A2.1: ORIGIN OF CELLS
4.5 billion years ago → force of gravity pulled rocks scattered around the Solar System into a
cohesive sphere = Earth
Earth cooled → water vapour in the atmosphere condensed → fell as rainfall to become oceans
Primordial soup → early oceans, rich in simple carbon-based compounds
↪ source of the first primitive life (approx 3.5 billion years ago)
→ primitive cell: lipid membrane and genetic material (RNA) that
can be passed onto offspring when it replicates
When life originated → the planet had a hostile environment:
● Asteroid impacts
● Widespread volcanic activity
● High temperatures
● No ozone layer
● Dusty atmosphere containing methane, ammonia, water vapour, a lot of CO2 and no oxygen
But what conditions were necessary to support the development of life on Earth from inorganic
molecules?
Conditions on early Earth
When life originated on Earth:
- Temperatures ranged from 75ºC – 95ºC
- There were no solid land masses, it was a single global ocean
- Comet and asteroid bombardment → brought water and other compounds to Earth
- Methane and ammonia were released in the collisions and the volcanic eruptions
- Atmosphere → mainly methane and ammonia + CO2 and H2O vapour
Lack of O in the atmosphere = no Ozone Layer
Inner Core of the Earth was liquid, ratchet than the actual solid one → increased motion = smaller
protective Magnetic Field → planet much more exposed to cosmic and solar radiation
Also, this lead to extreme meteorological events, mainly electrical storms
, Pre-biotic formation of carbon compounds
Necessary precursor to the origin of life → formation of simple carbon-based compounds
↪ precursor to more complex organic molecules that provide the
structural and functional components for cells to survive and replicate
Lack of O + presence of reducing gases = reducing atmosphere
↪ reducing gas: gases that donate e-, reducing that substance
⬇
enabled chemical reactions to take place
These reactions → formation of more complex carbon compounds:
● Simple amino acids
● Hydrocarbons
↪ joined to form building blocks of cells:
- Proteins
- Lipids
- Nucleic acids
Some of the more complex carbon compounds → developed ability to
self-replicate, and eventually became packaged into membranes
This allowed molecules to exist within different conditions to the
external environment = formation of cells
Early conditions on Earth are very different to those nowadays
Modern conditions on earth → DON’T allow spontaneous formation of biological molecules
4.5 billion years ago → force of gravity pulled rocks scattered around the Solar System into a
cohesive sphere = Earth
Earth cooled → water vapour in the atmosphere condensed → fell as rainfall to become oceans
Primordial soup → early oceans, rich in simple carbon-based compounds
↪ source of the first primitive life (approx 3.5 billion years ago)
→ primitive cell: lipid membrane and genetic material (RNA) that
can be passed onto offspring when it replicates
When life originated → the planet had a hostile environment:
● Asteroid impacts
● Widespread volcanic activity
● High temperatures
● No ozone layer
● Dusty atmosphere containing methane, ammonia, water vapour, a lot of CO2 and no oxygen
But what conditions were necessary to support the development of life on Earth from inorganic
molecules?
Conditions on early Earth
When life originated on Earth:
- Temperatures ranged from 75ºC – 95ºC
- There were no solid land masses, it was a single global ocean
- Comet and asteroid bombardment → brought water and other compounds to Earth
- Methane and ammonia were released in the collisions and the volcanic eruptions
- Atmosphere → mainly methane and ammonia + CO2 and H2O vapour
Lack of O in the atmosphere = no Ozone Layer
Inner Core of the Earth was liquid, ratchet than the actual solid one → increased motion = smaller
protective Magnetic Field → planet much more exposed to cosmic and solar radiation
Also, this lead to extreme meteorological events, mainly electrical storms
, Pre-biotic formation of carbon compounds
Necessary precursor to the origin of life → formation of simple carbon-based compounds
↪ precursor to more complex organic molecules that provide the
structural and functional components for cells to survive and replicate
Lack of O + presence of reducing gases = reducing atmosphere
↪ reducing gas: gases that donate e-, reducing that substance
⬇
enabled chemical reactions to take place
These reactions → formation of more complex carbon compounds:
● Simple amino acids
● Hydrocarbons
↪ joined to form building blocks of cells:
- Proteins
- Lipids
- Nucleic acids
Some of the more complex carbon compounds → developed ability to
self-replicate, and eventually became packaged into membranes
This allowed molecules to exist within different conditions to the
external environment = formation of cells
Early conditions on Earth are very different to those nowadays
Modern conditions on earth → DON’T allow spontaneous formation of biological molecules
