Beginnings of life Life and photosynthesis start to thrive in the Archean Eon
Beginnings of life
- We finished off the last video in the Hadean Eon.
- It was named for Hades or the ancient greek Underworld
- Hades is also the name of the guy who ran the ancient greek underworld
- Zeus's older brother and it was an appropriate name,
- although the idea, the ancient greek notion of the underworld
- isn't exactly the modern notion of hell, but it was a
- hellish environment, you had all this lava flowing around
- and things impacting the earth from space. As far as
- we can tell right now it was completely inhospitable
- to life. And to make matters worse, even though the
- earth started to cool down a little bit, maybe the crust
- became a little bit more solid, maybe the collisions
- started to happen less and less as we started to go
- a few hundred million years fast forward after
- Theia ran into the early earth and formed the moon
- There is something like the "Late heavy bombardment"
- and right now the consensus is that life - whatever we
- are descended from - would have had to come about after
- the late heavier bombardment, because this was a time when
- so many things from outer space were hitting earth,
- it was so violent, that it might have killed off any
- kind of primitive, self replicating organisms or molecules
- that might have existed before it. And I won't go into
- the physics of the late heavy bombardment.
- What we believe of what happened, because Uranus and
- Neptune, so this is the sun right here, That is the sun.
- This is the asteroid belt. That's outside the orbit of the
- inner rocky planets. But Urans and Neptune,
- their Orbits moved outward. What that caused is
- gravitationally it caused a lot of the asteroids of the
- asteroid belt to move inward and started impacting
- the inner planets, and earth was one the inner planets.
- And also impacted the moon. It also obvious on the moon
- The moon doesn't have an atmosphere to smooth over the
- impacts. The consensus is that only after the late heavy
- bombardment was Earth kindof ready for life.
- We believe that the first life formed 3.824 billion
- years ago. Remember, G for Giga, 4 billions years ago.
- When we're talking about life in this period, we're not
- talking about squirrels or panda bears. We're talking about
- extremely simple life forms. Prokaryotes.
- Let me give you a little primer on that.
- We're talking about Prokaryotes. I'll compare them
- to Eukaryotes.
- Prokaryotes are for the most part unicellular organisms
- that have no nuclei. They also don't have any membrane
- bound organelles, or what we would call parts of the cells
- that would perform specific functions, like Mitochondria
- So their DNA is just floating around.
- Let me draw this character's DNA.
- So it's just floating around ,just like that.
- Prokaryote literrally means : "Before kernel" or
- "Before Nucleus"
- Eukaryotes DO have a nucleus with all their DNA.
- So this is their nuclear membrane with the nuclear
- DNA floating inside it
- It also has other membrane bound organelles, Mitochondria
- is kindof the most famous of them
- Mitochondria, we think is basically one prokaryote
- crawling into the membrane of another and becoming stuck
- and they both becoming a symbiotic organism with each other
- So at this time we're still talking Prokaryotes at this stage.
- This shows our current understanding of where things
- branched off from, at this point of the tree
- is some common ancestor to prokaryotes and eukaryotes
- prokaryotes right over here
- the bacteria and archeae
- and here is the eucaryotes
- and this first living thing we think might have been
- some self replicating molecules, maybe a little bit more
- organized membrane, DNA and RNA became
- the method of passing information from one generation to the next
- It is still an open question what that first life is
- or how you even define that first life
- Based on the makeup of DNA molecules of the current
- organisms, this is how the think the tree of life came about
- We have one common ancestor, then the Archeae and Prokaryotes
- have a common Ancestor, it's different from the Bacteria
- this is an example of Bacteria, Ecoli
- We think that the earliest lifeforms we anaerobes
- these did not need oxygen and for the most part
- found oxygen poisonous and the earliest
- lifeforms probably also did not perform photosynthesis
- They might have gotten their energy from other sources
- Chemically probably in that extremely volatile
- environment that they were in
- Lets forward to a major event, these are big time scales
- we are talking about here
- This is a big timescale, we're talking about 800 million
- years, humans and chimpanzees have ony
- diverged 5 million years ago
- From ancient greece to now we're talking about only
- 2,500 years ! You multiply that by 1,000 you get
- 2,5 million years.
- And this is 800 million years !
- These are extremely huge periods of time.
- That's why we call them Eons.
- The dividing line between the Hadean Eon and the
- Archean Eon is a bit fuzzy.
- Most people place it at about 3.8 Billion years ago.
- It's about the earliest rocks we can observe.
- We have rocks from about that time.
- So there are 2 things, Rocks have survived and that is
- also when we think life has started. So now we are in the
- the Archean Eon.
- But there is still none to little oxygen in the Environment
- If you went to the earth at this time it would have looked
- something like this, a reddish sky. You would have had
- nitrogen and methane and carbondioxide in the atmosphere
- There would still have been a lot of volcanic activity
- This right here, these are pictures of stromatolites
- These are formed from Bacteria that are bringing in
- sediment particles, and over time these things get
- built up.
- The most important even in the Archean Eon in my opinion
- , we believe this happened about 3.5 billion years ago
- Prokaryotes, or especially bacteria evolving to use the
- energy from the sun
- To actually do photosynthesis
- The side effect from this was the production of oxygen
- And at first this oxygen didn't really accumulate in the atmosphere
- because there was a lot of dissolved iron in the oceans
- All of the life for the next billion years all occured
- in the oceans. There was no ozone layer.
- The land was being irradiated, a completely inhospitable
- environment for life.
- The first oxygen that got produced, instead of being
- released into the atmosphere instead bonded with the
- iron that was dissolved in the ocean
- Once a lot of that iron was oxidized later on and the
- oxygen did get released into the atmosphere it had
- a cataclysmic effect.
- Especially on the anaerobic life that existed until then.
- It was neccessary though for us to happen later on.
- Still a few billions years though before things start
- flopping around on the land. See you at 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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