History of LifeHistory of Life

Ch t 14Chapter 14

Biogenesis: Living things come from other living thingsliving things.

Li i thi iSpontaneous generation: Living things arise from nonliving things.

Redi’s ExperimentRedi s Experiment

• Francesco Redi (1626-1697) noticed and d ib d th diff t d l t l fdescribed the different developmental forms of flies.Ti lik t t d i t t d• Tiny wormlike maggots turned into sturdy oval cases, from which flies eventually emergedemerged.

D fli t t l f ttiDo flies generate spontaneously from rotting meat?

• Redi’s experimental group consisted of netting-covered jars that contained meat.

• The control group consisted of uncovered jars that also contained meat.j

• What was the purpose of the netting-covered jars?Aft f d t li i i th• After a few days, maggots were living in the meat in the open jars. The net-covered jars remained maggot free.

• The experiment showed that flies come only from eggs laid by other flies.

• What did this do to the theory of• What did this do to the theory of spontaneous generation?

Spallanzani’s ExperimentSpallanzani s Experiment• Many investigators concluded thatMany investigators concluded that

microorganisms arise spontaneously from a “vital force” in the air.

• Spallanzani (1729-1799) designed an experiment to test the hypothesis of spontaneous generation of microorganisms.

• He hypothesized that microorganisms f d f i b f hformed not from air but from other microorganisms.

• For his experimental group, he boiled clear, fresh broth until the flasks filled with steamfresh broth until the flasks filled with steam.

• While the broth was hot, he sealed the flasks by melting their glass necks.by melting their glass necks.

• The control-group flasks of broth were left open.p

• The broth in the sealed flasks remained clear and free of microorganisms.g

• The broth in the open flasks became cloudy because it became contaminated with microorganisms.

• His opponents disagreed with his conclusionconclusion.

• They claimed that he had heated the experimental flasks too long destroying theexperimental flasks too long, destroying the “vital force” in the air inside them.

• Air lacking “vital force” could not generateAir lacking vital force could not generate life.

Pasteur’s ExperimentPasteur s Experiment• Louis Pasteur (1822-1895) won a prize ( ) p

clearing up the issue over spontaneous generation.T k S ll i’ l l• Took Spallanzani’s up one level.

• He made a curve-necked flask that allowed the air inside the flask to mix with the airthe air inside the flask to mix with the air outside the flask.

• The curve of the neck prevented solid e cu e o t e ec p e e ted so dparticles, such as microorganisms, from entering the body of the flask.

• Broth boiled inside the experimental flasks remained clear for up to one year.p y

• He then broke off the curved neck. The broth now became cloudy and contaminated with ymicroorganisms within a day.

Earth’s History: FormationEarth s History: Formation

• 5 billion years ago, our solar system was a5 billion years ago, our solar system was a swirling mass of gas and dust.

• Most of the material was pulled together by p g ygravity and formed the sun.

• The remaining gas, dust, and debris circled g g , ,the sun forming the planets.

Earth’s History: AgeEarth s History: Age

E th i b t 4 5 billi ld• Earth is about 4.5 billion years old.• Early estimates of its age were made by

studying layers of sedimentary rock instudying layers of sedimentary rock in earth’s crust.

Radiometric DatingRadiometric Dating

Method of determining the absolute age of anMethod of determining the absolute age of an object by comparing the relative percentages of a radioactive (parent) isotope and a stable (daughter) isotope.

Isotope: atoms of the same element that differ in the number of neutrons.

The mass number of an isotope is the ptotal number of protons and neutrons in the nucleus.

Radioactive decay: isotopes having unstableRadioactive decay: isotopes having unstable nuclei release particles or radiant energy, or both, until the nuclei become stable. Known as radioactive isotopes.

Half-life: time it takes for one-half of any size sample of an isotope to decay to a stable form. Range from a fraction of a second to billions of yearsbillions of years.

Carbon DatingOrganic materials can be dated by comparingOrganic materials can be dated by comparing

the amount of Carbon-14 (radioactive isotope) with the amount of Carbon-12isotope) with the amount of Carbon 12 (stable isotope). Its half-life is 5,730 years.

Living things take carbon in their bodies constantly. Most is C-12 but a small yproportion of C-14 is also taken in. When an organism dies, its uptake of carbon stops,

d d f C 14 ti Aft 5 730and decay of C-14 continues. After 5,730 yrs., half the C-14 in a sample will have decayed After another 5 730yrs anotherdecayed. After another 5,730yrs., another half will have decayed.

Other isotopes used in radiometric dating:I t H lf lifIsotope Half-lifeUranium-235 704,000,000Potassium-40 1,250,000,000Uranium-238 4,500,000,000

Earth’s age has been estimated based on the decay of uranium and thorium isotopes in rock crystalscrystals.

First Organic Compoundsg p• How were the elements found on Earth and the

rest of the solar system assembled into organicrest of the solar system assembled into organic compounds?

• Hypothesis formed by Alexander Oparin (1894-• Hypothesis formed by Alexander Oparin (1894-1980) and John Haldane (1902-1964).

• Thought that the early atmosphere containedThought that the early atmosphere contained.NH3 – ammoniaH hydrogen gasH2 – hydrogen gasH2O – water vapor

and compounds made of H and C; CH methaneand compounds made of H and C; CH4 - methane

• High temperatures caused the gases to formHigh temperatures caused the gases to form simple organic compounds.

• The cooling of the Earth caused there Amino acids

gcompounds to collect in the waters.

• Lightning and UV radiation may have caused g g ythese compounds to become more complex, resulting in macromolecules.

Cell-like StructuresCell like Structures

• Formed spontaneously in the laboratory fromFormed spontaneously in the laboratory from solutions of simple organic chemicals.

2 types:yp1. microspheres: spherical in shape

and composed of many protein molecules p y pthat are organized as a membrane.

2. coacervates: collections of droplets that are composed of molecules of different types, including lipids, amino acids, and sugars.

Microsphere vs. CoacervatesMicrosphere vs. Coacervates

Microspheres CoacervatesMicrospheres CoacervatesAble to take up certain substances from their

environment.Bud to form smaller microspheres can grow

Both do not have hereditary characteristics.C t d t t l l tiCannot respond to natural selection

The First Life-FormsThe First Life Forms

Thomas Cech (1947- ) found that a type of RNAThomas Cech (1947 ) found that a type of RNA found in certain unicellular eukaryotes is able to act as a chemical catalyst.

Ribozyme: RNA molecule that can act as a catalyst and promote specific chemical reaction.

Supports the hypothesis that life started withSupports the hypothesis that life started with self-replicating molecules of RNA.

The first cells were probably anaerobicThe first cells were probably anaerobic, heterotrophic prokaryotes.

The first autotrophs did not depend on photosynthesis the way most autotrophs

Chemosynthesis: CO2 serves as a carbon

photosynthesis the way most autotrophs do today.

Chemosynthesis: CO2 serves as a carbon source for the assembly of organic molecules. Energy is obtained from the oxidation of various inorganic substances, such as sulfur. Ex: Archae

The First EukaryotesThe First Eukaryotes

Endosymbiosis: a mutually beneficialEndosymbiosis: a mutually beneficial relationship in which one organism lives within another.

Aerobic prokaryotes evolved into modernMitochondria.

Photosynthetic cyanobacteria may have evolved into Chloroplasts.