copyright cmassengale Origin of Life copyright cmassengale

copyright cmassengale Example #1 Observation: Every year in the spring, the Nile River flooded areas of Egypt along the river, leaving behind nutrient-rich mud that enabled the people to grow that year’s crop of food. However, along with the muddy soil, large numbers of frogs appeared that weren’t around in drier times copyright cmassengale

copyright cmassengale Example #1 Conclusion: It was perfectly obvious to people back then that muddy soil gave rise to the frogs copyright cmassengale

copyright cmassengale Example #2 Observation: In many parts of Europe, medieval farmers stored grain in barns with thatched roofs (like Shakespeare’s house). As a roof aged, it was not uncommon for it to start leaking. This could lead to spoiled or moldy grain, and of course there were lots of mice around. copyright cmassengale

copyright cmassengale Example #2 Conclusion: It was obvious to them that the mice came from the moldy grain. copyright cmassengale

copyright cmassengale Example #3 Observation: In the cities centuries ago, there were no sewers, no garbage trucks, no electricity, and no refrigeration. Sewage flowed down the streets, and chamber pots and left over food were thrown out into the streets each morning. Many cities also had major rat problems and a disease called Bubonic plague. copyright cmassengale

copyright cmassengale Example #3 Conclusion: Obviously, all the sewage and garbage turned into the rats. copyright cmassengale

copyright cmassengale Example #4 Observation: Since there were no refrigerators, the mandatory, daily trip to the butcher shop, especially in summer, meant battling the flies around the carcasses. Typically, carcasses were “hung by their heels,” and customers selected which chunk the butcher would carve off for them. copyright cmassengale

copyright cmassengale Example #4 Conclusion: Obviously, the rotting meat that had been hanging in the sun all day was the source of the flies. copyright cmassengale

copyright cmassengale Abiogenesis Recipes Recipe for bees: Kill a young bull, and bury it in an upright position so that its horns protrude from the ground. After a month, a swarm of bees will fly out of the corpse. copyright cmassengale

copyright cmassengale Abiogenesis Recipes Recipe for mice: Place a dirty shirt or some rags in an open pot or barrel containing a few grains of wheat or some wheat bran, and in 21 days, mice will appear. There will be adult males and females present, and they will be capable of mating and reproducing more mice. copyright cmassengale

The idea that life can emerge from non-living material is called abiogenesis or spontaneous generation. This idea is first credited to Aristotle, but was widely believed for about 2000 years. The idea lasted so long because people based their beliefs on observations and they did not test them.

copyright cmassengale

Spontaneous Generation For centuries, people based their beliefs on their interpretations of what they saw going on in the world around them without testing their ideas They didn’t use the scientific method to arrive at answers to their questions Their conclusions were based on untested observations copyright cmassengale

Disproving Spontaneous Generation copyright cmassengale

copyright cmassengale Francesco Redi (1668) Francesco Redi was an early scientist who conducted experiments to try and disprove spontaneous generation. copyright cmassengale

copyright cmassengale Redi’s Experiment His hypothesis was that rotten meat does not turn into flies; they come from other flies. Redi used open & closed flasks which contained rotting meat. He observed these flasks to see in which one(s) maggots would develop. copyright cmassengale

Redi’s (1626-1697) Experiments Evidence against spontaneous generation: 1. Unsealed – maggots on meat 2. Sealed – no maggots on meat 3. Gauze – few maggots on gauze, none on meat copyright cmassengale

copyright cmassengale Redi’s Findings He found that if a flask was closed with a lid so adult flies could not get in, no maggots developed on the rotting meat within. In a flask without a lid, maggots soon were seen in the meat because adult flies had laid eggs and more adult flies soon appeared. copyright cmassengale

Results of Redi’s Experiments The results of this experiment disproved the idea of spontaneous generation for larger organisms, but people still thought microscopic organisms like algae or bacteria could arise that way. copyright cmassengale

copyright cmassengale Francesco Redi copyright cmassengale

Did Redi Use the Scientific Method? copyright cmassengale

copyright cmassengale The Scientific Method Observation Hypothesis Experiment Accept, Reject, or Modify hypothesis copyright cmassengale

copyright cmassengale Step 1 - Observation There were flies around meat carcasses at the Butcher shop. Where do the flies come from? Does rotting meat turn into or produce rotting flies? copyright cmassengale

copyright cmassengale Step 2 - Hypothesis Rotten meat does not turn into flies. Only flies can make more flies. copyright cmassengale

