Origin of Life PDF

Introduction to Biology Origin of Life Mansura Khan Lecturer Contents Dept of Cellular & Molecular Biolog...

Introduction to Biology Origin of Life Mansura Khan Lecturer Contents Dept of Cellular & Molecular Biology Faculty of Biotechnology & Genetic 1. Early history of the universe Engineering, CVASU 2. Origin of the Earth 3. formation of the continents and the oceans 4. Definition and key characteristics of life 5. Theories on the origin of life 6. Pre-biological formation of precursor and macromolecules 7. Theories on the origin of cells; fossils of ancient microorganisms 8. The three types of cells 9. Species concept 10. Classification of living things and domains of life 11. Historical geology and the scale of biological time Early history of the universe The early history of the universe is a fascinating and complex topic that combines physics, astronomy, and cosmology. It describes the series of events that unfolded after the universe’s creation, leading to the formation of matter, galaxies, and life as we know it. This note outlines key stages in the universe's evolution based on the Big Bang Theory, which is the leading scientific explanation. Early history of the universe is characterized by the following events: The Big Bang Cosmic inflation Nucleosynthesis The universe cools The universe becomes transparent The first stars and galaxies form The cosmic dark ages 1. The Big Bang (Time: 0 seconds)  The universe began as a singularity, an infinitely hot and dense point.  At time zero, the Big Bang occurred, marking the rapid expansion of space itself.  This event created the fundamental forces of nature and the fabric of space-time. 2. Planck Epoch (Time: 0 to 10^-43 seconds)  This is the earliest period of the universe, where physics as we understand it breaks down.   All four fundamental forces (gravity, electromagnetism, strong nuclear, and weak nuclear) were unified.  The temperature was extremely high, and no matter existed, only pure energy. 3. Grand Unification Epoch (Time: 10^-43 to 10^-36 seconds)  Gravity separated from the other three forces.  The universe continued to expand and cool.  The strong nuclear force began to differentiate from the electroweak force. 4. Inflationary Epoch (Time: 10^-36 to 10^-32 seconds)  A rapid expansion called cosmic inflation occurred, exponentially increasing the size of the universe.  Tiny quantum fluctuations during inflation were stretched, seeding the formation of large-scale structures like galaxies. 5. Electroweak Epoch (Time: 10^-36 to 10^-12 seconds)  The universe cooled enough for the strong nuclear force to fully separate.  The electromagnetic and weak nuclear forces were still unified as the electroweak force. 6. Quark Epoch (Time: 10^-12 to 10^-6 seconds)  As the universe cooled further, quarks (the building blocks of protons and neutrons) began to form.  The universe was a hot, dense soup of quarks, leptons, and gluons. 7. Hadron Epoch (Time: 10^-6 seconds to 1 second)  Quarks combined to form hadrons (protons and neutrons).  Anti-matter and matter collisions led to annihilation, leaving a slight excess of matter. 8. Lepton Epoch (Time: 1 second to 10 seconds)  Leptons, such as electrons and neutrinos, dominated the universe.  Neutrinos decoupled and began to travel freely, forming the cosmic neutrino background. 9. Photon Epoch (Time: 10 seconds to 380,000 years)  Photons dominated the energy content of the universe.  The universe was still too hot for atoms to form, so photons interacted with free electrons and protons.  This period ended with the ―recombination‖ era. 10. Recombination Era and Cosmic Microwave Background (Time: ~380,000 years)   The universe cooled enough for electrons to combine with protons, forming neutral hydrogen atoms.  Photons decoupled from matter and began traveling freely, creating the cosmic microwave background (CMB), a snapshot of the early universe. 11. Dark Ages (Time: 380,000 years to 150 million years)  No stars or galaxies existed; the universe was filled with neutral hydrogen.  Gravity slowly pulled matter together, leading to the formation of the first stars and galaxies. 12. Formation of the First Stars and Galaxies (Time: ~150 million years)  The first stars ignited through nuclear fusion, producing light and heat.  These stars formed within protogalaxies, which evolved into larger galaxies over time.  Heavier elements were synthesized in these stars through stellar nucleosynthesis. 13. Reionization Era (Time: ~550 million years)  Radiation from the first stars and galaxies ionized the neutral hydrogen.  The universe became transparent to ultraviolet light, marking the end of the Dark Ages. 14. Structure Formation (Time: ~1 billion years onwards)  Galaxies, galaxy clusters, and large-scale structures continued to form under the influence of gravity.  