Question

In which geologic era are we?


A.


Precambrian


B.


Cenozoic


C.


Mesozoic


D.


Paleozoic

Answer 1

@EclipsedStar

Answer 2

We are in the Cenezoic Era! :o)

Answer 3

Here is a map>>> http://www.exploratorium.edu/evidence/images/geomap-chart-english.jpg

Answer 4

You would be best served learning mnemonics to remember all these eras, periods, etc.
This may also help!
http://science.sbcc.edu/~earthsc/geo/TimeScaleMnemonics.htm

Good luck! :o)

Answer 5

If layer G formed just after the dinosaurs became extinct, then when was layer F formed?




A.


Precambrian era


B.


Cenozoic era


C.


Paleozoic era


D.


Mesozoic era

Answer 6

@ariel28
Hopefully you have read your textbook and understand "The law of original horizontality". This is a fancy way to say that all layers or sedimentary rock are laid down in horizontal bands. Then, they of course can be shifted around, eroded, uplifted, or downshifted due to tectonic forces.

In your map you provided, B was deposited first, then C after that, then D, E, F (assuming of course all those layers were not completely overturned be some seriously strong tectonic forces) but that doesn't happen very often, so assume the order of deposition from first to last is B,C,D,E,F...now we will stop at layer F for a second to talk about what has happened...

You can see that after layer F was deposited, that some tectonic uplifting occurred and pushed up the right side of the geologic sequence so then everything got tilted...then you can probably imagine that those sideways layers got eroded a bit...then after the erosion stopped, new layers started getting deposited on top of F, specifically layer G was deposited, then layers H, and then finally layer I...so the newest layer is "i", the oldest is "B"...

so now that we have a good conceptual view of what happened as the geologic sequence was laid down, your question was:

If layer G formed just after the dinosaurs became extinct, then when was layer F formed?

To answer this question, you obviously first have to know when the dinosaurs became extinct...Hopefully you read about this but the best evidence is due to a huge asteroid striking the Earth near the Yucatan Peninsula about 65 million years ago and sending up a mind boggling amount of dust into the air, blocking out the sun and killing most surface life on the planet at that time!

As a result of all this dust being in the air, it eventually settled back down to the ground in a "horizontal layer" all over the entire Earth. What's interesting about this layer of asteroid blown dust is that virtually anywhere in the world you go, you can dig down and find this layer of dirt, the very stuff that blocked out the sun and killed the dinosaurs. This layer used to be called the K-T Boundary, which stood for the boundary layer between the Cretaceous and Tertiary Periods, essentially, this K-T Boundary, now called K-Pg Boundary for Cretaceous-Paleogene Boundary, marked the "END OF THE CRETACEOUS ERA"...

So, remember to refer to your geologic time scale map>>> http://www.exploratorium.edu/evidence/images/geomap-chart-english.jpg

If layer G formed just after the dinosaurs became extinct, that would have to mean that Layer G formed "after" the Mesozoic Era, or stated another way, since the dinos were dead and then Layer G formed, then Layer G would have been deposited in the Cenozoic Era!

So when was Layer F deposited then?
Well the best answer would be at "sometime while the dinos were still alive or before".

So go through your choices and think about it.

Could it have been deposited in the Pre-cambrian? Possibly but since that was literally billions of years ago instead of hundreds of millions, there would have to have been many more layers on top of F that were deposited and then eroded to erase all the layers that would be missing between billions of years ago and the time when the dinos were gone. Now your sequence map does in fact show erosion prior to G being laid down, the only way you could truly eliminate Layer F as being laid down in the Pre-cambrian would be to isotopic dating on a sample of F. but since barely any Precambrian rock still exists this probably isn't the best answer they were looking for but you could argue that the way they asked the question, there isn't enough data to answer definitively. But since they aren't thinking that deeply, they probably want you to pick some Era closer in time to when Layer G was depoisted.

Could it have been deposited in the Paleozoic Era? Yes it could have because of the the same reason I gave above, but since rock layers are usualy laid down with only millions of years or less between them, the Paleozoic would have been a very long time ago, so they probably don't want this answer, but again you could argue that there isn't enough data without iostopic dating to be certain.

The best answer is probably the Mesozoic era, because it is technically just before the dinos died and just before Layer G was deposited.

I hope all this helps you but you should discuss the validity of the question with your professor because it is really a dumb question without them being more specific but for the sake of them asking dumb questions, I would choose Mesozoic Era.

Hope this helps! :o)

Answer 7

Just one correction above, I meant to say Cenozoic Period, not Era. :o)

Answer 8

1 is C