Ozone layer and eukaryotes show up in the Proterozoic eon Ozone Layer and Eukaryotes Show Up in the Proterozoic Eon. Great Oxygenation Event (Oxygen Catastrophe)
Ozone layer and eukaryotes show up in the Proterozoic eon
- We left off in the last video in the Archean eon,
- where Arche comes from ancient Greek, meaning beginning or origin,
- and it's the eon in which either life first starts to exist,
- or at least it's first starts to somewhat flourish,
- it's possible that maybe life starts to exist
- at the end of the Hadean eon
- and of course, this boundary is big.
- The Archeon is also the first eon
- where we still have rocks from that time.
- So we are able to find rocks that we can date to be roughly
- 3,8 biliion years. The other really interesting thing
- that happened in the Archeon eon that really has a profound
- effects once we get to the Proteozoic eon
- is that you start to have cyanobacteria
- to produce oxygen. We've seen in the last video
- that they were producing oxygen but most of that oxygen
- was being absorbed by iron in the oceans.
- But what happens as we enter into the Proteozoic eon,
- Proteozoic eon, it's right over here as you can see
- we write it Pro-teo-zoic,
- we are now in the Proteozoic eon.
- That starts up about 2,5 billion years ago
- and Proteotoic comes from the Greek
- for earlier life.
- I'm not a Greek scholar, so you know,
- forgive me if I'm not getting the translation exactly right.
- But what's really interesting about the Proteozoic eon
- is that that oxygen that was being produced by that cyanobacteria
- at some point begins to saturate the iron
- and any other molecule that could have absorbed before.
- And once it is saturated, it starts to get released into the atmosphere.
- So the oxygen starts to get released
- and accumulated in the atmosphere. We think this happened
- to start to happend about 2,4 biliion years ago.
- So 2,4 biliion years ago
- oxygen begins to accumulate in the atmosphere. And of course, you know
- these days they may have been moved around a few hundred milion years
- as it gets more and more detailed. But this is the current understanding
- of when things happened. Maybe we will look at the geological records
- and fossil records that will move things around in the future.
- I can only imagine that 50 years from now or 100 years from now
- somenes still watching this video and lot of these might say
- hey, now we have found later that oxygen started to accumulate in the atmosphere
- earlier or later or that Eucaryotes occured earlier or later,
- but this, as far as I can tell, is our best current understanding.
- 2,4 biliion years ago oxygen begins to accumulate
- in the atmosphere. And what is interesting
- about this is once it accumulates, once it has come
- critical amount of oxygen in the atmosphere,
- and I touched on this in the last video, about 2,3 biliion years ago
- we have something called the great oxygenation event.
- Sometimens called the oxygen catastrophy. And this is right here,
- 2,3 billion years ago or 23 hundred milion years ago
- the atmosphere becomes oxygen-rich.
- Not as rich as our current atmosphere,
- But it becomes oxygen-rich enough that at least the environment
- becomes suitable for eucaryotic organisms
- or eucaryotic cell. Now, the other interesting thing that we might not care
- so much about it because we needed the oxygen, is that we think that
- this was actually the greatest extinction event in the history of Earth.
- That's what is called the oxygen catastrophy.
- So right over here, 2,3 billion years ago, a shouldn't giggle about this,
- this is a serious matter, this it the greatest,
- the greatest extinction event
- in Earth's history!
- In History. And I'll do history with capital H.
- In the history of the Earth. And that's because of
- the cyanobacteria producing lots of oxygen, eventually saturates the iron
- it accumulates in the air, once it gets to enough concentration
- it begins to actually suffocate. It's poisonous
- to most of the other organisms on the planet
- that were anaerobic, that they did not need oxygen,
- they actually found oxygen poisonous.
- Now, but since we have oxygen there's two interesting things that happened
- once that oxygen accumulated did other than causing this
- that mass extinction. There are actually three interesting things. Two of them
- are essentially crucial to us eventually showing up
- on this planet. The first is that it becames
- suitable now for Eucaryotes to exists.