copyright cmassengale Step 3 - Testing Wide-mouth jars each containing a piece of meat were subjected to several variations of “openness” while all other variables were kept the same. Control group — These jars of meat were set out without lids so the meat would be exposed to whatever it might be in the butcher shop. Experimental group(s) — One group of jars were sealed with lids, and another group of jars had gauze placed over them. copyright cmassengale

copyright cmassengale Step 4 - Data Presence or absence of flies and maggots observed in each jar was recorded. Control group – flies entered, laid eggs, & maggots emerged Gauze covered – flies on gauze, but not in jar Sealed jars – No maggots or flies on the meat copyright cmassengale

copyright cmassengale Step 5 - Conclusion Only flies can make more flies. In the uncovered jars, flies entered and laid eggs on the meat. Maggots hatched from these eggs and grew into more adult flies. Adult flies laid eggs on the gauze on the gauze-covered jars. These eggs or the maggots from them dropped through the gauze onto the meat. In the sealed jars, no flies, maggots, nor eggs could enter, thus none were seen in those jars. Maggots arose only where flies were able to lay eggs. This experiment disproved the idea of spontaneous generation for larger organisms. copyright cmassengale

Disproving Spontaneous Generation of Microbes copyright cmassengale

After development of the microscope people knew of the existence of microbes. Scientists began arguing the idea of spontaneous generation for microorganisms.

Anton van Leeuwenhoek 1632-1723 copyright cmassengale

Anton van Leeuwenhoek (1674) Leeuwenhoek began making and looking through simple microscopes He often made a new microscope for each specimen He examined water and visualized tiny animals, fungi, algae, and single celled protozoa; “animalcules” By end of 19th century, these organisms were called microbes copyright cmassengale

Leeuwenhoek’s Microscope copyright cmassengale

John Needham (1745) John Needham performed tests to support the idea of abiogenesis. He believed there was a “life force” present in non-living material such as air that could give rise to living things.

copyright cmassengale Needham’s Experiment copyright cmassengale

copyright cmassengale Needham’s Results Needham’s experiments seemed to support the idea of spontaneous generation People didn’t realize bacteria were already present in Needham’s soups Needham didn’t boil long enough to kill the microbes copyright cmassengale

Lazzaro Spallanzani (1765) Lazzaro Spallanzani repeated Needham’s experiment making changes he thought would help disprove spontaneous generation.

Lazzaro Spallanzani’s (1765) Boiled soups for almost an hour and sealed containers by melting the slender necks closed. The soups remained clear. Later, he broke the seals & the soups became cloudy with microbes. copyright cmassengale

Spallanzani’s Results copyright cmassengale

copyright cmassengale Conclusion Critics said sealed vials did not allow enough air for organisms to survive and that prolonged heating destroyed “life force” Therefore, spontaneous generation remained the theory of the time copyright cmassengale

The Theory Finally Changes copyright cmassengale

copyright cmassengale How Do Microbes Arise? By 1860, the debate had become so heated that the Paris Academy of Sciences offered a prize for any experiments that would help resolve this conflict copyright cmassengale

The theory finally changed after the experiments of Louis Pasteur The theory finally changed after the experiments of Louis Pasteur. He believed that microbes were carried on dust particles in the air and not by some “life force” in the air itself. The success of Pasteur’s experiment was based on the special design of his flasks. They were designed to let air in, but keep dust out.

copyright cmassengale Louis Pasteur (1822-1895) copyright cmassengale

copyright cmassengale Pasteur's Problem Hypothesis: Microbes come from cells of organisms on dust particles in the air; not the air itself. Pasteur put broth into several special S-shaped flasks Each flask was boiled and placed at various locations copyright cmassengale

Pasteur's Experiment - Step 1 S-shaped Flask Filled with broth The special shaped was intended to trap any dust particles containing bacteria copyright cmassengale

Pasteur's Experiment - Step 2 Flasks boiled Microbes Killed copyright cmassengale

Pasteur's Experiment - Step 3 Flask left at various locations Did not turn cloudy Microbes not found Notice the dust that collected in the neck of the flask copyright cmassengale

Pasteur's Experimental Results copyright cmassengale

The Theory of Biogenesis Pasteur’s S-shaped flask kept microbes out but let air in. Proved microbes only come from other microbes (life from life) - biogenesis copyright cmassengale Figure 1.3

copyright cmassengale Review copyright cmassengale

copyright cmassengale Evidence Pro and Con 1668: Francisco Redi filled jars with decaying meat. Conditions: Results: 3 jars covered No maggots 3 jars covered with fine net Maggots on netting 3 open jars Maggots appeared From where did the maggots come? What was the purpose of the sealed jars? Spontaneous generation or biogenesis? copyright cmassengale

copyright cmassengale Evidence Pro and Con 1745: John Needham put boiled nutrient broth into covered flasks. Conditions: Results: Nutrient broth heated, then placed in sealed flask Microbial growth From where did the microbes come? Spontaneous generation or biogenesis? copyright cmassengale

copyright cmassengale Evidence Pro and Con 1765: Lazzaro Spallanzani boiled nutrient solutions in flasks. Conditions: Results: Nutrient broth placed in flask, heated, then sealed No microbial growth Spontaneous generation or biogenesis? copyright cmassengale

