Lecture 3: Origin and Early Evolution of Life Flashcards
Earth 4,600 Ma
Earth formed by the gravitational accumulation of dust and larger objects. The mass melts and begins to differentiate into the core, mantle and crust. Water vapour and various gasses are outgassed but do not accumulate due to the great heat and continual bombardment as new material is accumulated. The Moon forms during a major collision.
Ma =
million years ago
Earth 3,750 Ma
Age of the oldest rocks on Earth (Isua Supercrustal Group form Greenland). Earth has cooled to the extent that a crust begins to solidify. As temperatures continue to fall the oceans and atmosphere can potentially begin to condense out.
Earth > 3,800 Ma
Progress retarded by continued bombardment of large objects. Released energy is sufficient to boil off the oceans and atmosphere (along with any prebiotic organic compounds)
Earth < 3,800 Ma
Meteorite bombardment decreased in intensity and the plant cool below a threshold that allows oceans and atmosphere to condense out. Organic compounds begin to be synthesised and accumulate.
By 3,800 Ma we have..
conditions on planet earth we believe suitable for life to have originated (?RNA world?)
Earth 3,500 Ma
The earliest fossil evidence for life on Earth
Approaches to solving the origin of life:
1) Analyse living prokaryotes&attempt to reconstruct their common ancestor (essentially the simple conceivable prokaryote)
2) Compare duplicated genes potentially enabling us to reach back beyond that ancestor & estimate some of the earliest components of genetic machinery
3) Reconstruct conditions that existed on Earth in these remote times & simulate these experimentally & see what is produced
Prokaryotes are believed to have originated before eukartoyes because:
1) they appear earlier in the fossil record
2) They are simpler in virtually every aspect
3) There is evidence that eukaryotes evolve form prokaryotes
Fundamental similarities between prokaryotes and eukaryotes include:
1) the method of transmitting information in triplet code in DNA and translating it into proteins through RNA
2) In living organisms all a.a are laevo-rotatory and in nucleic acids all the sugars are dextro-rotatory
Chemicals produced by simulating conditions on the primitive Earth:
- Amino acids (including all of the biologically important ones)
- Purines/Pyrimidines (inc. 4 bases of RNA [A,C,G&U] but not thymine which replaces uracil in DNA)
- Sugars
- Porphyrins (molecules which are the forerunners of important biological compounds like vitamin B12, chlorophylls etc)
- Coplex tar-like substances which defy analysis
Life most likely evolved through ________. There are a variety of possible environments in which life could have formed & a number of possible energy sources:
basic chemistry Necessary materials were available. -sun -radioactivity -electric discharges (e.g. lightening) -Volcanic (hot springs etc)
All living organisms use the same basic machinery:
information is stored in DNA & transcribed & translated into protein using RNA
What came first DNA or proteins?
given that proteins are the end product but are essential as enzymes in translating and copying the information in DNA.
- A dramatic breakthrough occurred in the 1980s when when self splicing RNA was discovered.
- Speculation on the origin of life began to centre on a “RNA world”.
self splicing:
Term describing an intron able to excise itself precisely from the RNA precursor without the involvement of any proteins. The capacity to carry out this reaction is thus specified by the intron RNA itself.
