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 condensedCenter collapsed = sunFurther out aggregations = planets

1st 2 = very hot4th very cold3rd 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 disproved1688 Redi disproved a maggots-from-meat, 1860’s

disproved broth-to-microbes1920-1930’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 boundaryForm a membrane

Absorb materials from solutions (feed)GrowDivide 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 bacteriaAnaerobic 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