Origin of cells

the pre-biotic atmosphere

no life, only traces of oxygen, high methane and carbon concentrations

high methane concentrations due to…

intense volcanic activity and meteorite bombardment

high carbon concentrations due to…

emissions from volcanos

higher temperature and light penetration

carbon dioxide and methane are heat-traping greenhouse gasses ex. hot springs and hypothermal vents in oceans

the stratospheric ozone layer

currently protects us by absorbing uv would not have existed because of the lack of oxygen

vents

are commonly found near in volcanically active areas. ALong with heat energy the vents secrete a ready support of reduced inorganic.

difference between living and non-living

living things use energy to keep themselves in a highly ordered state, are self-sustaining, passing the ability to maintain a highly ordered state to offspring, can divide to produce more cells,

spontaneous generation of life 

the first cells must have arisen from non-lilving material or life was transported here from elsewhere in the universe 

reducing atmosphere

low oxygen, only methane, ammonia, water vapor, carbon dioxide, it favored chemical reactions that add electrons to molecules

primary energy sources on early earth that facilitated chemical reactions 

1. solar radiation

2. geothermal heat from volcanic activity 

3. electrical energy from lightning. 

water

acted as a solvent for chemical, reactions, provided a medium for molecules to move and collide, helped stabilize formed compounds

simple organic molecules that could form under pre-biotic conditions

1. amino acids

2. nucleotides

3. simple sugars

early earths environments that facilitated chemical reactions 

1. hydrothermal vents

2. tidal pools 

3. volcanic hot springs 

why spontaneus formation of organic molecules is unlikely on modern earth?

1. presence of oxygen, which breaks down organic molecules

2. ozone layer blocking uv radiation

3. stabilized environmental conditions

J.B.S Haldane hypothesis

variety of organic molecules are made when ultraviolet light acts on a mixture of water→ based on the assumption that the atmosphere contained water vapour, carbon dioxide and ammonia

Stanley Miller and Harold Urey experiment

they mixed methane, hydrogen and ammonia and added water vapour.Then used electrical discharges to stimulate lightning. Mixture was allowed to cool and after one week simple amino acids and complex oily hydrocarbons formed. 

Vesicles 

small droplets of fluid enclosed in a membrane mainly composed of phospholipids

exosomes 

extracellular vesicles 

phospholipid molecule

hydrophilic head- attracted to water because its polar

hydrophobic tails- attracted to non-polar substances

when they are mixed with water phospholipids naturally form spherical bilayers

amphipathic molecule

molecule with both hydrophilic and hydrophobic parts

RNA 

can store information in the same way as DNA but it is self-replacing and it can act as catalyst because it can form complex three-dimensional structures that can undergo precise interactions with other molecules

ribozymes

ribonucleic acid enzymes, they have the ability to catalyze specific biochemical reactions, including RNA splicing in gene expression.

The RNA world hypothesis

suggests that RNA may have been important in the evolution of pre-biotic self replicating systems

Species using the same code

they inherited it from a common ancestor

convergent evolution 

evolution of strikingly similar structures in organisms that do not have a recent common ancestor 

LUCA

the last universal common ancestor

natural selection

extinction of other forms of life due to competition from LUCA or species that evolved from LUCA

Palaeontology

the scientific study of ancient life through fossils like rocks, it has provided the priceless evidence about the pathways of evolution, so it is an obvious approach for dating the first living cells and the last common universal ancestor

The Strelley Pool Formation

3.5 to 3.0 billion-year-old rock layer in Western Australia, large structures that resemble fossilized stromatolites have been discovered in these rocks

stromatolite

It forms when clusters of cyanobacteria in shallow seawater trap sediment and secrete calcium carbonate, slowly building rocky mounds over thousands of years. However, simpler life forms exist than the bacteria that form stromatolites, so we can deduce that earlier cells must have existed before 3.42 billion years ago.

why there are no rocks older than 4gya?

because tectonic processes continuously destroy them by subduction and create new rock from magma.

sedimentary rocks 

when rock is ground down by erosion the hardest fragments can persist and become part of new sedimentary rocks 

planet theia

first living cells existed soon after the earth is thought to have been impacted by the planet Theia. This impact would have sterilized the earth and led to formation of the moon.

bacteria and archea

groups of organisms that originated early in the history of life in which researchers have identified genes that occur widely

Luca had a gene 

if an evolutionary tree is constructed for a shared gene and it matches the accepted evolutionary tree for bacteria and archea deductive reasoning tells us that a gene has been inherited from a common ancestor of bacteria and archea. 

genes in LUCA

355 gene filaments needed for anaerobic metabolism and for fixing carbon dioxide and nitrogen, from this we can deduce that LUCA lived in an environment with high. concentrations of hydrogen, carbon dioxide and iron (found in hydrothermal vents)

hydrothermal vents

cracks in the earth’s surface,, characterized by gushing hot water carrying reduced inorganic chemicals such as iron sulfide.

the hydrothermal fluids

• emerge at 60 to 90 degrees

• contain high concentrations of hydrogen, methane, ammonia and sulfides → represent readily accessible supplies of energy which early cels would have needed to assemble carbon compounds into polymers