5 - 1 Geo Time Scale

Alright, this lecture is going to be looking at dating of rocks and understanding geologic time. So after you completed this in your binder, you should be able to understand and be able to use the laws and principles to determine relative ages and sequences of geologic events, be able to apply the techniques of radiometric dating to determining the numerical age of a rocker mineral and describe the geological timescale and list. The proper sequence of the major events that have taken place since. Earth formation and then recognize that Earth's history is detailed by the rocks, the fossils and the structures that we see in the Earth's crust today by being able to understand the structures we can precisely, or we can understand precisely what happened. And when it happened in the past so here's, our geologic piece that the earth can change in the blink of an eye.

When we look at natural hazards that it's important understanding energy in the event in the duration of time that time and energy. Help describe what took place, but you know whether whether we define it as an event, which is a large amount of energy in a short amount of time or an episode a low amount of energy in a long duration of time. At the end of the day, whether it's an event or episode the end result changes the Earth's surface in some way. And many of these are contained in Earth's rocks. So we use the rocks to determine what was taking place in asteroid impact. The very high-energy event, short amount of time a volcano. Can be moderate to high energy, but a very short amount of time, a mega flood once again, another high energy, but a short amount of time we can talk about ice ages, ice ages are low energy, a very large amount of time.

And one could even say that a transgression regression of sea level change would be very low energy, a very large amount of time. So we're looking at it in terms of time. And then here are the principles we are going to be applying here.

I want to make sure that we see that we can apply all. Of these that are at our next couple slides here that unconformities also are features that tell us that well something was happening here that rock was not being deposited. It was an erosional environment. And this here happens being angular unconformity. Whereas this happens to be a disc conformity disc informing member, sedimentary rocks, horizontal over some erosive boundary over horizontally Lane, sedimentary, rocks and non-conformities.

Here we have horizontal sedimentary rocks in this picture. Right here this non can pharma t, this is remembered. These are all three are examples of unconformities, but non tells me that sedimentary rocks lay down within or over igneous and or metamorphic and that's. The key those are the differentiators I want you to notice that even in this picture right here in the sedimentary rock above the igneous metamorphic, you have inclusions, you have pieces of those rocks inside here. So moving on when I start putting all of these features together, I get these rock. Strata sequences here I have a timeline here, and you can just follow with me. A is the elder than B then d than e. It then gets cross-cut by a dingus intrusion.

Letter. C h is a fault that that disrupts able and see in here. The Cygnus intrusion here was caught. This is a fault also a cross-cutting relationship.

And then I have this feature right here. This is an unconformity. And if I go back to it, let's, see, I, horizontal, sediment over horizontal sediment that implies that I'm looking at a disc. Conformity so we're, really putting it all together. And then the youngest layers are F and G, so we're starting to put them all together. And so now we're going to start adding the radiometric dating beats that if I start looking at my ratios, right? The ratio of parent to daughter, I can then couple that with understanding the timeline of the event that took place and I can put a very, very specific time to it.

Remember, the decaying radioactive parent is going to be decreasing while the stable daughter is. Going to be increased. And so over time I get these ratios simply by interpreting this graph. And so I put a timeline to it so here's where I can put it all together. When I look at the geologic timescale, I can go and look at okay. Precambrian is roughly eighty-eight percent of all of Earth's history that the Phanerozoic eon right, we're talking eons here, the eons are your large groupings that we're currently in the Phanerozoic eon that the Precambrian is so vast it subdivided into the.

Hadean the Aryan and the Proterozoic just based on what was taking place in geologic time. So the Phanerozoic is what gets the most kind of it's got the most famous is where we are. Now, this is where light we get multicellular organisms that that kind of separate the timeline of the Precambrian to the Cambrian. And so we get multicellular material right fossils. And it took several billion years to get here. Some of the earliest fossils are found between you know, 3.8 and 3.4 billion years ago, we're. Way back here in the Precambrian, and it took us a few billion years for the single-celled organism to kind of master cellular processes.

So we go from single-celled organisms that were primarily photosynthetic to now aside interpreting Break into the Phanerozoic eon, right? As we start moving into the Cambrian. We start seeing organisms with shells. We start getting more complex life and that's.

The timeline that's, the window that's, the age of invertebrates here. And then as time continues. Go on I've got the Cambrian Ordovician, slurry and Devonian, Mississippi and Pennsylvania and Permian. These are all apart here of what I call the Paleozoic era.

Right? This is an era. So we have eons, and we have errors or subdivisions and I can even subdivide those into the period. So we looked within the Paleozoic or have the Cambrian Ordovician. This sequence here.

These are the periods. These are subdivisions, so I have the age of invertebrates I've trilobite that lived here. I have some. First fishes here, I start getting some of the first land plants, notice that that marks the difference between Ordovician Silurian, and the plants would have looked nothing like we think up today. We have fish that dominate their glitters they're all they're all over. They're starting to get more complex.

Then we find our first insect fossils. We start. We start.

Furthermore, we start getting just an evolutionary sequence, and we know this because we find the faces we can study what's going on here. Furthermore, we have our. Age of amphibians at the extent at the end here with no more trilobite Tsar found so that's, why trilobite so very nice index fossils, because it tells us a lady lived within this.

This like 160 million year window, maybe it's closer to 200, but trilobite only lived in this timeframe. And then we start having dinosaurs. So this is where we start think of Allah, Wow dinosaurs, right, Jurassic Park. So we have the Triassic Jurassic Cretaceous. Those are the periods within the Mesozoic era. And this is.

