Spallanzani's Experiment: Disproving Spontaneous Generation

Biogenesis vs. Abiogenesis

• Biogenesis states that all living things originate from pre-existing living things.
• Spontaneous generation or abiogenesis, the idea that living things can arise from non-living matter, was believed prior to the 17th century.
• Examples thought to support abiogenesis involved maggots from dead meat, mice from grain, and beetles from dung.

Francesco Redi's Experiment (1668)

• Redi disproved spontaneous generation with an experiment involving rotting meat, maggots, and flies.
• At the time, it was believed maggots and flies spontaneously arose from rotting meat.
• Redi aimed to disprove that flies spontaneously produce maggots from meat.
• The experiment used a control group (open jar) and an experimental group (covered jar).
• The control group allowed meat in a jar to be exposed to flies, resulting in maggots.
• The experimental group had meat covered, preventing flies from accessing it, therefore no maggots formed.
• The cloth allowed air but prevented flies allowing no maggots in covered jars.
• This proved that flies produce maggots.

Lazzaro Spallanzani's Experiment (mid-1700s)

• A microscope was invented when Redi conducted his experiment, revealing microorganisms.
• Many believed microorganisms appeared via spontaneous generation from the air.
• Spallanzani tested the hypothesis about spontaneous generation of microorganisms.
• The hypothesis being tested was microorganisms originate from other organisms, not air.
• Sterilized broths in flasks, one open and one sealed showed this.
• Both flasks were boiled, killing any microorganisms.
• The open flask contaminated the boiled broth but the closed flask did not.
• Spallanzani concluded microorganisms contaminate boiled broth from the air since it was absent in the closed flask, therefore disproving spontaneous generation.
• He was objected to by scientists who still believed in spontaneous generation who claimed he heated the vital force too long, and without new air entering, spontaneous generation was not possible.

Louis Pasteur's Experiment (mid-1800s)

• Pasteur finally disproved spontaneous generation once and for all.
• Broth was boiled killing existing mircoorganisms.
• Over one year passes, and the broth remainded sterilized since the curved neck allowed air, but prevented solid particles containing microorganisms from.
• The broth would become cloudy immediately with microorganisms.
• Those believing in spontaneous generation argued that scientists could not create objects, since vital force prevent it.

Earth's Age and Origin of Life

• Pasteur ended spontaneous generation opening how cell-based life arose on Earth.
• Scientists look to the past for evidence to form and test hypotheses about the origin of life.
• The earth is estimated to be over 4 billion years old.
• Exploring the layers of Earth's surface establishes a picture of its geologic history.
• Early estimation attempts of earth's age from sedementary rock layers proved unsuccessful.
• The mid-20th century gave modern techniques, making more accurate estimates possible.
• Scientists use radioactive and relative dating to determine the age of rocks and fossils.

Radioactive Dating

• Radioactive dating is used to establish the age of rocks and sediments.
• Isotopes of the same element differ in the number of neutrons.
• Elements with isotopes have the same atomic number but different atomic masses.
• Atomic mass is the combined number of protons and neutrons.
• Unstable isotopes undergo radioactive decay and release particles or energy.
• These isotopes exhibiting decay are called radioactive isotopes.
• Half-life defines the time it takes for one-half of an isotope sample to decay.
• The age of a material can be determined by testing the amount of a particular radioactive isotope it contains.

Carbon-14 Dating

• All living things take carbon into their bodies.
• All organisms constantly intake most carbon in the isotope carbon-12 (stable).
• All living things contain small portions of carbon-14 (radioactive isotope that decays).
• The ratio of C-12 to C-14 in living organisms is a known quantity.
• Once an organism dies, it no longer intakes carbon, therefore the C-14 begins to decay and C-12 remains.
• Over time, the amount of C-14 declines relative to C-12.
• The half-life of C-14 is 5,730 years meaning there will only be 50% of original found in a fossil.
• An age estimate of fossiles can be determined by comparing the amount of C-12 to C-14 remaining within fossils.
• There are limits to C-14 dating due to C-14's short half-life, limited to organisms which are less than 75,000 years old.

Dating Older Rocks and Sediments

• Isotopes with longer half-lives are needed to date these.
• Potassium-40 (half-life 1.3 billion years) and Uranium-238 (half-life 4.5 billion years) are two common isotopes used.
• Dating older fossils using these isotopes is challenging since living things do not intake them.
• Dating instead takes place in a mineral layer or strata by measuring the isotopes.
• When a fossil is found in the particular layer, the fossil matches the rock layers relative age.

Relative Dating

• Relative dating determines fossil age by comparing its placement in rock layers relative to fossils in other layers.
• Sedimentary rock layers form in order of age, with the oldest on the bottom and the newest closer to the surface.
• By studying layers of rock strata it can be determined if one fossil is older than another based on it's position.
• Relative dating allows one to estimate a fossil's age compared to that of other fossils.

