How do we date rocks? A geologist explains!
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- čas přidán 5. 09. 2024
- Secrets of Geology Episode 3: Dating in Deep Time
#geology #time #dating
Dating in Deep Time: How do we know how old rocks and fossils are? It's not like they have a time stamp, right?! Turns out they do...sorta, and I'm going to explain how they work and how we read them!
Special thanks to Dr Jen Fehrenbacher @DeepSeaDrifter on twiter and t.co/gN4KzD97u... for her blog
Alison Troup @havecamerawillsnap on instagram
and Sophie Alexander @SophiMAlexander on twiter for the microflora photos.
Thanks also to Prof Conall Mac Niocal @conall_macn on twitter and 'Mysterious' Dr Ken Amor (too mysterious for social media) for lab access.
More cool geology on my socials!
Twitter @geology_johnson / @Evidently_Sci
Insta @geology_johnson
Facebook @idigfossils
Blog1 / geologyjohnson
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I did A-level Geology in 1981-82. Now I'm retired, getting out and examining the geological landscape as an amateur has become a fun hobby and like a giant cryptic puzzle.
yup, a puzzle thousands of kilometers across and billions of years old, plenty to keep us entertained for our whole lives! If you fancied doing a degree, then many retired folks do the geology degree at birkbeck college, university of london, which I did. you can do it part time and online too (like me!) and even break it down into module based certificates that build up into a degree. :)
Thank you for the clear explanation! Im no scientist but a visual artist. This information gives me a solid base to my artworks. I love to depict passing time, layers and conneting pieces of the world. Will be learning more 😊, thank you!
Sounds fun, glad you enjoyed the videos.
How do we know the sand on top is older than the sand below? Couldn’t the top sand have just eroded more recently from an equal age or older rock than the sand below?
There are surface processes like you describe that can mix the layers up a little bit. We have to be careful and make sure we look for the clues that indicate the processes have occurred.
However, sand is loose sediment, where as sandstone is sand that has undergone chemical and physical processes that turn it into a solid rock. So the solid rock is less prone to the kind of reworking you mention. The last thing is that when you are working on million or billion year timescales, the small scale differences caused by those reworking processes get averaged out.
Fascinating! Thank you!
Glad you enjoyed it, hope it's useful!
I have a question.
Where does the dating of organisms come from? I know we have absolute dating. But really old absolute dating (uranium) can only be preformed on rocks with Zircon.
So are rocks with Zircon plentiful enough and found near fossils that we can be confident in the age of the fossils. or do we find Zircon in a Strata and date all other strata and fossils by that single source of zircon?
Good question. There are a bunch of minerals we can date, including things like the phosphate and carbonate in shells and bones. For dating fossils we use creatures that are really common and found all over the world for that time period. We call these index fossils. Because they are so wide spread, they are usually some that are near things like volcanic ash or lava that has datable minerals in. We can also use detrital minerals like zircons to get relative ages too. It's like a detective story where you have to take lots of different lines of evidence to get an answer.
I have a question I am trying to figure out. How old is liquid lava and can it be dated?
When we date rocks like lava, we are dating the age at which the mineral crystalized. So liquid lava has an age of zero until it crystallises. Some times lava is carrying crystals that formed in previous melt stages so we can date those and this helps us understand how the lava is moving through the crust.
We date the minerals using the decay of radioactive elements trapped in the mineral. A common example is uranium in zircons. The zircon crystal structure cannot include lead when it crystalises, but it can include uranium. Over time the uranium decays into lead so we are able to measure how much lead and uranium is present in the crystal and this gives us an age.
@@geologyjohnson7700 Thst is a bit confusing that it goes back to zero. It sort of seems like we truly cannot know the age of rocks any more than we can know the age of water since it is in a constant state of change.
Everything is as old as the very beginning it seems which tells me this could not have happened by chance.
@@DestinyLabMusic When I say reset to zero, I mean reset to the date of the crystalisation. The thing to remember, is that you are not dating the lava, just the crystalisation date of specific minerals in the lava. The lava formed from the melting of a pre-existing rock which had it's own age. When that rock and all the minerals in it melt, that date gets reset to the new date when the lava recrystalises. We know it's accurate because it lines up with all the other evidence we have for the age of rocks and the Earth.
The other thing to remember is that lava that has erupted is now seperate from the mantle where it was generated. That's why it has a seperate recrystalisation age. It's now seperate from the source of radioactive elements in the mantle that have been there since the earth formed. Thats also why we can date the water in ice cores and in sealed caves, etc, because they are now seperate from the ocean where the values of the isotopes are homogenised.
@@geologyjohnson7700 The thing is that I do not think that most people know this is how we date rocks.
Geologists speak as if these are literal ages. Most people that I have talk to you about the dating of rocks, seem to think that we have it down to a complete science and we know exactly the literal ages of rocks, and not just the layer it is found or when it’s solidified from lava.
After much investigation I think that many teachings on evolution and the age of the earth are not true.
It seems circular reasoning because when I ask a geologist, how we date rocks, they say it’s by the fossils that surround it, and when I ask an archaeologist how we date fossils, they say it’s by the rock layer they are found in.
@@DestinyLabMusic seems kinda suspicious if you ask me
Nice vid:) You could do with being a bit louder and crisper though. Better mic?
My wee camera does not take a mic so I'm a bit restricted atm. Looking into alternative options though! ☺️
Fairy snuff:) (fair enough)
How do we measure the half life of a rock?
Rocks themselves don't really have half lives. "half life" refers to the amount of time it takes for half of a quantity of a radioactive element to decay into a new isotope or element. Is this what you mean? If so, we either grind the rock to a powder, dissolve it in acid, then put the liquid through a machine called a mass spectrometer. This gives us a "bulk rock" measurement for the age. If we want to measure the age of a specific mineral in the rock, then we break the rock up, extract those minerals, then dissolve them and put them through the mass spec the same way. This gives us the age of that specific mineral.
I'll do a viewer Q and A video and give more info about how the mass spec works in that cos it's easier with pictures. :)
Does he ever have a problem with the Christian fundamentalists?
That's a whole different bunch there all together. I mean this in a good way. We Christians are variably different as it is and these geologists are not too worried about God first or His word or rely on the resurrection of Jesus and His saving sacerfice BUT they ARE focused on rocks, natural phenomenon that can alter them or their birth/rebirth (crystallization). I'm not a geologist by any means so I probably slaughtered that description but I hope you see what I mean. Geology is not focused on morals or those kind of truths or ways to live/walk but instead search history with rocks or other information of the previous environment it came from.
Depends how you mean "problem".
If you are asking if I dislike religious people, then the answer is no, I do not dislike religious people in general. I have friends and colleagues from several different religions including christianity.
If you mean, do christian, or other religious fundamentalists cause me problems, again, the answer is no. In the UK and western Europe, young Earth creationist beliefs not widespread and mainstream the way they are in e.g. the USA.
Occasionally religious people from overseas will send us emails or letters about young Earth creationism. They are always very polite and say they are worried for our souls.
However, I have had rude and abusive interactions with various conspiracy followers such as flat earthers, hollow earthers, ancient aliens, and ancient technology hypothesists.