Origin of Life on Earth Biology CP Source: Biology, The Dynamics of Life. Glencoe/McGraw-Hill, 2002.

Early Ideas about Origins of Life Spontaneous generation - life arising from nonliving matter Examples: mud producing fish grain producing mice decaying meat producing maggots

Redi’s Experiment Effort to disprove spontaneous generation Decaying meat in uncovered control jars vs. covered experimental jars. Results?

Redi’s Experiment Effort to disprove spontaneous generation Decaying meat in uncovered control jars vs. covered experimental jars. Results: maggots and flies filled the open jars but not covered jars. Showed only flies produce flies.

People still didn’t believe it… Although Redi disproved spontaneous generation of large organisms, many scientists thought microorganisms must arise spontaneously, probably from a vital force in the air.

Pasteur’s Experiment (mid-1800s)

Ideas about Origins of Life Biogenesis-life arising from other organisms Where did the first life come from?

First Things First: Before we talk about the origin of life we must talk about the origin of: Universe Earth’s Oceans Earth’s Atmosphere Earth’s Crust

Big Bang Theory Explains how the universe formed-13.7 bya Universe began as an infinitely small, hot dense ‘speck’ that inflated, expanded and cooled to the size and temperature of our current universe. Earth formed 4.5-4.6 bya

Formation of the Oceans Tremendous amounts of hydrogen and oxygen were trapped below the crust combined to form water vapor, which was released to the atmosphere The water vapor condensed in the atmosphere and rained down to form vast oceans

Earth’s Early Atmosphere Compound Elements Present Molecular Formula methane carbon, hydrogen CH4 ammonia nitrogen, hydrogen NH3 hydrogen H2 water hydrogen, oxygen H2O carbon dioxide carbon, oxygen CO2

Sequence of conditions on primitive earth Heavy particles such as iron, copper and nickel were pulled to the center of the earth. Lighter particles such as helium and hydrogen remained at the surface.

Sequence of conditions on primitive earth: Radioactive material and great pressure kept the center of the earth in a molten state. Over a period of years, the outer surface or crust of the earth formed over the molten center (4 billion years ago As the outside of the earth cooled, hot gasses from the interior escaped to form the primitive atmosphere

What major gas, necessary for life, is missing from the atmosphere of primitive Earth?

Primitive Earth’s Atmosphere Primitive Earth set the stage for the formation of organic molecules This could not have happened on Modern Earth!

Why are organic molecules important to the origin of life? Organization of simple organic molecules lead to more complex organic molecules such as proteins, carbohydrates, and nucleic acids. More complex organic molecules lead to cells = LIFE.

Earth’s Early Atmosphere Oxygen (O2) - a highly reactive compound. Will break bonds that form between simple organic compounds and destroy them. Primitive atmosphere lacked free Oxygen (O2): simple organic compounds could form and remain stable even when exposed to air

Energy used to join atoms that form hydrocarbons ! Forms of Energy on primitive Earth UV Radiation (no Ozone layer to block it) lightning in the atmosphere heat from volcanoes above and below ocean level

Primtive Earth

Theory of Chemical Evolution In 1924, Alexander Oparin and J. B. Haldane developed a theory for the origin of organic compounds Conditions on primitive earth gave rise to simple organic compounds, the precursors to life

Theory of Chemical Evolution Inorganic Matter- (like CO2 & NH3) plus organic molecules (CH4) in the atmosphere combined using energy Simple Organic Molecules – like HCN (hydrogen cyanide) and formaldehyde formed primitive clumps of organic matter.

Miller and Urey (1953) In 1953, Stanley Miller and Harold Urey developed a model to test the Oparin/Haldane Hypothesis Set up a simulation of conditions on early earth…guess what they found…

Miller and Urey (1953) Gasses in the apparatus:CH4, CH3, H2O, H2 Source of energy: electricity And after 1 week…. Analysis of substances (“organic soup”) collected in the trap: HCN (hydrogen cyanide), lactic acid, acetic acid, simple amino acids, formaldehyde

What would happen if you add O2 to the above mixture? reduces the amounts of organic molecules formed or eliminates them because oxygen gas is highly reactive!

