1. THE ORIGIN OF LIFE

2. 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

3. 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

4. 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

5. 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)

6. 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

7. 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

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

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

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

16. 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

17. 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

18. 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

19. 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 )

20. 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????

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

22. 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

23. 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

24. 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

28. 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

29. 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)

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