Evolution: Origin of LifeBiogenesis vs. Spontaneous Generation

Earth’s History

Biogenesis vs. Spontaneous GenerationDefinition: All living

(biotic) things come from other living things.

Common sense today, not believed in the 17th century.

Experiments conducted to prove biogenesis.

Definition: Living things can arise (come from)nonliving (abiotic) things.

Observations that supported the belief: Maggots appeared on rotting meat, fish appeared in seasonal ponds.

Francesco Redi - 1668Addressed maggots appearing on meat.Initial observation: Maggots appear on meat after

flies have landed.Hypothesis: Maggots come from flies NOT meat.Experiment: Placed meat in an open jar and in a

jar that was covered with cheese cloth. Control Group

Experimental Group

More Proof Needed…Microscope was invented around same time

as Redi’s experiment.Scientists began observing ‘tiny creatures’.Accepted Redi’s conclusion but not for

microscopic organisms.Believed microorganisms arise spontaneously

from a “vital force” in the air.

Lazzaro Spallanzani(1729 -1799) Initial observation: Microorganisms grow

easily in food.Hypothesis: Microorganisms formed not from

air but from other microorganisms.Experiment: Placed broth in two flasks,

boiled broth, one flask left open, the other sealed closed.

Control Group:

Experimental Group:

Still not convinced…..Spallanzani concluded that the boiled broth

became contaminated only when microorganisms from the air entered the flask.

Opponents objected to his method and disregarded his conclusion.

Opponents claimed that Spallanzani had heated the flasks too long and destroyed the “vital force” in the air inside the flasks.

Belief in spontaneous generation continued for another 100 years. Until………

Controversy grows Fierce!By mid-1800’s the arguments over S.G. were

fierce.Paris Academy of Science offered a prize

(equivalent to $1 million today) to anyone who could clear up the issue once and for all.

The winner: Louis Pasteur.Why is that name familiar to you?

Pasteur’s ExperimentObservations and hypothesis were the same as

Spallanzani’s.To answer the objections to Spallanzani’s

experiment, Pasteur made a curve-necked flask.Air from outside can mix with inside.Curve in the neck prevented solid particles,

such as microorganisms, from entering the body of the flask with the broth.

Finally, BIOGENESIS became a cornerstone of biology.

Earth’s History

Formation of EarthEarth is believed to be 4.56 billion years old.Earth took 400 million years to form from

gas, dust and debris circling the sun. Earth grew as it was bombarded with debris.Each collision released enough energy to

melt the surface of the forming planet.Estimates of Earth’s age made from studying

layers of sediment in the crust.Accurate estimate through radioactive

dating.

Radioactive (Radiometric) DatingIsotopes: atoms of the same element (same

atomic number or number of protons) but differ in number of neutrons.

Mass number = protons + neutronsIs0topes are designated by chemical name

followed by their mass number. Example: carbon -12 and carbon- 14.Radioactive Decay: isotopes with unstable

nuclei (protons and neutrons in center) tend to release particles or radiate energy (decay)

Radioactive Dating cont.Rates of decay of many radioactive isotopes

have been determined.Half-life: the length of time it takes for ½ of any

size sample of an isotope to decay.Can range from fraction of a second to billions of

years but is specific to each isotope.Age of material is determined by measuring

amount of a particular radioactive isotope it contains and comparing it to the amount of some other substance in the sample that remains constant.

Radioactive Dating cont.http://science.discovery.com/videos/100-great

est-discoveries-shorts-radiometric-dating.html

If the history of the earth were condensed to a 24 hour clock, how long have humans been on the planet?

First Organic CompoundsAll elements found in organic compounds are

thought to have existed on Earth and in the rest of the Solar System when Earth formed.

How and where did these elements assemble into organic compounds found in life?

Oparin hypothesized in 1923, Urey and Miller experimented in 1953 to test Oparin’s hypothesis.

http://science.discovery.com/videos/100-greatest-discoveries-shorts-origin-of-life.html

The first cells.Little to no oxygen gas when they first arose

so…….The first cells were anaerobic.Small size of the oldest microfossils indicate

the first cells were prokaryotes (no nucleus).First cells were heterotrophs, consuming

organic molecules from their environment.Autotrophs evolved due to strong pressure in

the environment (competition for food).First autotrophs performed chemosynthesis.

Photosynthesis and Aerobic RespirationPhotosynthesizing autotrophs evolved and put

oxygen into the atmosphere (around 3.5 billion years ago).

Took billions of years for oxygen gas to reach today’s levels.

Oxygen was dangerous to many early organisms because it could destroy coenzymes essential to cell function.

Oxygen bonded to other compounds in some organisms, preventing damage, this was the first step to aerobic respiration.

The first eukaryotes.2 to 1.5 billion years ago.Small aerobic prokaryote entered and began to

live and reproduce inside larger, anaerobic prokaryotes.

Mutually beneficial relationship – endosymbiosisSmall aerobic prokaryote = today’s

mitochondria (remember they have their own DNA)

Similar situation for chloroplast in photosynthetic cells.

http://videos.howstuffworks.com/discovery/29535-assignment-discovery-prokaryotes-the-first-cells-video.htm