Relative vs. Absolute Age

• Scientists seek both the relative and absolute age of a fossil.
• A relative age is the age in relation to other objects.
• Fossils in lower strata are deemed older than those found at higher strata.
• Absolute age is the actual age in years of the fossil.
• Absolute age is determined through radioactive dating processes, using radioactive isotopes with a half-life.
• Fossils contain these isotopes, and the material's age is determined by measuring the amount of the isotopes it contains.

Earliest Evidence of Life

• The earliest confirmed evidence of life on Earth comes from microoganism fossils about 3.5 billion years old.
• Scientists hypthesize that chemical and physical processes, aided by natural selection, created very simple cells, through a sequence of 4 stages:
• Abiotic synthesis: The nonliving systhesis of small organic molecules like nucleotides.
• The joining of small molecules into macromolecules proteins and nucleic acids.
• The packaging of these molecules into "protobionts" (droplets with internal chemistry different from their surroundings).
• The origin of self-replicating molecules, eventualy making inheritence possible.

The First Organic Compounds

• The Oparin Hypothesis (1923) was the first to prpose how organic compounds formed on earth.
• Oparin suggested the earlly atmosphere on earth was different than.
• Oparin said the primitive atmosphere contained ammonia, hydrogen gas, water and hydrocarbons.
• Oparin believed high temperatures formed simple organic compounds like amino acids.
• Water vapor condensing formed lakes and seas making simple organic compounds become collected.
• Lightning and UV radiation fueled complex chemical reactions forming macromolecules essential to life like proteins.

Miller-Urey Experiment

• Stanley Millery/Harold Urey set up an experiment to test Oparin's hypothesis in 1953.
• Experiment included a chamber that contained hypothesized gases in the early atmosphere.
• Electrical sparks substituting for lightning supplied energy to derive chemical reactions.
• Demonstrating abiotic synthesis, they experiment proved that the abiotic synthesis of molecules is possible.

New Evidence

• Evidence indicates the early atmosphere may not of included enough ammonia and methane required.
• The primitive atmosphere was composed of mostly (carbon dioxide, nitrogen, and water vapor).
• Both carbon dioxide and oxygen interfere with the production of organic compounds.
• The first organic compounds are currently believed to of formed around deep-sea hydrothermal vents where conditions favor complex reactions.
• Vent regions being rich in sulfur and iron compounds favoring organic conditions.

Molecules to Cell Structures

• Simple cell structures form spontaneously in labs from solutions of simple chemicals.
• These structures include "microspheres" and "coacervates."
• Microspheres are spherical and are made of many protein molecules in a membrane.
• Caocervates are droplet collections of various molecules (including linked amino acids and sugars).
• Small organic monomers are insufficient.
• A vast assortment of macromolecules drives self replicating.
• Sydney Fox in the 1960s synthesized organic polymers by dripping organic monomer solutions over hot sand, clay, or rock which vaporized the water encouraging polymerization.
• Microspheres and coacervates have some similar properties of life, with the ability to intake, and grow.
• All can bud to form smaller microspheres.
• Since the previous processes can arise without genes, they can not be considered "alive".

The First Life Forms

• The two key properties of all life are accurate replication and metabolism.
• The necessary properties may have been found in photobionts.
• Protobionts are collections of molecules (microspheres) surrounded by a membrane structure.
• They show simple reproduction and metabolism, plus maintenance of their internal chemical environment.
• Protobionts may have been precursors to prokaryotic cells.

Origin of Heredity

• RNA was likely the first genetic material, not DNA.
• RNA can take on a greater variety of shapes than DNA caused by hydrogen bonding between particular nucleotides, just as the shapes of proteins come from amino acids.
• RNA some molecules behave like proteins and can catalyze.
• RNA molecules with these properties of catalyst were discovered and being called "ribozyme".
• Ribozyme helps RNA act as enzyme and create chemical reactions.
• Ribozymes helping RNA act as template, can replicate itself.
• Studies indicate the molecules would have heredity and be able to act to natural selection.
• Competetition between RNA molecules takes places to intake a fixed number of nucleotides and successful molecules in obtaining them has an advantage to offspring.
• The RNA molecule whose with sequence best suited can replicate itself can leave the most decendent.
• These descendants will not be identical and occasionally are able to evolve better, then replicating.
• These would then be passed on to the offspring inside protobionts, which then could evolve into regular cells.
• That RNA would then provide would have provided the heredity information.

The Fossil Record and History of Life

• The fossil record shows the evolution of life over its billions of years.
• The types of organisms have greatly changed throughout time.
• Most fossilized ancient organisms were unlike today's organisms, many which are now extinct.
• Fossils show how new groups of organisms formed through previously existance.
• The fossil record is an incomplete record.
• Many organisms did not die correctly to be preserved and thus die without tracd.
• Many fossils have been geologyically destroyed.
• Only a minor part of those which existed are found.
• As a result the fossil record contains the long lived organisms which can survive widespread enviroments and create shells. from organisms.
• From fossils, scientists created geologic records highlighting major events.

