UCMP geologic timeline - includes links to find out more about the eras, periods, Earth Science Lab Relative Dating #2 - You can enter the order you think Start studying Earth science Lab (geologic time lab). Learn vocabulary, terms Relative dating. CLICK THE CARD TO . Geologic time scale. Eon Era Period. Absolute dating is exemplified by when you give your age, but relative dating is The calendar of earth history is called the GEOLOGIC TIME SCALE. For the laboratory, you will NOT need to know the geologic time scale; however, it is.
Fault displacing strata Is the fault younger or older than the strata? Geologic events are arranged in Geologic events are arranged in chronological sequences using relative dating chronological sequences using relative dating principles which came first? No numerical values are applied. Radioactive isotopes unstable elements decay Radioactive isotopes unstable elements decay into stable atoms rate of decay is measureable into stable atoms rate of decay is measureable with a numerical value with a numerical value An actual number numerical age can be An actual number numerical age can be applied.
I will get an A on my exams and quizzes. Describe the difference between: Relative Dating techniques Absolute Dating techniques 2. What role does uniformatarianism play when interpreting the previous field trip when interpreting the previous field trip slides? All strata is datable. Layers of strata that formed in the past are subject to erosive forces. Earthquake faults displacing strata are always older than the displaced strata.
Observing geological processes today, ensures the accuracy of dating a sequence of strata that has formed accuracy of dating a sequence of strata that has formed in the geological past. Nicholas Steno — proposed the following relative dating principles: The Principle of Original Horizontality: Sedimentary rock layers are deposited as horizontal strata.
Any observed non-horizontal strata have been disturbed. The Principle of Superposition In any undisturbed sequence of strata, the oldest stratum is at the bottom of the sequence, and the youngest stratum is on top. Any geologic feature that cuts across another geologic feature is younger. Unit 5 or Unit 6? Which is older, the fault or volcanic layer? Volcanic layer fault Which is younger, the dike or country rock?
Which is younger, the dike or country rock? Can you identify the inclusions found in this Sierra Nevada Mountain batholitic material? Older Younger 21 II this geology class. Explain the concept of relative dating. Draw a diagram, and explain each of the following dating principles: Units B and C because of original horizontality B.
Units E and F because of cross-cutting relations C. Units E and F because of inclusions principle D. Units B and A because of cross-cutting relations A. Units B and A because of cross-cutting relations 23 Ok — given the principles, what is wrong with this stratigraphic section? Active erosional processes shaping the surface A period of erosion creating the unconformity Continued deposition burying the erosional surface to create an angular unconformity 27 Grand Canyon Stratigraphy Types of Unconformities 28 II this geology class.
I will get an A on my exams and quizzes 5. Describe an unconformity and what what it represents regarding geologic what it represents regarding geologic history. Most organisms composed of soft parts. On other solid-surfaced worlds -- which I'll call "planets" for brevity, even though I'm including moons and asteroids -- we haven't yet found a single fossil.
Something else must serve to establish a relative time sequence. That something else is impact craters. Earth is an unusual planet in that it doesn't have very many impact craters -- they've mostly been obliterated by active geology.
Relative Dating Lab
Venus, Io, Europa, Titan, and Triton have a similar problem. On almost all the other solid-surfaced planets in the solar system, impact craters are everywhere. The Moon, in particular, is saturated with them.
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We use craters to establish relative age dates in two ways. If an impact event was large enough, its effects were global in reach. For example, the Imbrium impact basin on the Moon spread ejecta all over the place. Any surface that has Imbrium ejecta lying on top of it is older than Imbrium.
Any craters or lava flows that happened inside the Imbrium basin or on top of Imbrium ejecta are younger than Imbrium. Imbrium is therefore a stratigraphic marker -- something we can use to divide the chronostratigraphic history of the Moon. Apollo 15 site is inside the unit and the Apollo 17 landing site is just outside the boundary. There are some uncertainties in the positions of the boundaries of the units. The other way we use craters to age-date surfaces is simply to count the craters.
At its simplest, surfaces with more craters have been exposed to space for longer, so are older, than surfaces with fewer craters. Of course the real world is never quite so simple. There are several different ways to destroy smaller craters while preserving larger craters, for example.Geologic Time Scale
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.
Relative and absolute ages in the histories of Earth and the Moon: The Geologic Time Scale
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.
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.
The Geologic Time and Dating
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. 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. We have a lot of rock samples and a lot of derived ages, but it's hard to be certain where a particular chunk of rock picked up by an astronaut originated.
The Moon's surface has been so extensively "gardened" over time by smaller impacts that there was no intact bedrock available to the Apollo astronauts to sample. And it's impossible to know where a lunar meteorite originated. So we can get incredibly precise dates on the ages of these rocks, but can't really know for sure what we're dating.
Consequently, there is a lot of uncertainty about the ages of even the biggest events in the Moon's history, like the Nectarian impact. There's some evidence suggesting that it's barely older than Imbrium, which means that there was a period of incredibly intense asteroid impacts -- the Late Heavy Bombardment.