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THE ORIGINS AND VARIETIES OF LIFE ON EARTH. How was life first created?. HST101: Lecture 7 Craig Benjamin. What were the first living organisms like?. Where and when were the first organisms created?. But first … where are you now professor??. Vancouver Island, British Columbia, Canada.
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THE ORIGINS AND VARIETIES OF LIFE ON EARTH How was life first created? HST101: Lecture 7 Craig Benjamin What were the first living organisms like? Where and when were the first organisms created?
But first … where are you now professor?? Vancouver Island, British Columbia, Canada
Vancouver Island is covered by a great diversity of complex life forms. Where did they all come from? Go surf it for yourselves!
Particularly the very strange life form of homo sapiens?? Where did they come from??
The Origins of Life Some traditional answers: • Gods created living things, one by one • Fermentation, spontaneous generation • Dreams www.angelfire.com/trek/ archaeology uwacadweb.uwyo.edu www.pcworld.com
Pt. 1: Early scientific explanations of the Origins of LifeA) Spontaneous Generation • Aristotle: • Life was generated spontaneously from ‘non-life’? • How to make life: • Take a sweaty shirt (or some rotten meat) • Leave it in the sun for a day or two • Voila! Maggots!
Food insulated from the air A Puffball mushroom releases spores Testing the Idea of ‘Spontaneous Generation’ • 17th century scientists tested the idea by • Boiling foods (to kill existing germs) • Insulating them (to avoid infection) • To see if life still appears • They proved that no life appears if food is sterilized and insulated from the air • i.e. life is not generated spontaneously; it comes from eggs or spores in the air
A second theory: B) A life-force in the air? • Perhaps there’s a ‘life-force’ floating in the air that gets into things and gives them life • How could you test such a theory? How would you test it? Hypothesis testing is a key idea in modern science
Pasteur’s ‘swan-necked’ retort Louis Pasteur: testing the theory of a ‘Life-Force’ • What if a ‘soup’ is boiled in a ‘swan-neck’ retort, and the neck is left open to the ‘life-force’? • Nothing! The contents remain sterile • Conclusion: There is no ‘life force’, and life can only come from life
A third theory: Life came from space! The theory of Panspermia Perhaps living organisms were formed somewhere else And brought into earth by comets and asteroids BUT: how was life made in the first place? www.whitecape.org
But if life can only come from life, how did life first appear? • Solving these puzzles has been one of the great achievements of 20th century biology www.iit.edu/alumni/ upd www.resa.net/ nasa/wq_bio Biology in the 1950s ……………. and the 2010s!
Pt. 2: Modern Accounts of Origins • Many details are still uncertain • But some ideas are clear • Two ideas are fundamental to modern thinking about the origins of life • Spontaneous Generation in modern forms: • Life first appeared in a world without oxygen • Chemical Evolution: • Organic chemicals ‘evolve’ as well as living organisms)
Solving Pasteur’s Paradox: 1) Why oxygen matters • In the early 20th century: • J.B.S. Haldane (in Britain) and A.I. Oparin (in the Soviet Union) argued: • Oxygen is highly destructive of life • Perhaps in an atmosphere without oxygen, life could be generated spontaneously! • Was there oxygen in the first atmosphere? No! Chicago on fire: 1871: Fire reveals the destructive power of Oxygen
2) Chemical Evolution • If simple organic chemicals could form • Perhaps they could slowly change in a form of ‘chemical evolution’ • Getting more and more complicated • Until they created living organisms! • This led to ….. www.icr.org/pubs
A Three-Stage Theory of the Origins of Life • Creating simple organic molecules(amino acids, nucleotides, phospholipids in fats, etc.) 2. Creating organic chemicals that evolve and behave a bit like living organisms (chemical evolution) 3. Creating DNA to control replication (the genetic code)
A) Making the raw materials: The Urey-Miller Experiment • Create a model of the early atmosphere in a flask • Energize it with heat and electric sparks, and wait: • Within 7 days: • a dark red sludge appears, containing many elements from which life is made: • Amino acids (from which proteins are made) • Nucleotides (from which DNA is made) • Phospholipids (from which cell membranes are made) • So: making the raw materials of life is easy if there isn’t too much oxygen around
The tubes are filled with Methane, Ammonia, and Hydrogen Electric sparks are sent through the mixture Within a few days, a dark red sludge appears Water is heated in a flask
Not yet alive! • Tiny organic molecules (only a few tens of atoms in size) • Similar to those in living organisms • BUT today, even the simplest organisms (viruses) have billions of atoms • How do you get from raw materials to living organisms?
Amino acids are simple Proteins are made from chains of amino acids Proteins fold up into complicated balls of matter B) More complex molecules: ‘Chemical evolution’ • Under the right conditions • Organic chemicals link into huge chains of millions of atoms to form proteins andnucleotides
Proteins can form cell-like objects • Under the right conditions: • Protein chains begin to behave like living organisms: • They form round, cell-like balls, with a protective membrane • They take in energy from outside, like simple cells [Metabolism?] • They split in two [Reproduction?] • Over time, they change and evolve [Adaptation? Evolution?] • i.e. large organic molecules are behaving a bit like living organisms: CHEMICAL EVOLUTION
Chains of deep-sea volcanoes Where were conditions right?Near deep-sea volcanoes • Conditions were ideal: • No ultraviolet rays • No meteorite collisions • Heat from the earth’s core • Plenty of water • Plenty of chemicals • Here is where the first life may have formed!