First Single-Celled Organisms

• The first organisms had little to no free oxygen, therefore the cells must have been anaerobic.
• The oldest microfossils were prokaryotes and most likely heterotrophs.
• Autotrophs were likely chemosynthetic.
• Carbondioxide is utilized as carbon for built organic molecules.
• Energy for the process comes from inorganic chemical reactions.
• These prokarotes were the only inhabitants with the oldest believed to be 3.5 billion years old.
• The archaebacteria alive on Earth is the only bacteria that mirrors these ancient organisms.
• These archaebacteria thrive in extreme anaerobic conditions.
• Some cells were able to manufacture their own organic compunds (sugars) using carbon dioxide and the sun which drives chemical reactions.
• A very damaging byproduct formed, oxygen.
• Oxygen inhbited some enzymes and damaged cells.
• The rising oxygen allowed for photosynthesis, probabaly doomed groups of organisms since oxygen kills anaerobic cells.
• Some species had adaptions to survive, such as cellular respation (using O2) for energy and Cyanobacteria's photosynthesis.

It Took Oxygen a Billion Yrs

• It took over a billion years for the right concetration for todays levels to be formed.
• After the oxygen reached upper atmosphere, it reacted to Sunlight.
• Sunlights splits the radiation to O2 to split and form one O atom.
• These O atoms react with O2 again to form ozone (O3).
• Ozone absorbs radiation preventing life from dying.
• This radiation helps protect the DNA.
• Without the important layer of ozone, no earth organism could live.

First Eukaryotes

• Eukaryotic cells differ from prokaryotic cells.
• Eukaryotic cells are larger in comparison.
• DNA is organized into individual chromosomes housed in a cell's nucleolus.
• Contain membranous organelles, plus cytoskeletons.
• After 2-1.5 billion years ago, a type of small aerobic prokrayote entered and reprouced inside larger, anaerobic organisms.
• This type of invasion may evolved into a mutually beneficial relationship.
• The theory helps make organisms able to eventualy turn into modern mitochondria through its resiparation.
• After there was another successful invasion of pre-eukaryotic cells, this time by modern photosynthetic cyanobacteria.
• The new invaders made way, with the development of the chloroplast to allow for photosynthesis.
• To confirm the previous, one can look at one of the two examples with bacteria.
• Some orgamisms that have cloroplasts and mitoctondria replicate independently.
• Cloroplast and mito have they own DNA different by the nuclei but consist in the same circular strand.
• The mito and chloro have own synthesis that prokayotic do not have.
• Contains the same membinarous enzyme to prokartote.

Sexual Reproduction and Evolution

• Most prokaryotic cells reprodue asexualy which divides into two indentical cells without mutation.
• After the eukaryotic cells appeared, the cells sexually reprodue and allowed for genetics to exist.
• Allows the parent contributions of half the chromosomes each for the offspring.
• Due to a large number of gene combinations and better chance of traits to be shown for the offering, allows natural selesction and evolutinary change.
• the development of secual reproduction caused a greater chance in the appearing of new species at large scales.
• A few hundred million years after repdouction, there was even further innovation with multicellular organisms.

First Multi Eukaryotes

• After the earlist eukaryotic, many species evolved and continued today.
• Sme gave rise to multicellular and included algae, fungi, planets, or animals.
• Some of the oldests fossils used to be small algar around 1.2 billion years ago.
• The fossil records had diverse multicellural ogranisms but after 565 billion years ago that cambrain explostion.
• during 535-525 millions ago, there were many animals in phlya that suddenly were found.
• Beforehand only 3 animals are found mostly spogies.
• All these early were soft-bodied, not predation.

Colonization and Land

• Fungi, Planet, and Animals began and colonoized.
• the two problem of reproducing out of water helps create more selesction for certain animals.
• The planets today, contain soloutions for these problems.
• they contain vestular tissure like pholem and xylem.
• the plants created waxy coating that prevents water lost.
• all the plants deliver the egg though spores that carry by the air.
• one adaptation of the plants has animals create a exoskeketon with the plants themself.
• The animals create a amnite egg with the shell.

Life Processes

• life can rise and fall based on how the animals exist to rise to.
• Continental Drifts change and move and it can change how a organims can adapt
• there will be more continents that exist and more that create more oppotunies.
• some of the climate creates a change too.
• fossil records exist with other with the majority animals being extinit, for they could not have been more adaptibe since an envoriotnment.
• or destroyed
• the 5 mass estinctions had destroyed what they know.
• adptive radations had great evoltuionary change.
• Some animals evolved where other may have lived, with new niches.
• the new organims can fill in the other comuntities that the aniamls can be in to allow them to adapt.

Explore Spallanzani's experiment and its impact on disproving spontaneous generation. Understand the key observations, experimental setup, and criticisms of his work. Learn about the role of boiling and the significance of filtered air in the debate.