THE ORIGIN OF LIFE

THE FORMATION OF LIFE This is highly theoretical but not a random guess – there has been lots of research We know more about the conditions of early Earth than about how specific organisms evolved

4.5-4.6 BILLION YEARS AGO- THE EARTH FORMS No oxygen! No oceans! No organic molecules No life! The Earth was extremely hot Lots of volcanoes Lots of comets/meteors

THE EARLY ATMOSPHERE Volcanoes spewed gases such as NH3, CH4, H2O (as a gas) and H2 into the air No oxygen About 4 billion years ago the Earth cooled enough for the gases to condense, forming the oceans

SIMPLE ORGANIC MOLECULES FORMED The energy from light, lightning and heat of the Earth’s core caused chemical reactions to occur Complex molecules like amino acids formed (the Oparin- Haldane theory)

THE MILLER-UREY EXPERIMENT Reproduced the conditions of early earth When they heated a flask containing the molecules of Early Earth organic molecules formed within a day Amino acids formed within a week

PREBIOTIC SOUP It it thought that organic materials collected in the oceans, forming the prebiotic (before life) soup Life is believed to have formed out of this ooze, though how this occurred is not understood

POLYMERS AND SELF-REPLICATING MOLECULES FORMED (RNA WORLD) It is currently thought that RNA molecules were able to form in the “pre-biotic soup” These RNA molecules might have been able to self-replicate, Very speculative

THE APPEARANCE OF PROTOBIONTS Non-living pre-cells Essentially organic molecules wrapped in a simple membrane They cannot reproduce and are not a form of life Thought to be an important step in the evolution of life

3.5-3.9 BILLION YEARS AGO – LIFE! Heterotrophic prokaryotes Did not use oxygen and built up CO2 in the atmosphere LOTS of competition so these prokaryotes evolved quickly

Autotrophic prokaryotes evolved 3.3 BILLION YEARS AGO Autotrophic prokaryotes evolved Bacteria that could photosynthesize Huge survival advantage Produced oxygen which dramatically changed the Earth’s atmosphere

THE OZONE LAYER FORMED O2 from photosynthesis interacts with UV light to form the ozone layer This prevented UV light from damaging living organisms Can also be used for aerobic respiration

AEROBIC RESPIRATION EVOLVED Mitochondria-like bacteria evolved Use O2 in the atmosphere to more efficiently break down molecules This allowed them to get more energy from food – another huge advantage in survival

ABOUT 1.5-2.1 BILLION YEARS AGO The first eukaryotes formed (single celled) Plants, animals, fungi etc. Organisms with organelles Endosymbiosis occurred

ENDOSYMBIOSIS Some organelles (nucleus, mitochondria, chloroplast) were originally free living cells They were engulfed by another cell, becoming organelles

ABOUT 1 BILLION YEARS AGO The first multi- cellular eukaryotes appear Probably after the evolution of sexual reproduction Thought to have possibly evolved from colonies of single celled organisms

A NOTE ABOUT MULTICELLULARITY It has evolved several (around 13) times in the eukaryotic lineage Plants and animals have different single- celled common ancestors Aerobic respiration seems to be a requirement for this to happen

ABOUT 600 MILLION YEARS AGO The first simple animals evolved in water Animals technically evolved before plants because plants are by definition terrestrial But photosynthetic organisms evolved long before animals

ABOUT 475 MILLION YEARS AGO Plants colonized land This paved the way for animals to come ashore It only took insects about 75 million years to do it And vertebrates about 115 million years (So don’t complain about a 40 minute lecture )

ABOUT 200 MILLION YEARS AGO Mammals evolved Came about 160 million years after amphibians and about 100 million years after reptiles But mammals evolved about 50 million years before birds (and 70 million years before flowers) Hadrocodium – the first mammal????

ABOUT 55 MILLION YEARS AGO The first primates evolved They were small, about the size of a squirrel

ABOUT 2.5 MILLION YEARS AGO The first members of the homo genus appeared Thought to be Homo Habilis but there is still a lot of debate about human evolution

ABOUT 200,000 YEARS AGO The first Homo sapiens sapiens (humans) are thought to have evolved Humans have existed for about 0.004% of Earth’s existence And about 0.005% of the time life has existed And 0.03% of the time animals have existed

The Earth’s early atmosphere forms (gases) The gases cool and the oceans form Simple Organic molecules form Polymers and Self-replicating molecules form Protobionts (pre-cells) form Heterotrophic prokaryotes evolve Autotrophic prokaryotes evolve Oxygen becomes common Eukaryotes evolve

WE BELIEVE ALL LIFE IS RELATED 1 tree of life Based on: A common genetic code Same basic molecules in all living things (amino acids, proteins etc.) Similar metabolic pathways

WE BELIEVE ALL EUKARYOTES ARE RELATED Based on: Similar membrane-bound organelles A cytoskeleton organizing the cell Linear chromosomes (compared to circular chromosomes of bacteria)

They show relationships by common ancestry A NOTE ABOUT TREES They show relationships by common ancestry Shape doesn’t really matter