The cosmic web of filaments and voids became apparent. Big Bang Theory According to this theory, all matter that formed the universe existed in one point (tiny ball) called singularity having an unimaginable small volume, infinite temperature and infinite density. The great event of the big bang happened some 13.7 billion years ago. The tiny ball exploded which led to a huge expansion and this expansion continues even today. There was rapid expansion within fractions of a second after the bang. Thereafter, the expansion slowed down. With the expansion some of the energy was converted into matter. Within the first three minutes from the big bang event, the first atom began to form. Within 300,000 years from the big bang, temperature dropped down to 4500 K and gave rise to atomic matter. The majority of atoms formed were hydrogen, along with helium and traces of lithium. Huge clouds of these elements fused through gravity to form stars and galaxies. Once there were two theories for explaining the origin of the universe – the Big Bang theory and the Hoyle’s concept of steady state. The steady state theory considered the universe to be roughly the same at any point of time.  However, with greater evidence becoming available about the expanding universe, the Big Bang theory was confirmed which proposes that the universe originated from a single violent explosion of a very minute amount (tiny ball) of matter of high density and temperature. Origin of Earth The origin of the Earth is a pivotal topic in understanding planetary science and the evolution of the solar system. This note explores the process by which the Earth formed, from the birth of the solar system to the early stages of Earth's development, based on the widely accepted nebular hypothesis. The earth was a barren, rocky and hot object with a thin atmosphere of hydrogen and helium. Lithosphere – With the increasing density, the temperature inside the earth increased and the materials started getting separated depending on their densities. The heavier elements like iron moved towards the centre and lighter ones moved towards the surface. With the passage of time the earth cooled, solidified and condensed into a smaller size and formed the crust (the outer layer of the earth). The different layers of the earth starting from the surface are crust, mantle, outer core and inner core. From crust to the core, density increases. Atmosphere – The solar wind was most intense nearer the sun; so it blew off lots of gas and dust from the terrestrial planets – Mercury, Venus, Earth and Mars. During the process of cooling of earth, gases and water vapour escaped from the interior of the earth thereby starting the evolution of the present atmosphere. The early atmosphere mainly had water vapour, carbon dioxide, nitrogen, methane, ammonia and small amounts of free oxygen. The process of release of gases from the interior of the earth is called ―degassing‖. Hydrosphere – The frequent volcanic eruptions provided the atmosphere with water vapour and gases. With the cooling of the earth, water vapours condensed and brought rain. The carbon dioxide in the atmosphere got dissolved in rainwater which further lowered the temperature leading to more condensation and more rain. The rain water got collected into depressions to give rise to oceans. Life was limited to oceans only for a long time. Oceans got saturated with oxygen through the process of photosynthesis and then some 2,000 million years ago oxygen began to flood the atmosphere 1. Formation of the Solar System (~4.6 billion years ago)  The solar system formed from a giant molecular cloud of gas and dust.  A nearby supernova or other cosmic event triggered the collapse of this cloud under gravity.  The collapsing cloud formed a spinning protoplanetary disk, with the Sun forming at the center. 2. Accretion of Planetary Materials  Within the disk, small particles of dust and ice collided and stuck together due to electrostatic forces, forming planetesimals.  Planetesimals grew through accretion, colliding to form larger bodies known as protoplanets.  In the region of the Earth, rocky materials dominated due to high temperatures closer to the Sun. 3. Differentiation and Early Structure of the Earth  As the Earth grew in size, gravitational forces increased, causing it to become spherical.  Heat from accretion, radioactive decay, and impacts melted the planet partially.  Heavy elements like iron and nickel sank to the center, forming the core, while lighter silicates rose to form the mantle and crust. 4. Formation of the Moon (~4.5 billion years ago)  The Moon likely formed through the Giant Impact Hypothesis: o A Mars-sized protoplanet, called Theia, collided with the early Earth. o The impact ejected a significant amount of material into orbit around Earth. o This material coalesced to form the Moon.  Evidence for this includes the Moon’s composition, which is similar to Earth’s mantle. 5. Cooling and Crust Formation  As Earth cooled, the surface solidified to form a primitive crust.  Volcanic activity released gases, forming the early atmosphere.  Water vapor condensed to form oceans as the planet cooled further. 