Topic 15 Theory of Evolution Day 1

Origins of Life

Benchmarks SC.912.L Describe the scientific explanations of the origin of life on Earth. AA SC.912.N Recognize that the strength or usefulness of a scientific claim is evaluated through scientific argumentation, which depends on critical and logical thinking, and the active consideration of alternative scientific explanations to explain the data presented. SC.912.N Identify sources of information and assess their reliability according to the strict standards of scientific investigation. SC.912.N Identify what is science, what clearly is not science, and what superficially resembles science (but fails to meet the criteria for science).

Objectives SWBAT... Explain several scientific explanations for the origin of life. Explain how the scientific claims are strengthened through scientific argumentation. Identify a theorist’s sources of information and assess their reliability according to the strict standards of scientific investigation. Explain why theories on the origins of life are considered “science” and contrast them with explanations that are not considered science and with what superficially resembles science (but fails to meet the criteria for science).

Essential Questions If the work of many scientists has shown that spontaneous generation does not occur, and the idea of biogenesis is true, how do we explain the origin or the first living things?

How did life begin on Earth? Remember... According to the cell theory, life only comes from life, new cells only come from pre-existing cells. This is called biogenesis. If this is true, then how did life on Earth first begin?

How did life begin on Earth? There have been a few hypotheses for how life first appeared on early Earth. However, even today’s strongest hypotheses are based on a relatively small amount of evidence. Therefore, the gaps and uncertainties make it likely that scientific ideas about the origins of life will continue to change over time.

Can generate amino acids and sugars from an atmosphere loaded with water, methane, ammonia and hydrogen Demonstrated in the famous Miller-Urey experiment reported in 1953 New evidence suggest that it may have occurred in volcanic clouds These vents release important hydrogen-rich molecules Mineral catalysts could have made critical reactions occurs faster Discover of Archea bacteria may be evidence of this HOW did life Begin? Hydrothermal Vents Electric Spark Video

Clay may have provided the foundation for first organic compounds. Mineral crystals in clay could have arranged organic compounds into organized patterns. Life could have come from outer space in a comet or meteorite. HOW did life Begin? Panspermia Community Clay 3 billion years ago ice might have covered the oceans. Protected from UV light, organic compounds may have formed and reacted with one another. Ice Earth

Early Earth The Earth was formed about 4.5 billion years ago. The oldest fossils of microorganisms are about 3.5 billion years old. But where did they come from???

Theories - Spontaneous Generation Until the early 19th century, people generally believed in the “Spontaneous Generation” of life from non-living matter. Francisco Redi (1668) – Rotten Meat Experiment Louis Pasteur (1864) – Curved Flask Experiment

Theories - Chemical Evolution Conditions on the early Earth were very different from the Earth we know today. The early atmosphere contained no free oxygen and probably contained hydrogen cyanide, carbon dioxide, carbon monoxide, nitrogen, hydrogen sulfide and water. Energy for chemical reactions between these gases could come from electric discharge in storms or solar energy (no ozone layer). Could organic molecules have evolved under these conditions?

Theories - Chemical Evolution Alexander Oparin (1920’s), hypothesized that organic molecules could form. In the 1950‘s Harold Urey and Stanley Miller tried to answer that question by simulating the conditions on the early Earth in a laboratory setting. Mixture of gases simulating primitive atmosphere of early Earth Spark simulating lightning storms Water vapor Liquid containing Amino Acids (15) and other organic compounds Cold water cools chamber, it condenses the gas causing droplets to form (Rain). Stopcock for taking samples Methane CH 4 Ammonia NH 3 Hydrogen H 2 Water Vapor H 2 O

Theories - Chemical Evolution Miller and Urey's experiments suggested how mixtures of the organic compounds necessary for life could have arisen from simpler compounds present on a primitive Earth. This formation of organic molecules (such as amino acids, sugars, fatty acids, and nucleotide bases ) from inorganic molecules is also known as abiogenesis.

MacromoleculeWhere it is foundWhat it does ProteinMeat (Muscle), Fish, CheeseEnzymes, structural, transportation, hormones, to move, among many other functions in living organism. CarbohydrateSugar, Breads, Fruits, Pasta, Rice (thank you plants) Short term energy LipidCell membranes Fats Long term energy storage; an important component of the cell membrane. Nucleic AcidRNA and DNACarries genetic information Why were scientists trying to synthesis basic organic compounds in a simulated primitive Earth’s atmosphere? Because basic amino acids are the building blocks of all Life on Earth. It gives evidence that living things could have started on Earth from these simple molecules. Why were scientists trying to synthesis basic organic compounds in a simulated primitive Earth’s atmosphere? Because basic amino acids are the building blocks of all Life on Earth. It gives evidence that living things could have started on Earth from these simple molecules.

The First Cells Geological evidence suggests that cells similar to modern bacteria were common 3.8 billion years ago. However the stew of organic molecules suggested by Miller and Urey is a long way from a living cell. So how could the first cells on Earth have originated? Sydney Fox (1950’s) and others have done extensive research on the structures that may have given rise to the first cells.

The First Cells Organic molecules have a tendency to aggregate. Remember… Phospholipids form lipid bilayers when they are surrounded by water. As a result, membrane-like vesicles called coacervates, form easily under certain conditions. Video Clip

Coacervates Coacervates are made mostly of aggregated lipids. They grow by adding new polymers. They form a semi-permeable membrane. When they get too big they divide. Hypotheses suggest that structures similar to microspheres might have acquired more characteristics of living cells.

The Origin of Heredity Remember… One of the characteristics of life, is that all living things contain hereditary information (DNA) which is passed from cell to cell during cell division. Scientists speculate that RNA may actually have been the first hereditary molecule. There are several hypotheses for how RNA could have evolved into modern cellular life.

The First Eukaryotic Cells The Endosymbiotic Theory, proposed by Lynn Margulis in 1967, proposes that eukaryotic cells arose from living communities formed by prokaryotic organisms. According to the theory, eukaryotic cells formed from a symbiosis among several different prokaryotes. Mitochondrion Aerobic bacteria Nuclear envelope evolving Plants and plantlike protists Primitive Photosynthetic Eukaryote Primitive Aerobic Eukaryote Ancient Anaerobic Prokaryote Animals, fungi, and non-plantlike protists Photosynthetic bacteria

Notice It took many scientist to build on the evidence from each other (each had only a few pieces of evidence) to come up with a modern hypothesis of the origin of life. Do you think this hypothesis will change further? Who has the picture on the puzzle box …How much of the picture do we actually see?… hmmmmm Notice It took many scientist to build on the evidence from each other (each had only a few pieces of evidence) to come up with a modern hypothesis of the origin of life. Do you think this hypothesis will change further? Who has the picture on the puzzle box …How much of the picture do we actually see?… hmmmmm

Which of the Following best describes current scientific thinking about the origins of life on Earth? A. It has been proven that life came to Earth on comets B. Scientific explanations have changed based on new information C. Fossil evidence of the earliest form of life is common and well accepted. D. The creation of organic molecules in ancient “soup” is the only possible explanation for the origin of life on Earth.

Which is NOT considered a possible location on Primitive Earth where conditions would have allowed the synthesis of complex organic compounds? F. Near volcanoes G. Dry, Hot deserts H. Deep ocean vents I. Shallow seashores

When they analyzed the results of the experiment, they found that simple organic molecules were formed. What kind of molecules did they find? F.Lipids G. Proteins H.Amino Acids I. Nucleic Acids