After proving that life can only arise from other living things, people began to question where the first living things came from to set this in motion. While we cannot prove anything, we can use evidence and the scientific method to theorize about how life may have begun on Earth.

The atmosphere of the early earth was very harsh The atmosphere of the early earth was very harsh. It was extremely hot and wet and contained little free _______. It was not a suitable environment for life at the time. oxygen

Some believed that organic molecules could form in the atmospheric gases found in early earth with the help of an energy source such as lightening.

Stanley Miller ___________and Harold Urey (1953) showed experimentally that these gases could react with one another to form small organic molecules. They placed ammonia, methane and hydrogen in a closed container. The mixture was heated and electricity was introduced to simulate lightening and mimic conditions on early Earth. After several days they found organic substances (amino acids, sugars) were present in the mixture.

The development of lipid membranes gave rise to ________, which are membrane-bound organic chemicals that can carry out some sort of metabolism. The first true cells were probably anaerobic prokaryotes and used ____________ to produce their energy protocells chemosynthesis

Cyanobacteria ozone layer _____________, the first photosynthetic prokaryotes are thought to have developed later. Photosynthesis produced enough oxygen to form the ___________ layer which cooled down the earth and protected it from UV rays. ozone layer

Because of the hot conditions of early earth, it is believed that most organisms originated in ________. The formation of the ozone layer would allow for land-dwelling organisms to develop. the ocean

Lynn Margulis (1960’s) theorized that the first eukaryotic cells were formed when prokaryotic cells began forming symbiotic relationships with other prokaryotes.

This relationship may have actually consisted of one prokaryote living inside another, paving way for the development of organelles. This is known as the endosymbiont theory. Mitochondria and chloroplasts both have _____ that is different from the DNA in the nucleus of the cell. Both mitochondria and chloroplasts aid in giving the cell ______. DNA energy

Eukaryotic cells began living together to form colonies that later developed into tissues which paved the way for __________ organisms. ______ reproduction and natural selection have helped create the diversity among species that we see on Earth today. multicellular Sexual

Scientists estimate that the earth is about ____4 Scientists estimate that the earth is about ____4.6 Billion____ years old. The scientists that study ancient life are called paleontologists. About _99_% of species that have lived on earth are now extinct. ___Fossils____ are remains or traces of past life. Fossils help us learn about extinct species and help show similarities between past and present species.

Fossils are formed in _sedimentary_____ rock Fossils are formed in _sedimentary_____ rock. Sedimentation is an accumulation of particles forming __strata____, recognizable layers laid down in sequence on land. The sequence indicates the age of the fossils; a stratum is older than the one above it and younger than the one below it.

___Relative___ dating of a stratum is done by comparing fossils found in strata around the world. Strata of the same age contain the same fossils. This does not establish age of fossils in years, just periods.

___Radiometric____ dating (aka carbon dating) is done to determine the actual age of fossils. Radioactive isotopes have a half-life, the time it takes for half of a radioactive isotope to change into a stable element. Carbon 14 is a radioactive isotope found in organic matter. Half of the carbon 14 will change to nitrogen 14 every 5,730 years. Comparing the carbon 14 radioactivity of a fossil to modern organic matter calculates the age of the fossil.

Scientists have constructed a geological timescale that divides the history of the earth into eras and periods. Life on earth is estimated to have first appeared 3.5-3.9 billion years ago. _Precambrian__ Era-Ended about 550 MYA. Lasted for about 3 billion years. All life was single-celled or cell colonies. ___Paleozoic__Era-Lasted from 500-250 MYA. Invertebrates and vertebrates formed. Fishes, amphibians and reptiles appear. Land plants including seed plants and conifers appear.

_Mesozoic___ Era-From 250-65 MYA. Dinosaurs appear and die out _Mesozoic___ Era-From 250-65 MYA. Dinosaurs appear and die out. Mammals and birds appear. Flowering plants dominate. __Cenozoic___ Era-From 65 MYA till present. Placental mammals appear. Primates (30 MYA) and humans (200,000 YA) appear.