6. Development of the Atmosphere and Oceans  The early atmosphere was primarily composed of hydrogen, helium, and volcanic gases like carbon dioxide, methane, ammonia, and water vapor.  Cometary impacts and volcanic outgassing contributed additional water to Earth’s surface.  The presence of liquid water enabled the development of stable oceans, crucial for the origin of life. 7. The Hadean Eon (4.6 to 4 billion years ago)  This was a chaotic period marked by frequent meteorite impacts and intense volcanic activity.  The Earth’s surface was hostile, with high temperatures and a lack of free oxygen.   Despite the harsh conditions, the building blocks of life, such as organic molecules, may have started forming during this time. 8. Evidence Supporting Earth’s Formation  Radiometric dating of meteorites suggests the solar system’s age is about 4.6 billion years.  Moon rocks and Earth’s oldest minerals, such as zircon crystals, provide clues about early Earth conditions.  Computer simulations of planetary formation align with the nebular hypothesis. Formation of the continent and the ocean  The Earth's continents and oceans formed through complex geological and tectonic processes over billions of years.  Understanding their formation involves studying the Earth's structure, plate tectonics, and geological history. Formation of Continents 1. Primordial Earth and Crust Formation: o Around 4.6 billion years ago, the Earth formed from the solar nebula. o The early Earth was hot, and its surface was molten; as it cooled, a solid crust formed. 2. Formation of the First Continents (Archean Eon, ~4.0–2.5 billion years ago): o The first landmasses, called cratons, formed from volcanic activity and the accumulation of lighter, silica-rich rocks. o Plate tectonics began operating, driving the collision and amalgamation of smaller landmasses into larger continental plates. 3. Growth of Continents: o Over time, continental crust grew through magmatic addition, sediment deposition, and tectonic activity. o Supercontinents such as Rodinia, Pannotia, and later Pangaea formed and broke apart due to tectonic forces. Formation of Oceans 1. Primitive Oceans (~4.4 billion years ago): o Water on Earth likely originated from volcanic outgassing and comet impacts, leading to the accumulation of water vapor. o As the Earth cooled, water vapor condensed to form the first oceans. 2. Influence of Plate Tectonics: o Oceans developed as tectonic plates shifted, creating basins where water accumulated.  o Mid-ocean ridges, trenches, and other features shaped by tectonic activity contributed to ocean formation. 3. Continental Breakup and Ocean Formation: o The breakup of supercontinents, such as Pangaea (~200 million years ago), created modern ocean basins like the Atlantic Ocean. o Subduction zones and seafloor spreading continue to reshape oceanic boundaries. Plate Tectonics Fundamental concept in geology that explains the movement of Earth’s lithosphere, the rigid outer shell, in large, distinct plates. The interactions and movements of these plates play a pivotal role in shaping the geological evolution of our planet. Here are key aspects of how plate tectonics influence geological evolution. Divergent Boundaries: At divergent boundaries, tectonic plates move away from each other. This movement leads to the upwelling of molten rock from the mantle, creating mid-ocean ridges. As new crust forms and spreads, it gradually pushes older crust aside. Divergent boundaries are responsible for the creation of ocean basins and contribute to the overall growth of Earth’s crust. Convergent Boundaries: Convergent boundaries are characterized by the collision of tectonic plates. When an oceanic plate collides with a continental plate, the denser oceanic plate is subducted beneath the continental plate, creating deep ocean trenches and volcanic mountain ranges on the continental plate. When two continental plates collide, they can form massive mountain ranges, such as the Himalayas. The intense geological activity at convergent boundaries results in the formation of mountain chains, earthquakes, and volcanic arcs. Transform Boundaries: At transform boundaries, tectonic plates slide past one another horizontally. The friction and stress between plates build up over time until they suddenly release, causing earthquakes. The San Andreas Fault in California is a well-known example of a transform boundary. The movement of plates along transform boundaries can lead to the creation of fault lines, and their interactions play a crucial role in shaping the Earth’s crust. Hotspots: Hotspots are areas of intense volcanic activity that are not associated with plate boundaries. Instead, they occur as a result of plumes of hot mantle material rising through the Earth’s lithosphere. As the overlying tectonic plate moves, it creates a chain of volcanic islands or seamounts. The Hawaiian Islands, for example, were formed by the Pacific Plate moving over a hotspot. Subduction Zones: Subduction zones, typically found at convergent boundaries, are regions where one tectonic plate is forced beneath another. The descending plate melts and forms magma in the mantle, which can lead to volcanic arcs and the release of heat and pressure that drive seismic activity. Subduction zones are key features in the formation of island arcs, deep-sea trenches, and volcanic mountain ranges. The formation of continents and oceans significantly affected Earth’s climate, geology, and the evolution of life.  Continents provided a variety of environments for different ecosystems to thrive, while oceans played a role in regulating Earth’s climate and supporting marine life. This dynamic interplay between the Earth’s geology, its changing atmosphere, and the emergence of life continues to be a fascinating subject of study in Earth sciences Definition and Key Characteristics of Life Definition of Life Life refers to the condition that distinguishes living organisms from non-living matter. Living organisms are characterized by their ability to grow, reproduce, maintain homeostasis, respond to stimuli, and carry out metabolic processes. Key Characteristics of Life Scientists have identified several criteria that are used to define living organisms. These characteristics include: 1. Cellular Organization o All living organisms are composed of one or more cells. o Cells are the basic structural and functional units of life. o Organisms can be unicellular (e.g., bacteria) or multicellular (e.g., humans). 2. Metabolism o Life involves the continuous intake of energy and matter to sustain processes such as growth and reproduction. o Metabolism includes:  Anabolism: Building complex molecules from simpler ones (e.g., protein synthesis).  Catabolism: Breaking down molecules to release energy (e.g., cellular respiration). 3. Growth and Development o Living organisms grow by increasing in size or cell number. o Development refers to the changes an organism undergoes during its life cycle (e.g., metamorphosis in butterflies). 4. Reproduction o All living things have the ability to reproduce and pass on genetic information to offspring. o Can be asexual (e.g., binary fission in bacteria) or sexual (e.g., reproduction in humans). 5. Homeostasis o The ability of an organism to maintain a stable internal environment despite external changes. o Examples include temperature regulation and pH balance.  6. Response to Stimuli o Organisms can detect and respond to changes in their environment. o Responses may involve movement, changes in behavior, or physiological adaptations (e.g., plants growing toward light). 7. Evolutionary Adaptation o Over generations, living organisms evolve through changes in genetic material. o Evolution enables organisms to adapt to their environment, improving survival and reproduction. 8. Heredity o All living things possess a genetic system based on DNA, which allows traits to be passed from one generation to the next. Non-Living vs. Living: Borderline Cases  Viruses: o Contain genetic material and can evolve. o However, they lack cellular structure and cannot metabolize or reproduce independently.  Prions: o Proteinaceous infectious agents that replicate abnormally but lack other features of life.  Key Characteristics of Life Biology is the study of living things. The definition of life, however, has been routinely debated for centuries. A modern list of the characteristics of living things includes several components. The key structural characteristic of a living thing is that it is composed of at least one cell. An organism may consist of a single cell, a few thousand cells, or—in the case of large mammals— trillions of cells. Each cell is separate, enclosed in its own membrane. In multicellular organisms, connections between cells allow them to work together within the organism. Living things use energy to carry out life processes. They take in and metabolize nutrients, and they excrete waste products from chemical reactions. Plants and some bacteria are able to synthesize energy-rich molecules from nonliving sources. Animals, fungi, and most bacteria must consume food produced by other living organisms. While the sources of energy may differ among organisms, many of the chemical reactions carried out by their cells are the same. A living organism, whether single-celled or multicellular, uses energy to keep its internal conditions (temperature, pH, concentrations of various elements and molecules) stable regardless of external conditions, known as homeostasis. One example of homeostasis in the human body is the maintenance of a body temperature within the range of 97°F—99°F, with a typical set point of 98.6°F. While maintaining their internal environment, living things detect and respond to their external environment. Some animals have sophisticated nervous systems to carry out information processing, but even the simplest bacterial cells can respond using chemical-sensing systems. Maintaining a proper body temperature is one example of homeostasis (maintaining internal environment). The normal value, or set point, of the temperature of the human body is 98.6°F. Temperatures from 97°F to 99°F are a normal range of variation. If the body temperature rises above that range (fever) or drops below it (hypothermia), cells in the body respond in order to restore a normal temperature. Living things grow and undergo change throughout their lives. Asexually reproducing organisms experience this as they develop from immature clonal stages to their adult forms and continue to develop afterward. Sexually reproducing organisms experience this as they develop from fertilized eggs to mature adults. Even a single-celled bacterium increases in size as a precursor to dividing. The timing and sequence of an organism's developmental stages is controlled by its genes and environmental factors. A gene is a unit of heritable material that codes for a particular trait. Genes are sections of a nucleic acid molecule called deoxyribonucleic acid. Deoxyribonucleic acid (DNA) is an organic molecule containing coded instructions for the life processes of an organism. This DNA consists of nucleotides bonded together in the form of a double-helix molecule that allows for genetic inheritance in all living organisms. All living things reproduce, forming the next generation and passing on their traits to their offspring. Reproduction may be sexual, requiring the contributions of two parent organisms and resulting in genetic variations. Conversely, reproduction may be asexual, or carried out by one parent organism and resulting in genetically identical offspring. Evolution ("change over time") occurs within a species as individuals with the most advantageous traits for a particular environment survive and reproduce to a greater extent than other individuals in that environment. Such selective survival and reproduction produces changes in gene frequency from one generation to the next. Offspring with versions of genes most suited for survival in a given environment survive and reproduce more successfully in that environment. However, significant changes in the environment will favor the survival and reproduction of individuals best suited for those later changes. Thus, having a variety of versions of genes in a population increases that population's chances of surviving and reproducing in a wide range of environments and environmental changes Origin of Life Introduction The origin of life is a fundamental question in biology and Earth sciences. It explores how life emerged from non-living matter, a process known as abiogenesis. While the exact mechanisms are still uncertain, several hypotheses and scientific theories attempt to explain this phenomenon. Key Concepts in the Origin of Life 1. Abiogenesis: o Refers to the natural process by which life arose from non-living matter. o Distinguished from biogenesis, which states that life arises from pre-existing life. Early experiments Franceso Redi  Franceso Redi was an Italian naturalist who challenged the ancient belief of spontaneous generation of maggots on decaying meat in 1668.  He designed an experiment where he put pieces of meat in six different containers. He covered two of them with gauze, two tightly sealed with corks and left the remaining two open in the air.  His hypothesis came true as it was observed that there were no maggots in the covered (with gauze and cork) containers but maggots were observed in the open container.  He came to the conclusion that flies were able to lay their eggs on the open piece of meat and that the maggots were their offspring who grew on flesh Pier Antonio Micheli  Pier Antonio Micheli, an Italian botanist, performed another experiment in 1729  where he placed fungal spores on a slice of melon and observed that the same was produced on the melon slice.  He concluded that the new spores definitely did not arise from spontaneous generation. 2. Panspermia Life did not originate on Earth but was seeded here from elsewhere in the universe. Types: 1. Lithopanspermia: Life traveled on meteoroids or asteroids. 2. Radiopanspermia: Microorganisms were carried by radiation pressure through space. 3. Directed Panspermia: Proposed by Francis Crick, suggesting that intelligent extraterrestrial beings might have deliberately seeded life on Earth.Scientific Theories and Hypotheses 3. Deep-Sea Hydrothermal Vent Hypothesis  Definition: Life originated at hydrothermal vents on the ocean floor.  Rationale: o Rich in minerals and energy sources like hydrogen sulfide. o Unique environments could catalyze chemical reactions leading to the formation of organic molecules.   Example: The alkaline hydrothermal vent model, which suggests natural proton gradients drove early biochemical reactions. 4. RNA World Hypothesis  Definition: Early life was based on ribonucleic acid (RNA), which could store genetic information and catalyze chemical reactions.  Key Points:  RNA can self-replicate and act as a catalyst (ribozymes).  