver Earth Science Project's "Paleontology and Dinosaurs" module written for students daring grades The module is an integrated unit which addresses relative dating of fossils following National Science Education Standards: Fossils indicate that many organisms that lived long ago are extinct.
Extinction of species is common; most of the species that have lived on the earth no longer exist. Fossils provide important evidence of how life and environmental conditions have changed. The complete "Paleontology rrlative Dinosaurs" module takes approximately four weeks to teach. The "Who's On First? Scientific measurements fosxils as radiometric dating use the natural radioactivity of certain elements found in rocks to help determine their age.
Scientists also use relativw evidence from observations of the rock layers themselves to help determine the relative age of rock layers. Specific rock formations are indicative of a particular type of environment existing when the rock was being formed. For example, most limestones represent marine datingg, whereas, sandstones with ripple marks might indicate a shoreline habitat or a riverbed.
Return to top 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, oc 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 fkssils can be worked out. By correlating fossils from various parts of the world, scientists are fossls 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. 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 relative dating of fossils 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: 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 relative dating of fossils rock layer, they are the oldest fossils, or fossils first fossils formed in the past for this sequence of rock layers. Now, look for a card that has either a "T" or "C" written on it. Since this card has relative dating of fossils 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. When you finish, you should have a vertical stack of cards with datiny top card representing the youngest fossils of this rock sequence and the "TC" card at the of the stack representing the oldest fossils. Starting with the top card, the letters should be in order from youngest to oldest. Return to top Procedure Set B: Each card represents a particular rock layer with a collection of fossils that are found in that particular rock stratum.
All of the fossils represented would be found in sedimentary rocks of marine origin. Figure 2-A gives some background information on the individual fossils. The letters on the other cards have no significance to the sequencing procedure and should be ignored at this time. Find a rock layer that has at least one of the fossils you found in the oldest rock layer. This rock layer would be younger as indicated by the appearance of new fossils in the rock stratum. Keep in mind that extinction is forever.
Once an organism disappears from the sequence it cannot reappear later. Use this information to sequence the cards in a vertical stack of fossils in rock strata. Arrange them from oldest to youngest with the oldest layer on the bottom and the youngest on top. This will enable your teacher to quickly check whether you have the correct sequence. Sketches of Marine Fossil Organisms Not to Scale NAME: Three-lobed body; burrowing, crawling, and swimming forms; extinct NAME: Many were large a few rare species were 5 feet in length ; crawling and swimming forms; extinct NAME: