Magandang araw sa inyong lahat. Sa araw na ito, pag-uusapan natin ang Relative and Absolute Dating. Masasagot natin ang tanong na How do geologists determine the age of stratified rocks?
Nung nakaraan, kung maaalala ninyo, napag-usapan natin ang layers of rocks and correlation of rocks. In correlating rocks, geologists are able to identify kung aling layer yung mas matanda. or aling layer yung mas mata.
With that, nakocorrelate yung edad ng formation ng rocks. However, hindi nito na bibigay sa mga geologist yung exact age kung kailan nabuo itong layers of rocks na ito. And remember, some fossils are found in these layers.
So, may effect din yun in determining the age of rocks. So, pag sinabi natin relative age, It refers to the order in which the events occurred. It does not give you the exact date or exact years or exact numbers. Pero it will describe to you alin ang nauna at alin ang sumunod. But not the numbers.
Pag naman absolute age of rocks, it gives you a number that will describe Kailan nangyari ang event na ito? In addition to relative age, Geologists use field observations to determine relative ages. So ano yung field observation na yan? So yan yung pagtingin ng mga layers of sediment rocks na na-deposit into different locations or areas. So they determine which layer of rock is younger or older.
So ang pag-determine ng... Layer of rock kung sino ang mas mata or ano yung mas matanda is called relative dating. And the age is called relative age. If we could also remember...
These laws or principles are being used to determine the relative age of rocks or rock layers. So, first is the original horizontality principle. So, maalala natin that Sediments are deposited in flat layers.
So yun yung sinasabi sa original horizontality. So yung mga sediments na yan, they are deposited in flat surface or surfaces. Pag superposition naman, or principle of superposition, kung alin yung nasa ilalim ay siyang mas matanda, at kung ano yung nasa mas mataas na layer ay siyang mas bata.
Sa principle of crosscutting, Nagkakaroon ng magma-intrusion which serves as the younger layer or dahil sa fault, nagkakaroon ng space at may mga nadedeposit doon na rocks. So yun yung mas younger and the other of course are older than this part. So sa principle of funnel succession, it... Has the fossils found in rocks?
At pag may presence ng fossils, geologists will be able to determine which period in the Earth's history na buo itong layer na ito. because of this fossilized organism. Dahil may mga fossils na nabuhay on a certain period in the Earth's history, malalaman nila kung anong era nabuo itong layer na ito.
Ano naman yung principle of lateral continuity? So makikita natin that There is break or there is this area na hindi conform doon sa layers na meron sa second, third, and fourth. What does that mean?
Ibig sabihin ba nandiyan na talaga siya? Kasi nagde-deposit naman yung layers. The answer is no. Scientists or geologists will assume that this layer is continuous to this area. So ina-assume nila na itong layer ng rock na ito ay continued dito.
Same as true with this. Same as true with this. Possibly, nagkaroon ng erosion or changes with the geologic forces that change this area.
But definitely, with the principle of lateral continuity, ang mga layers na iyan ay continuous. So ginagamit ang mga principles na yun para malaman kung aling rocks ang mas bata at aling layers of rocks ang mas matanda. So ang tawag doon ay relative dating.
Because of the information and technological advancements that we have right now, geologists can now determine the absolute age of rocks, rock layers, and fossils. This process is called absolute dating or absolute age. or radiometric dating. So, dinedetermine dito yung absolute age ng materials at gumagamit sila ng radioactive decay information na nakuha nila within the rocks. So, ano itong...
process na ito. So, radioactive decay happens when unstable isotopes or elements decompose spontaneously. So, para lang mabigyan ng information sa isotopes, paliwanag muna natin ang ibig sabihin ng isotopes. Isotopes are atoms of the same element but with different number of neutrons. So ano yung same elements?
So they must have the same number. of proton or the positively charged particle in the nucleus of the atom. The number of protons of the atom determines the identity of the element. Let's say, pag may isang proton, that's hydrogen. Pag may dalawang proton, hindi na siya hydrogen.
Helium na siya. Pag may tatlong proton, hindi siya hydrogen, hindi siya helium, lithium na siya. And so on and so forth.
So kung familiar tayo sa periodic table of elements, the atomic number represents their identity. Because the atomic number is representing the number of proton of the element. So nabanggit ko kanina that So, Proton 1 or elements with one proton only are hydrogen. At sa case natin, meron tayong tatlong isotopes or kind or variation of the element.
hydrogen. Protium, deuterium, tritium. So lahat sila ay hydrogen. Why? Lahat sila ay may isang proton.
