Lecture 3 - Early history of planet Earth Flashcards
What occurred 4,600 million years ago?
- gravitational accumulation of dust & larger objects causes the formation of Earth.
- the mass melts & begins to differentiate into core, mantle & crust.
- water vapour & various gases are out gassed but don’t accumulate, due to the great heat & continual bombardment as a new material is accumulated.
- the moon forms during a major collision.
What occurred 3,750 years ago?
- age of the oldest rocks on Earth (Isla Supercrustal Group from Greenland).
- Earth has cooled to the extent that a crust begins to solidify.
- As temperatures continue to fall the oceans & atmosphere can potentially begin to condense out
What occurred >3,800 years ago?
- progress retarded by continued bombardment of large objects.
- released energy is sufficient to boil off the oceans & atmosphere (along with any periodic organic compounds)
What occurred <3,800 years ago?
- meteorite bombardment decreases in intensity and the planet cools below a threshold that allows oceans & atmosphere to condense out
- organic compounds begin to be synthesised and accumulate
What occurred 3,500 years ago?
The earliest fossil evidence for life on Earth
How did the Early atmosphere form?
by volcanic outgassing of water vapour + N2 (+ its oxides). CO2, CH4, NH3, H2 & H2S.
- the water vapour gradually condenses to form the oceans and the H2 is lost into space.
What occurred after the early atmosphere formed?
eventually there was an Earth hospitable for life - atmosphere was not breathable at the start of the beginning of life
When did life begin?
between 3,800 & 3,500 million years ago
What is panspermia?
belief that life exists throughout the universe, distributed by space dust
What is the first approach to solving the origin of life?
Analyse living prokaryotes & attempt to reconstruct their common ancestor (essentially the simplest conceivable prokaryote)
Why is it thought that prokaryotes originated before eukaryotes?
- they appear earlier in the fossil evidence
- they are simpler in virtually every aspect
- there is evidence that eukaryotes evolved from prokaryotes
What are fundamental similarities between prokaryotes & eukaryotes?
- the method of transmitting information in triplet code in DNA & translating it into proteins through DNA
- in living organisms all amino acids are laevo-rotatory & in nucleic acids all sugar are dextro-rotatory
What is the significance of the fundamental similarities between prokaryotes and eukaryotes?
this means that it is very unlikely that live evolved twice - due to similarities between the two
What is the second approach to solving the origin of life?
compare duplicated genes (from before life evolved), potentially enabling us to reach back beyond that ancestor and estimate some of the earliest components of genetic machinery
What does LUCA stand for?
last universal common ancester
How would you compare duplicated genes?
look in archaea & bacteria for non-functional genes, and study them to find out how old genetic machinery worked
What is the 3rd approach to solving the origin of life?
Reconstruct conditions that existed on Earth on these remote times & simulate these experimentally & see what is produced
What are the chemicals produced by stimulating conditions on the primitive Earth?
- amino acids - including all of the biologically important ones
- purines/pyrimidines - all 4 bases of RNA formed - but not thymine
- sugars
- porphyrins - molecules which are the forerunners pf important biological compounds like Vitamin B12, chlorophyll
- complex tar-like substances which defy analysis
What does space contain that the atmosphere doesn’t?
laevo & dextro rotators forms. This can be seen in some meteorites
How is life likely to have evolved?
through basic chemistry on planet Earth
What are the variety of possible environments in which life could have formed a number of possible energy sources?
- sun (UV radiation)
- radioactivity
- electrical discharges (e.g. lightening)
- volcanic (hot springs, black smokers etc.)
What same basic machinery do all living organisms use to replicate?
information is stored in DNA and transcribed & translated into protein using DNA
How was the discovery of what came first - the protein or DNA - solved?
when self-splicing RNA was discovered
How did a concoction of chemicals end up in the ocean?
as RNA can self splice - all the organic compounds - e.g. uracil is being used by RNA
When are chemicals more abundant?
if they are not used by the replicators - this meant there was now competition for replicators to use other sources, which could’ve led to the development of life.
- there may have also been mutations in the RNA during replication
What led to the development of novel metabolic pathways?
when the ‘primordial soup’ ran out
What are chemoautotrophs?
energy from oxidising inorganic substance - e.g. H2S, NH3, Fe2+ etc. C source CO2
What are chemoheterotroghs?
energy & C source from consuming organic compounds
What are photoautotrophs?
energy from CO2
What are photoheterotrophs?
energy from light, C source from consuming organic material
What was required for the new metabolic pathways?
the synthesis of cytochromes (the basis or oxygen metabolism) & porphyrins & related compounds that are the forerunners of photosynthetic pigment (the chlorophylls)
What are Obligate anaerobes?
poisoned by O2, & live exclusively by fermentation or anaerobic respiration
What are aerotolerant organisms?
can’t use O2 for growth, but tolerate its presence * live by fermentation
What are facultative anaerobes?
use O2 if it’s present but can live by fermentation in an anaerobic environment
What are obligate aerobes?
use O2 for cellular respiration & cannot live without it