Other scientists used UV light in this model and formed… Simple organic molecules like HCN which can be used to form adenine, a nitrogen base… Importance? Formation of Nucleic Acids- DNA, RNA

The Heterotroph Hypothesis Once simple, organic compounds were formed, polymers of carbohydrates, proteins, lipids and nucleic acids are formed….HOW?

How did simple organic molecules form complex organic molecules? Studies in 1950’s showed that if amino acids are heated without oxygen, they form proteins. A similar process produces ATP and nucleic acids from small molecules. Therefore, this may have occurred on early earth in the warm pools of water.

Formation of Life Complex organic molecules can form primitive cells= LIFE! Protocells, simple precursors to cells then evolved into primitive cells with RNA as the genetic material:

Origin of Life simple organic compounds  polymers  protocells  primitive cells

How did these molecules become CELLS? Sidney Fox: Protocells could be formed by heating solutions of amino acids. Protocell is a large, ordered structure, enclosed by a membrane, that carries out some life activities, such as growth and division.

Were the primitive cells Heterotrophs?-organism which requires an external supply of energy in the form of food as it cannot synthesize its own Autotrophs?-is an organism that produces complex organic compounds from simple inorganic molecules using energy from light (by photosynthesis) or inorganic chemical reactions.

Which form of life is a simpler design? Heterotrophs! Why? Autotrophs have to make glucose (high energy organic molecules) which requires A LOT more enzymes and extra genes (DNA) Plus Autotrophs have to convert glucose just like heterotrophs (go through same reactions)

Which form of cellular respiration was used? Aerobic (uses O2) OR anaerobic (no O2 used) Answer: anaerobic respiration (fermentation) Anaerobic heterotrophs consumed organic matter (organic “soup”) and underwent anaerobic respiration The first Autotrophs: 2.5 bya – primitive cyanobacteria Example: blue green algae

The first Autotrophs: 2.5 bya – primitive cyanobacteria Example: blue green algae

Photosynthesis provided two important things source of food for heterotrophs and 2) free O2 for the environment & aerobic (uses O2) respiration

The effect of photosynthesis on development of the ozone layer 1)  Some of the O2 formed by producers is used to form the ozone layer: O2 + UV light  O3 2)  Ozone blocks most Ultraviolet radiation from reaching the Earth. 3)  One source of energy for formation of organic compounds is reduced BUT, 4) Organisms exposed to the atmosphere are not harmed by the UV radiation. 5) O2 becomes available for aerobic cellular respiration

The effect of photosynthesis on development of the ozone layer

~LIFE BEGAN!~ We have found fossils of photosynthetic prokaryotic cells from 3.5 billion years ago. However, these were probably not the first cells.

~LIFE BEGAN!~ We have found fossils of photosynthetic prokaryotic cells from 3.5 billion years ago. However, these were probably not the first cells. Reminder: prokaryotic: simple cell structure, no nucleus example: bacteria eukaryotic:complex cell structure, has nucleus examples: protists, fungi, plants, animals

The First Cells First cells were probably prokaryotes that evolved from protocells; didn’t need oxygen, used molecules in oceans for food. At some point, some cells developed the ability to make their own food CHEMOSYNTHESIS - making glucose from inorganic molecules, probably near deep sea vents or in hot springs. No light needed.

And later... Some cells developed the ability use light to perform PHOTOSYNTHESIS. This started increasing the amount of oxygen in the atmosphere. Some cells developed the ability to use oxygen through respiration. Lightning caused some oxygen (O2) to form ozone (O3). Protective layer, prevents most UV radiation from sun stopped origin of cells; enabled evolution of more complex cells.

Evolution of Eukaryotic Cells Lynn Margulis (1960s) - Endosymbiont Theory Ancient bacteria may have “taken in” other bacteria, which evolved to become cell structures such as mitochondria and chloroplasts. Supporting Evidence: M & C have their own DNA (similar to prokaryotes) M & C have ribosomes (similar to prokaryotes) M & C reproduce independently within cells

And finally... Over millions of years, these early cells evolved to the diversity of living things we have on Earth today!! This likely involved many, many different mutations over time. Survival was likely determined through natural selection (“survival of the fittest”).