The age of reptiles, and then we have this event that takes place picks t5 million years ago. And it says asked asteroid that hit the Yucatn Peninsula. And after this point, we start labeling epics. We have these. We have information that we have.

Well, let's just say we have a lot of kinds of our mammalian history taking place in our more recent time. So within the past 65 million years there's, even a new division, a new division of an epic right periods are subdivided even further. And then we eventually.

We are up here at this line right here we are currently in the Phanerozoic eon, the quaternary period, the Holocene epoch, oh I, skipped, the Cenozoic era, sorry. So Phanerozoic, eon, Cenozoic era, the quaternary period in the Holocene epoch like that's, our current time frame. So if I break down the geologic time again, so I'm looking at IAN's eras periods and epochs the eons there have been two eons through geologic time, the Precambrian in the Phanerozoic.

So, but the Precambrian is so vast it's been divided. In the Haiti that was literally the bombardment phase of the earth when it was organizing due to gravity that is literally being blasted by asteroids. Comets me just anything that large bodies that were gravitationally bound to the earth began to collide with it.

And that was really the building of Earth are can we have the earliest life-forms? We find that we don't know exactly what this primordial soup it's kind of a theory. But we do start finding fossils from the oldest. Fossils, roughly 3.8 billion years ago. Now we have the Proterozoic that's where our atmosphere begins changing changing changing due to photosynthetic organisms. That are just beginning to photosynthesize take sunlight.

And you know, photosynthesis was taking place here and oxygen is a byproduct, and it began to build up. And this took a long time. It took a couple billion years to get our atmosphere, sustained a stable enough to be able to sustain complex multicellular life. Here I have Eris. The.

Phanerozoic era is divided into Paleozoic that's. The ancient light, we have Mesozoic. This is consistent with your kind of dinosaur world. And then we have sent avoid that's the more modern world. Ok, here goes Paleozoic, ancient time, Paleozoic era. Here we have observed how life-forms were evolving and changing.

And this is evidence from studying from and radiometric dating the age of rock. So we have this kind of history here of the Paleozoic ancient life, well, they're, very, very significant. Because this is where we get our fossil fuel region in the carboniferous period during the Mississippi and in Pennsylvania. And this is just the time when where plants were let's just say they were these warm swamps.

The shallow swamps were just photosynthesis was cranking out these plants, and they were just being buried, and they were contained, and they eventually evolved from your new your process of cola fiction as you go from plants into your feet into lignite into the two meanest and. Then over time, anthracite coal that this was all taking place a lot of our most of our fossil fuels. We get on earth or from these this age of rocks, you find this age of rocks, you have the chance of having these fossil fuels. And lastly, Mesozoic ox is not a slit. Lastly, but dinosaurs rule.

They for about 185 180, 200 million years. And what we have here is the Triassic Jurassic Cretaceous. And this is in the age of reptiles that the age of dinosaurs ended about 65 million years ago. We have evidence of.

This from this impact of the Yucatn Peninsula, and we have shocked quartz as an indicator. It tells us that something big happened. There's also layer of iridium that is consistent with cosmic debris. And yet it's uncommon in the Earth's crust. So when you find it in one specific layer consistent across the earth, you know that something took place, but at the same time, there were flowering plants that were taking off right? We have some of these flowering plants.

And there were basalt flows. That were changing the atmosphere right? We have val ken isn't taking place.

So maybe could all three of these features all had something to do at the end of the dinosaurs, I, don't know, I wasn't around to see it. So, but that's kind of right here, I think, there's more than one just that it might not have just been one event. Now that would have been a awful event. Right? One bad day on earth, but asteroids and comets in these craters they're, not uncommon on earth. You know, think of this all of these. Dots you see here, these are existing craters that we see today from impacts craters.

Remember, the earth is only covered by thirty percent land. So that means we're looking at only thirty percent of all the cratering from impact craters that in theory, they hit the earth they're going to be randomly distributed. That means our oceans have taken a lot of bombardment too. So if we talk about this one right here, this is a new Yucatn Peninsula in Mexico. This is what it looks like.

This is a topographic map that this is the northern peninsula here. And this is what it currently looks like here today. And these are maps of what it looks like underwater. And we have this nice iridium layer that is uncommon in the Earth's crust. That is very reflective of the composition of the asteroid itself.

That's, a wonder where we find this iridium. We can say, yeah, something major happened, and it's consistent because it blanketed the entire Earth and last, but not least now we look at the. Cenozoic, and this is working winds evolved within the age of mammals. And you know, when I look at the Cenozoic, we've got kind of tertiary and quaternary. These are the periods that we're looking at, but it's been subdivided. We have a lot more history recently, it hasn't had time for to be broken down and eroded.

So our just like our memories when we create our own timelines, we know it. We remember a lot more took place today and yesterday in the day before than we did. Then we do three years ago, 10.

Years ago and 15 years ago. So you know, we've got more memory here, so it's kind of consistent with our own personal timelines. So I want you to consider a concept that when we look at dinosaurs live for a rule for 180 million years ago, and I would say, well, does that make them successful right? They're extinct now, or they've kind of evolved into what we see is birds today? But our humans are we and our intelligence are these determining factors for success civilization.

And humanity is about.10,000 years old. So we have the tools though today to destroy human life in many ways are we successful is the current modern-day of where we are in terms of intellect, and in with our brain capacities and being able to explore the earth. And our cosmos does that make us successful. You know, does do 1.8 million years of kind of hominid ancestry or evolution does that make us successful?

No maybe you'll have the answer.