So all of them are hydrogen. Variation lang sila. So isotopes are variation of the same elements.
So ano pa yung description ng isotopes? They have different number of neutrons. Yung protium, which is the hydrogen with one proton, does not have neutron.
Ang deuterium naman may isang neutron. Ang tritium naman may dalawang neutron. So lahat sila ay hydrogen. Pero iba yung identity nila dahil sa presence and absence and difference in number of neutron. So anong behavior?
This one is stable. Meaning to say, it will not emit radioactive particle or it will not decay spontaneously kasi stable siya. Unlike the other types of... isotopes that are not stable which means they will release radioactive particles or radiation for them to become stable. So, yun yung tinatawag na radioactive decay.
Another example of isotope is carbon. So we are familiar with carbon na nasa periodic table at ang kanyang mass number kung familiar kayo is 12 at siya ay stable. But there is another type of carbon that exists in the universe which has a mass number of 14. Saan galing yung 14? Plus na protons and neutrons. So it represents the mass of the element or the isotope.
So this one is stable. This one is not stable. So what will be the behavior of this carbon-14?
It will release radioactive particles to become stable. So that is radioactive decay. Another concept that geologists use to determine In the absolute age of rocks is half-life. So ano naman yung half-life?
This is the time taken for the radioactive particles to become half of its original value. So, mangangalahati daw ang isang specific isotopes for a certain period of time. For example, These are some examples of radioactive isotopes.
So we have carbon-14, potassium-40, uranium-238, and rubidium-87. Carbon-14 has a half-life of 5,700 years. What does that mean? Kung meron tayong certain amount of Carbon-14, it will retain its amount. Until maritch yung 500, 7,000 years kung saan, madidisintegrate na siya into half of its value.
So this half-life is a natural process and these numbers are fixed, meaning to say it does not change. So every 5,700 years, a certain amount of carbon will turn into half of its value. For potassium-40, its half-life is 1,300,000,000 years. Uranium-238 has a half-life of 4.5 billion years. Rubidium-87 has a half-life of 49 billion years.
So, saan ginagamit itong half-life na ito in terms of absolute dating? So, they measure the amount of the radioactive isotopes present in a rock or in a layer of rock and compare to what we call the daughter material. So, ano naman itong daughter material na ito? So the daughter material is the stable element which came from the parent material.
So ano yung parent material? Siya yung unstable isotope. Siya yung radioactive. Siya yung nagre-release ng radioactive particles.
Siya yung mag-a-undergo ng continuous disintegration para maging stable. So sa example natin, Carbon-14 is the parent material. And this arrow represents the radioactive disintegration.
And it will turn to a more stable isotope na nitrogen-14. Same as true with the other examples here. Like uranium-238, so it will continuously emit radioactive particles up until maritch niya yung stable isotope na lead-206.
Let's say we have carbon-14 as an example, para lang mas ma-illustrate natin yung idea about half-life. Carbon-14 is present among animals or living organisms. When animals die, itong carbon-14 will be released.
So during death, Yung amount of carbon-14 is intact, 100% pa. Now, sabi natin that the half-life of carbon-14 is 5,700 years. So, from its death or the death of the animals or after release of carbon-14, and the first 5,700 years happen, the amount or the original amount will turn into half. what will happen to the other half?
Magiging daughter material. So, magiging stable na siya in that case. Another 5,700 years have passed, the 50% will then again turn into half, which is 25%, at ma-add up yung nawalang 25% sa kanya to the daughter material.
So what's the trend? As time passes by, the parent material, to become stable, is... decreasing its amount.
So, nande-deposit naman yung na-release na amount or the stable isotopes as the daughter material. So, that is how we illustrate half-life. So I mentioned a while ago how scientists do this measurement of half-life, of radioactive decay. So in a rock sample, they try to measure the presence of these radioactive particles. So definitely in that specific rock, there must be...
A parent material and a daughter material. So they compare the amount of the parent material and the daughter material with the half-life of the parent material. So once they are... able to determine the amount of daughter material, they will try to compute back in time na kailang half-life kaya ito.
So, they will add up that and they will be able to determine the absolute age of that particular rock. So, absolute dating or radiometric dating. This knowledge that scientists and geologists do are so helpful for us to understand the history of our planet.
Ngunit napakadami pa natin hindi alam sa ating planeta. But we are trying to know the history because if we know our past, it can be our guide for our future. Maraming salamat sa inyong lahat at magandang araw.