- Eucaryotic organisms. Remember, these are organisms that have
- the nuclear membranes around their DNA, most Eucaryotes have other
- organelles like mitochontria. They need oxygen.
- They need oxygen.
- You can go to the biology play there we actually talk about respiration
- that occures in the mitochondria and that is obviously
- a process that needs oxygen. So when we have
- oxygen in the atmosphere we're starting to have
- an environment where Eucaryotes could at least exist
- and based on the fossil records on what we looked the DNA has changed
- over time, I'll do more videos on that, we think that
- the first Eucaryotes showed up about
- 2,2 billion years ago, althought there is some debate here,
- there is some evidence that it might have been a little earlier, a little later,
- I'm sure that number will be refind. But, you know,
- give a take of few hundred million of years,
- one procaryot got engulfed by another procaryot
- and say 'hey, we do pretty well living together'
- lot of the current theories that mitochondria has actually descended
- the current theory is that mitochondria actually descended from
- kind of an ancient procaryotic cell, an ancient bactery actually has
- its own DNA. Actually your mitochondrial DNA
- is passed down from your mother and your mother's mother
- and your grandmother's mother and so on. It's kind of another
- little animal living inside of a larger cell.
- And we are Eucaryotes. We needed this to happen.
- The human body is not one eucaryotic cell. We're made up of trillions.
- It is estimated to 50 to 100 trillion eucaryotic cells.
- So these are our ancestors that had to
- come into being at that time. Once again, all of this
- is happening inside of the oceans.
- The other interesting thing that happened. Remember, we were being bombarded
- with UV radiation from the sun. So if you are on the land,
- let me draw the land and the ocean.
- So here is the ocean and here is the land.
- Here is the land righ over there in yellow.
- Constantly being bombarded with UV radiation.
- UV stand for ultraviolet. It is even more violet than purple.
- So it is constantly being bombarded with ultraviolet radiation
- from the sun which is very inhospitable to DNA
- and to life. So the only life at this point could occure
- in the ocean where was protected to some degree from the UV,
- the land was just open to it.
- Anything on the land was just irradiated.
- The DNA would get mutated, just would not be able to live.
- So what I guess had to happen, and the reason why
- are we are able to live on the land, is that we have an ozone layer.
- We have an ozone layer up in the upper atmosphere
- that helps absorb, that blocks
- most of the UV radiation from the sun.
- And now the oxygen began to accumulate. We had the oxygen catastrophy,
- oxygen accumulates in the atmosphere, some of that oxygen
- goes into the the upper atmosphere. So we are now in this time period.
- It goes into the upper atmosphere, it actually reacts with the UV light
- to turn into ozone which then can help
- actually block the UV ligt. I'll do another video
- on the ozone-oxygen cycle. So this oxygen production
- is crucial one to have an ozone layer,
- so that eventually life can exist on the land,
- it is also crucial because eucaryotic organisms need that oxygen.
- Now the third thing that happened and also being a significant event,
- we believe that that oxygen that started to accumulate in the atmosphere
- reacted with methane in the atmosphere,
- and methane is a greenhouse gas. It helps retain heat
- in the atmosphere. And once it reacts with the oxygen
- and starts dropping out of the atmosphere as methane, we believe
- the Earth cooled down and it entered its first
- and some people believe its longest snowball period.
- So that's what they talk about here in this diagram.
- The first snowball Earth. It's sometimes called the Huronic glaciation.
- That happened because we were unable to retain the heat
- if that theory is correct. So as the theory goes,
- the whole Earth essentially just iced over.
- So as we go through the Proteozoic eon,
- I guess the big markers of that, this is the first time
- that we have an oxygen-rich atmosphere.
- The first time that Eucaryotes can come to existence
- because now they have oxygen, I guess we can say, to breath.
- The other big thing is that this is where the ozone forms.
- It kind of sets the stage for the next eon.
- For animals or for living things to eventually
- get on to the land. I will talk about that in the next video.
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At 5:31, how is the moon large enough to block the sun? Isn't the sun way larger?
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