The History of Life

What is Biogenesis? Biogenesis states that all living things come from other living things spontaneous generation Before the 1600’s A process in which something arises from nothing

What Caused the Downfall of Spontaneous Generation? Redi’s Experiment It was widely accepted that flies spontaneously generated from rotting meat. Francesco Redi studied the developmental forms of flies He saw that maggots were often found places after adult flies had previously landed He noted that maggots ultimately led to the development of adult flies

What Caused the Downfall of Spontaneous Generation? In 1668 Redi conducted an experiment to prove that maggots could only come from adult flies, and not rotting meat Maggots Appear Uncovered Jars Covered Jars No Maggots Appear His results showed that files only came from eggs, in opposition to the idea of spontaneous generation

What Caused the Downfall of Spontaneous Generation? Spallanzani’s Experiment 1700s, Lazzaro Spallanzani tested spontaneous generation of microorganisms He boiled one flask of meat broth and immediately sealed it after boiling He boiled another flask of meat broth and let it sit out unsealed Sealed flasks remained clear Unsealed flasks became cloudy from microorganisms

What Caused the Downfall of Spontaneous Generation? Broth is boiled. Flask is sealed. open. Broth becomes cloudy with microorganisms. Broth is free of microorganisms.

What Caused the Downfall of Spontaneous Generation? Pasteur’s Experiment Louis Pasteur set out to confirm that spontaneous generation is not possible in the mid-1800s Pasture conducted a similar experiment to Spallanzani instead of sealing the flask shut, he made a curved-neck flask that allowed air in, but kept microorganisms out After boiling, the broth remained clear for a year He broke the neck off of his flask, and the broth became contaminated with microorganisms The led to the downfall of spontaneous generation, and the acceptance of biogenesis

What Caused the Downfall of Spontaneous Generation? Broth is boiled. Broth is free of microorganisms for a year. Curved neck is removed. Broth is teeming with microorganisms.

Earth’s History

What was Earth’s Early History? The Formation of the Earth The estimated age of the Earth is over 4 billion years old Radiometric dating allowed scientists to determine the age of the Earth Isotopes atoms of an element with a different number of neutrons Mass number of an isotope the total number of protons and neutrons for an atom

What was Earth’s Early History? Some isotopes have unstable nuclei that undergo radioactive decay Half-Life The length of time that it takes for one-half of any size sample of an isotope to decay The age of a material can be determined by measuring the amount of a particular radioactive isotope it contains Carbon-14 is a radioactive isotope of carbon. Scientists can compare the amount of carbon-14 found in a sample to the amount of carbon-12 (which is not radioactive) to determine the sample’s age To determine the age of the Earth, scientists use the decay of uranium and thorium isotopes found in rock crystals

Radioactive Decay

What Were the First Organic Compounds? All of the elements found in organic compounds are believed to have existed on Earth and in the rest of the solar system when Earth was formed How did they form the organic compounds found in life?

What Were the First Organic Compounds? Simple Organic Molecule Formation “The Primordial Soup Hypothesis” Alexander Oparin thought that Earth’s early atmosphere was VERY different than it is today He believed it was made of ammonia, hydrogen gas, water vapor and compounds made of carbon and hydrogen He believed these gases could have produced the first organic compounds in the early oceans

What Were the First Organic Compounds? UV light from the sun, and energy from lightening could have been the energy sources needed to fuel these reactions As the Earth cooled, and water vapor condensed to form lakes and seas, the organic compounds could be found in the water Over time, the organic compounds could have undergone chemical reactions (fueled by lightening and UV radiation) to form biological macromolecules

What Were the First Organic Compounds? Stanley Miller and Harold Urey 1953 Used Oparin’s hypotheses to conduct experiments that resulted in the production of organic compounds Recently, is has been suggested that Earth’s atmosphere was made of CO2, water vapor and N2 gas These conditions would not allow for the production of organic compounds Some hypothesize that areas found by undersea hot springs may have produced organic compounds 1/25/10

Miller and Urey Mixture of gases simulating atmospheres of early Earth Spark simulating lightning storms Condensation chamber Cold water cools chamber, causing droplets to form Water vapor Liquid containing amino acids and other organic compounds

How Were the First Cells Formed? From Molecules to Cell-like Structures Cell-like structures that may have led to the first cells Microspheres made of many protein molecules in a membrane Coacervates collections of droplets that are made of molecules like amino acids and sugars Both of these form spontaneously in certain kinds of solutions. Microspheres can bud to form smaller microspheres, while cocervates can grow These cell-like structures are NOT alive and also lack hereditary characteristics P1 1/24

The First Life-Forms

What Were the First Life Forms? The origin of Heredity The first molecule that held hereditary information may have been RNA rather than DNA. serve as a template for protein assembly some RNA molecules can act as self-replicating enzymes called ribozymes.

What Were the First Life Forms? The First Prokaryotes When the first organisms arose, there was no oxygen, which means they were anaerobic It is believed that the first prokaryotic cells were heterotrophs feeding on organic molecules This resulted in the need for autotrophic organisms

What Were the First Life Forms? Chemosynthesis no oxygen the first autotrophic cells did not use photosynthesis These cells used chemosynthesis to produced food CO2 is used as the carbon source The energy comes from inorganic substances like sulfur Archea are prokaryotic cells living today in harsh environments that used chemosynthesis

What Were the First Life Forms? Photosynthesis & Aerobic Respiration Photosynthetic organisms such as cyanobacteria produced O2 as a byproduct of photosynthesis Since O2 could damage enzymes essential for life, organisms developed a way to bond O2 to other compounds to prevent damage Scientists believe this was one of the first steps in aerobic respiration It took a billion years for the O2 levels to reach where they are today As the O2 reached the upper levels of the atmosphere, it reacted with the UV radiation from the sun forming the ozone

What is Endosymbiotic Theory? The First Eukaryotes Eukaryotes developed from endosymbiosis a mutual relationship between two prokaryotic cells A small, aerobic prokaryote entered a larger prokaryote and was able to live and reproduce modern day mitochondria There was a second, successful invasion in which a small, photosynthetic cell was able to live and reproduce in a larger prokaryote chloroplasts

What is Endosymbiotic Theory? Chloroplast Plants and plantlike protists Aerobic bacteria Ancient Prokaryotes Nuclear envelope evolving Photosynthetic bacteria Primitive Photosynthetic Eukaryote Animals, fungi, and non-plantlike protists Ancient Anaerobic Prokaryote Primitive Aerobic Eukaryote

What is Endosymbiotic Theory? Evidence for Endosymbiont Theory Mitochondria and chloroplasts have their own DNA Their DNA is circular, similar to prokaryotic DNA Mitochondria and chloroplasts have ribosomes similar to prokaryotic cells Mitochondria and chloroplasts reproduce by binary fission, independent from the rest of the cell