Theories of the Origin of Life Chapter 19.3 SC.912.L.15.8 Describe the scientific explanations of the origin of life on Earth

Scientific Theory Vs. Scientific Law Scientific theories and laws are very similar but different things. Scientific Theory Explains a natural phenomenon Based on observations and data 99% proven, can change over time with new evidence Scientific Law States a natural phenomenon exist Based on quantitative data 100% proven Can never change

Theories on the Origin of Life The origin of life is a big mystery that scientist have been trying to solve for years. There are many theories of where life began on Earth. Aristotle 350 BCE Spontaneous generation theory – life comes out of nowhere Pasteur 1864 Biogenesis- life comes from other life Arrhenius Panspermia 1903 Panspermia theory – life came from out of space in asteroids Oparin Primordial Soup Theory 1924 Early life came from primitive molecules based on chemicals Modern Theories 1950 – present Chemical Evolution RNA world

Early Earth’s Atmosphere Earth’s early atmosphere contained little or no oxygen. It was principally composed of carbon dioxide, water vapor and nitrogen, with lesser amounts of carbon monoxide, hydrogen sulfide and hydrogen cyanide.

Early Atmosphere: Production of Oxygen Microscopic fossils evidence shows that prokaryotes resembling bacteria have been found in Archean rocks dating 3.5 billion years old. These evolved in the absence of oxygen Fossil evidence also shows that photosynthetic bacteria began producing oxygen about 2.2 billion years ago. The increase of oxygen reduced the prokaryotes bacteria and organisms that evolved new metabolic ways to use oxygen for respiration increased.

Organic Molecules: Primordial Soup Theory The primordial soup theory was hypothesis by various scientist that build on each others work. Alexander Oparin in 1922s had believed that organic molecules had developed from the gases of Earth’s early atmosphere. However he wasn’t able to perform experiments. Miller and Urey in the 1950’s conducted a series of experiments on the same hypothesis.

Organic Molecules: Primordial Soup Theory – Miller and Urey In 1953 chemist Stanley Miller and Harold Urey tried to answer the question: “Could organic molecules assemble under conditions on early Earth’s atmosphere?” Experiment: Used a flask of water to simulate ocean, boiled it and added methane, ammonia and hydrogen to simulate early Earth’s atmosphere. The passed the gases through electricity to simulate lightning. Then passed them through condensed chamber, to create rain drops (water cycle) Circulated the experiment in the apparatus for a week. Results Brown water that contained 21 amino acids, building blocks of proteins.

Organic Molecules: Primordial Soup Theory Miller and Urey’s experiment suggested how mixtures of the organic compounds necessary for life could have arisen from simpler compounds on a primitive Earth. However: Miller and Urey’s ideas of early Earth’s atmosphere were incorrect. New experiments based on current ideas of the early atmosphere have also produced organic compounds, in 1995 Miller’s more accurate mixture produced cytosine and uracil, 2 bases found in RNA.

Organic Molecules: Endosymbiosis -Margulis Endosymbiotic theory by scientist Lynn Margulis hypothesis that about 2 billion years ago some ancient prokaryotes began evolving internal cell membranes. Remember that there are two types of cell known as of today: Prokaryotic Cells Bacteria No nucleus No other membrane-bound organelle Eukaryotic Cells Single celled or multi cell organism Animals, plants, fungi Organelles nucleus

Organic Molecules: Endosymbiotic Theory - Margulis These prokaryotes were the ancestors of eukaryotic organisms today. According to Endosymbiotic theory prokaryotic cells entered those ancestral eukaryotic cells. They did not infect their host, as parasites, host cell didn’t digest them, instead the prokaryotic cell began living inside the eukaryotic cell. Endosymbiotic theory proposes that symbiotic relationships evolved over time, between primitive eukaryotic cells and the prokaryotic cells within them.

Organic Molecules: Endosymbiotic Theory - Margulis This was proposed based on the data observed by scientist a century ago. They observed that mitochondria and chloroplast resembled the cell membrane of free living prokaryotic cells. This led to the hypothesis and theory. Margulis found data that could support this theory in 1960.

Chemical Evolution The idea that earliest organisms on Earth evolved from simple compounds to more complex through a series of events using chemicals and some form of spark. Various theories are included under chemical evolution: Miller and Urey’s theory – early atmosphere with a spark Deep Sea vent Theory – deep ocean chemosynthesis Spark theory – a spark with chemicals

Chemical Evolution Theory Early Earth’s atmosphere was radically different – nitrogen, carbon dioxide, water vapor Reducing, not oxidizing atmosphere like today. A series of chemical reactions spark first life Energy such as solar radiation drove these reactions Organic molecules evolved from simple to complex

Scientific Theory The theories on the Origin of Life are all scientifically accepted theories that are based on observational data and evidence that supports those theories to an extend, however they do not prove 100% the origin of life and therefore are only accepted scientifically theories. They explain a possible origin but do not prove it completely. A scientific law would not explain the origin of life but state it as a fact based on 100% prove. The scientific body of knowledge is based on work, research, data and ideas from past scientist that continues to build forward.