Describe how relative dating methods allowed the geologic time scale to be Most of the processes that shape Earth operate extremely slowly – in vast. The discovery of radioactivity and its application to dating rocks is perhaps one to date the rocks and consequently change the "relative" geologic time scale Activity 8 is taken from Investigating Earth: A Geology Laboratory Text () by. The Geologic Time Scale – “The Earth's history book” Let's take a field trip and Relative Dating Techniques: Geologic events are arranged in Geologic events.
Relative Dating Lab
Explain the law of fossil succession and how this law allows dating of strata. How has fossil succession helped geologists unravel earth history? Fossils discovered in lower sections of rock layers are younger than fossils above.
Most fossil soft parts are preserved. The age of fossils is marked by the preservation of all hard parts.
The Geologic Time and Dating
Fossils can be dated by using the principle of superposition. The principle of fossil succession states: Radiometric dating — applying a number radioactive atoms isotopes decay at a constant rate over time Review of the atom: U Pb Decays 37 Isotopes decay at a fixed rate. Decay rate is measureable. Isotope decay is not influenced by weathering. One isotope will decay into another isotope.
Radio active decay U Pb Alpha emission Mass reduced by 4 Atomic reduced by 2 Beta emission Mass remains unchanged Atomic increases by 1 38 How does radiometric dating work, and where does the age number come from?
Define the following absolute dating terms: Explain how the half-life is used to calculate an absolute age. If the half-live for decay is 2. Earth believed to be 4. The Geologic Time Scale: It combines both relative and absolute dating.
How accurate is the Geologic Time Scale? You should be able to draw the Geologic Time Scale and label it with the following: Time Scale and label it with the following: List major characteristics of each period. An earlier current-formed ripple set at bottom of slide was later modified by a second ripple train migrating at right angles to the first.
Crests of the first set are preserved in the troughs of the second set, hence, the ladderback appearance. Similar ripples occur in tidal environments and correct interpretation requires that the local facies content be taken into account. Resources Before you begin this activity, read the book chapter listed below, which is available online through Library Reserves.
Electronic course reserves, or "e-Reserves," are articles and book chapters that are available online through the University Libraries. Access this lesson's reading by clicking on the Library Resources in Canvas, then clicking on the "E-Reserves" link. There are several different ways to destroy smaller craters while preserving larger craters, for example. Despite problems, the method works really, really well. Most often, the events that we are age-dating on planets are related to impacts or volcanism.
Volcanoes can spew out large lava deposits that cover up old cratered surfaces, obliterating the cratering record and resetting the crater-age clock. When lava flows overlap, it's not too hard to use the law of superposition to tell which one is older and which one is younger. If they don't overlap, we can use crater counting to figure out which one is older and which one is younger. In this way we can determine relative ages for things that are far away from each other on a planet.
Interleaved impact cratering and volcanic eruption events have been used to establish a relative time scale for the Moon, with names for periods and epochs, just as fossils have been used to establish a relative time scale for Earth. The chapter draws on five decades of work going right back to the origins of planetary geology. The Moon's history is divided into pre-Nectarian, Nectarian, Imbrian, Eratosthenian, and Copernican periods from oldest to youngest.
The oldest couple of chronostratigraphic boundaries are defined according to when two of the Moon's larger impact basins formed: There were many impacts before Nectaris, in the pre-Nectarian period including 30 major impact basinsand there were many more that formed in the Nectarian period, the time between Nectaris and Imbrium. The Orientale impact happened shortly after the Imbrium impact, and that was pretty much it for major basin-forming impacts on the Moon.
I talked about all of these basins in my previous blog post. Courtesy Paul Spudis The Moon's major impact basins A map of the major lunar impact basins on the nearside left and farside right.
There was some volcanism happening during the Nectarian and early Imbrian period, but it really got going after Orientale.
Vast quantities of lava erupted onto the Moon's nearside, filling many of the older basins with dark flows. So the Imbrian period is divided into the Early Imbrian epoch -- when Imbrium and Orientale formed -- and the Late Imbrian epoch -- when most mare volcanism happened. People have done a lot of work on crater counts of mare basalts, establishing a very good relative time sequence for when each eruption happened. The basalt has fewer, smaller craters than the adjacent highlands.
Even though it is far away from the nearside basalts, geologists can use crater statistics to determine whether it erupted before, concurrently with, or after nearside maria did. Over time, mare volcanism waned, and the Moon entered a period called the Eratosthenian -- but where exactly this happened in the record is a little fuzzy. Tanaka and Hartmann lament that Eratosthenes impact did not have widespread-enough effects to allow global relative age dating -- but neither did any other crater; there are no big impacts to use to date this time period.Geologic Time Scale
Tanaka and Hartmann suggest that the decline in mare volcanism -- and whatever impact crater density is associated with the last gasps of mare volcanism -- would be a better marker than any one impact crater. Most recently, a few late impact craters, including Copernicus, spread bright rays across the lunar nearside.
Presumably older impact craters made pretty rays too, but those rays have faded with time. Rayed craters provide another convenient chronostratigraphic marker and therefore the boundary between the Eratosthenian and Copernican eras.
The Copernican period is the most recent one; Copernican-age craters have visible rays. The Eratosthenian period is older than the Copernican; its craters do not have visible rays. Here is a graphic showing the chronostratigraphy for the Moon -- our story for how the Moon changed over geologic time, put in graphic form. Basins and craters dominate the early history of the Moon, followed by mare volcanism and fewer craters.
Red marks individual impact basins. The brown splotch denotes ebbing and flowing of mare volcanism. Can we put absolute ages on this time scale? Well, we can certainly try.
The Moon is the one planet other than Earth for which we have rocks that were picked up in known locations. We also have several lunar meteorites to play with. Most moon rocks are very old. All the Apollo missions brought back samples of rocks that were produced or affected by the Imbrium impact, so we can confidently date the Imbrium impact to about 3.
And we can pretty confidently date mare volcanism for each of the Apollo and Luna landing sites -- that was happening around 3. Not quite as old, but still pretty old.
Geologic Time Deciphering Earth History and Time Scale.
Alan Shepard checks out a boulder Astronaut Alan B. Note the lunar dust clinging to Shepard's space suit. The Apollo 14 mission visited the Fra Mauro formation, thought to be ejecta from the Imbrium impact.
Beyond that, the work to pin numbers on specific events gets much harder. There is an enormous body of science on the age-dating of Apollo samples and Moon-derived asteroids.