Nearly alive! But not quite! • Now we have complex organic chemicals • Made from the same stuff as living organisms • With metabolism (taking in energy) • Capable of ‘adapting’ (chemical evolution) • They can even reproduce in a fashion • But • They reproduce inaccurately, so they cannot preserve complexity over many generations • The key to life is more accurate reproduction • How do you precisely reproduce something with billions of carefully arranged molecules?
C) The Genetic Code • DNA: the molecule of life • How does it work? • If organisms reproduce too perfectly, adaptation and change are impossible • If they reproduce too imperfectly, they cannot retain the information needed to construct viable organisms • DNA achieves a perfect balance: • Accurate copying • With just a dash of variation
The links: A links with T G links with C Two strands Each group of three links codes for 1amino acid. This group is ‘ACG’ DNA: Basic Structure & Code
The two chains form a spiral Billions of atoms long
Then each strands collects new molecules from its surroundings, making an exact copy of itself (with just a few errors) First, it splits into two strands at the links DNA copies itself
A portion of DNA splits open RNA molecules read off the code Then the strands join up again Decoding DNA: The task of RNA (a relative of DNA with just one strand)
3) Voilà: a new Protein 2) The RNA docks at a ‘ribosome’, which reads the code and makes a new protein 1) An RNA molecule has copied part of the code Then RNA makes new proteins
How Did DNA Evolve? • The most difficult thing to explain • DNA cannot survive on its own • But its close relative, RNA, can • So • RNA may have controlled reproduction in the earliest species • And DNA evolved later as a specialist in preserving the genetic code • At present, exactly how DNA evolved is unclear
Life • So far we’ve tried to • define life • figure out how it works and changes • figure out how it was first created • Now, • how did it change over 3.5 billion years • to create • all the variety of organisms on earth today • organisms of great complexity • including US!
Increasing Complexity • Today, • most organisms are simple • but some are very complex • because we are complex, those are the ones that most interest us • Increasing Complexity means • new energy sources • new ways of relating to the environment • new structures
Part 3: A brief history of life on Earth: Increasing complexity • 8 stages in the history of life on earth • 1. First organisms • 2. Photosynthesis • 3. Prokaryotes Eukaryotes • 4. Sexual reproduction • 5. Multi-celled organisms • 6. Living on the land • 7. Vertebrates • 8. Mammals
DNA but no nucleus 1. The earliest living organisms on earth were ... • Prokaryotes • Too small to be seen with the naked eye • No nucleus: genes float freely inside
Bacteria are prokaryotes 100,000 of these cells could fit in the dot made by a pencil
1. Where did the first organisms get their energy? • From the heat of under-sea volcanoes • And the chemicals that bubbled out of them (like ‘archaebacteria’ today) www.ftns.wau.nl Undersea volcanic eruption near Hawaii
2. Photosynthesis: the first energy revolution • Some organisms rose to the surface of the seas • And learnt to extract the energy of sunlight throughPHOTOSYNTHESIS (like plants today)
What photosynthesis does Carbohydrates store energy for living organisms Plants pump oxygen into the air Plants suck Carbon dioxide out of the air
Why plants are green Chlorophyll is green, and is present in all plants Chlorophyll molecules are where photosynthesis occurs
Photosynthesis allowed life to flourish, spread, and change • Life could now flourish near the surface of the seas • Life had much more energy available, so • living things could spread and evolve more rapidly • living things could become more complex
The oldest fossil bacteria are about 3.5 billion years old They seem to be photosynthesizers, like ‘cyanobacteria’ today
Cyanobacteria: ‘blue-greenalgae’ This fossil of a ‘cyanobacterium’ comes from N. Australia. It is about 1 billion years old. Below is a living relative
STROMATOLITES Cyanobacteria created mushroom-like ‘Stromatolites’ near the surface of early seas. They are huge colonies of dead and living cyanobacteria Cyanobacteria emitted oxygen, and began changing the atmosphere.
3. A second ‘energy revolution’: ‘breathing’ oxygen • The oxygen produced by photosynthesizers was poisonous for most species • Eventually, some bacteria learnt to exploit the exceptional chemical energy of oxygen • Those that could use oxygen flourished and became more complex: • The first ‘eukaryotes’ • They used the energy from oxygen and/or sunlight • Their genes were protected inside the nucleus • They were much larger and more complex than prokaryotes
The nucleus protects the cell’s DNA Mitochondria generate energy from oxygen Eukaryotes (10 – 100 times as large as prokaryotes)
4. Sex! What was bacterial sex like? • For most prokaryotes it was boring: they just cloned • But some eukaryotes began to swap genes before reproducing. Result? • Their offspring were more varied • Greater variety accelerated the pace of evolutionary change
From 600 Million Years ago: The era of multi-celled organisms • Until recently, none of this early history was known • The earliest fossils were thought to have been from the ‘Cambrian’ era, c. 600 million years ago • We now know that this date marks the appearance, not of life, but of the first multi-celled organisms
