THE HISTORY OF LIFE ON EARTH PART 1 UNIVERSE TO EUKARYOTES

EVOLUTION OF THE UNIVERSE  Origin is believed to be a dense tiny mass of energy and matter that was very unstable  BIG BANG  15 billions years ago an eruption of the mass causing local accumulations of matter due to gravity, some large enough to sustain thermonuclear reactions

 5 billion years ago, our solar system started as a cloud of matter that condensed  Center collapsed = sun  Further out aggregations = planets  1 st 2 = very hot  4 th very cold  3 rd warm = EARTH – enabled life to evolve

ORIGIN OF LIFE  SPONTANEOUS GENERATION = new life appears from non-living matter, was accepted into 1800’s but then gradually disproved  1688 Redi disproved a maggots-from-meat, 1860’s disproved broth-to-microbes  ’s Poarin & Haldane proposed PREBIOTIC EVOLUTION = life arose from non-living matter through ordinary chemical reactions

PREBIOTIC EVOLUTION  Hot earth cooled and compounds formed = carbon dioxide, water, methane, ammonia, hydrogen, nitrogen etc.  no free oxygen gas which breaks down organic molecules easily  Lots of water accumulated  Lightning, volcanic heat & UV from sun = energy into waters

 1953 Stanley Miller simulated mix from previous slide  simple organic molecules formed  No oxygen results in accumulation of organic molecules in seas  “nutrient soup”  Evaporating pools became concentrated  molecules for first living cells and food for them

RNA – FIRST SELF-REPLICATING MOLECULE ?  There are RNA molecules that act as enzymes and cut apart RNA and make more RNA = RIBOZYMES  Probably arose by chance and made errors (mutations) when coping themselves  protein enzymes by mutation or DNA by mutation to safeguard against attack by other RIBOZYMES  RNA  PROTEINS  DNA

 Organic molecules are synthesized abiotically  Small RNA chains form and some can catalyze ther own replication using free ribonucleoids  Mutations allow ribozymes to catalyze protein synthesis from free amino acids  more efficient enzymes  Mutations allow Ribosomes to copy themselves into more stable DNA which becomes permanent storage of genetic info, RNA becomes intermediate between DNA and proteins Ribonucleoids, amino acids, lipids, sugars Self-replicating RNA “ribozymes” RNA ribozymes  protein enzymes DNA  RNA  proteins

FIRST LIVING CELLS  When proteins and lipids are agitated in water  hollow MICROSPHERES form that resemble cells because:  Well-defined boundary  Form a membrane  Absorb materials from solutions (feed)  Grow  Divide by splitting

DID ALL THIS ACTUALLY HAPPEN  There was enough time  Most biologists conclude that the origin of life is an inevitable consequence of working with natural laws  However, none of this has been proved and probably never will

THE AGE OF MICROBES 3.5 BILLION YEARS AGO  500 MILLION YEARS AGO

PROKARYOTES  Arose 3.5 BYA  Nutrients & energy from abs. Primordial soup  No free oxygen = anaerobic metabolism = anaerobic bacteria  Used up energy mol. In “soup” leaving carbon dioxide and water (low nrg)  Photosynthesis evolved  Oxygen began accumulating in atmosphere reaching high levels 2 BYA  Aerobic metabolism evolved with advantage over anaerobic cells because more energy released

Anaerobic bacteria Anaerobic bacteria (no oxygen, lots nutrient soup) Use up energy molecules in soup Photosynthetic bacteria = cyanobacteria (make energy & oxygen) Change atmosphere to oxygen Aerobic bacteria (lots oxygen, make more energy)

EUKARYOTES  Primitive predatory bacteria appeared next that could not photosynthesize or undergo aerobic metabolism  engulfed bacteria and digested them  1.4 BYA a predatory bacteria gave rise to first Eukaryotic cell. HOW? Read on !

ENDOSYMBIOTIC HYPOTHESIS  Certain types of bacteria evolved into chloroplasts and mitochondria after they were engulfed by predatory bacteria  Nucleus is more obscure, but perhaps originated by in folding of cell membrane to protect the genetic material