DNA and proteins might have evolved later from RNA-based systems. 5. Clay Hypothesis  Proposed by Graham Cairns-Smith.  Concept: Life began on the surfaces of clay minerals, which provided a template for organizing organic molecules.  Clay surfaces might have acted as catalysts for polymerization of organic compounds. 6. Iron-Sulfur World Hypothesis  Proposed by Günter Wächtershäuser.  Suggests that life began on the surface of iron and nickel sulfide minerals, which provided energy for the synthesis of organic molecules 7. Coacervate and Protocell Hypothesis  Oparin proposed that life started with the formation of coacervates—microscopic droplets of organic molecules surrounded by a lipid layer.  These structures could grow, divide, and concentrate molecules, acting as precursors to cells. Pre-Biological Formation of Precursors and Macromolecules Introduction The transition from non-living to living matter involved a series of chemical events, collectively known as chemical evolution. Pre-biological synthesis focuses on the formation of small organic molecules (precursors) and their polymerization into macromolecules, which are essential for life. 1. Formation of Precursors Small organic molecules such as amino acids, nucleotides, and sugars are considered the building blocks of life. These molecules are believed to have formed through chemical reactions in the early Earth’s environment. a. Early Earth Conditions:  Atmosphere: Rich in methane (CH₄), ammonia (NH₃), water vapor (H₂O), and hydrogen (H₂).  Energy Sources: Lightning, ultraviolet radiation, and volcanic activity provided the energy needed for chemical reactions. b. Experimental Evidence:  Miller-Urey Experiment (1953): o Simulated early Earth conditions using a mixture of gases and electrical sparks. o Produced amino acids, demonstrating that simple organic molecules could form naturally. c. Other Sources:  Hydrothermal Vents: Rich in minerals and energy, potentially creating precursors like hydrocarbons and sulfide compounds.  Extraterrestrial Input: Meteorites and comets may have delivered organic molecules such as amino acids to Earth. 2. Polymerization into Macromolecules Once precursors were formed, the next step involved their assembly into larger, more complex macromolecules such as proteins, nucleic acids, and polysaccharides. a. Polymerization Mechanisms:  Condensation Reactions: o Formation of peptide bonds (proteins), glycosidic bonds (carbohydrates), and phosphodiester bonds (nucleic acids). o Removal of water molecules to join monomers.  Catalysis on Mineral Surfaces: o Clay minerals like montmorillonite provided surfaces that catalyzed the polymerization of nucleotides and amino acids.  Thermal Polymerization: o Cycles of heating and cooling in volcanic environments facilitated polymer formation. b. Formation of Protocells:   Protocells are simple, cell-like structures formed by self-assembling lipids and other organic molecules.  Functions: o Enclosure of macromolecules within a lipid membrane. o Concentration of molecules, enabling chemical reactions. 3. Key Macromolecules in Pre-Biological Systems a. Proteins:  Composed of amino acids.  Catalyze chemical reactions (enzymes) and provide structural support. b. Nucleic Acids:  Composed of nucleotides.  Store genetic information (RNA/DNA) and catalyze reactions (ribozymes in RNA). c. Polysaccharides:  Composed of simple sugars.  Serve as energy sources and structural components. d. Lipids:  Amphipathic molecules capable of forming bilayers.  Essential for membrane formation and compartmentalization. Theories on the Origin of Cells and Fossils of Ancient Microorganisms Introduction The origin of cells is a critical step in the evolution of life. Cells, as the fundamental units of life, originated from non-living molecules through chemical evolution and subsequent biological organization. Fossils of ancient microorganisms provide direct evidence of early life on Earth, giving insights into the environmental conditions and evolutionary processes of that time. 1. Theories on the Origin of Cells A. The Prebiotic Chemical Evolution Theory  Proposed by Oparin and Haldane.  Suggests that cells originated from the gradual assembly of organic molecules in Earth's primitive conditions.  Steps:  1. Formation of organic molecules (e.g., amino acids, sugars) from simple gases. 2. Polymerization of these molecules into macromolecules. 3. Formation of protocells (simple cell-like structures). I can't directly extract content from the uploaded images. However, I can create a detailed class note based on the topic "Theories on the Origin of Cells; Fossils of Ancient Microorganisms." Let me draft one for you: Theories on the Origin of Cells and Fossils of Ancient Microorganisms Introduction The origin of cells is a critical step in the evolution of life. Cells, as the fundamental units of life, originated from non-living molecules through chemical evolution and subsequent biological organization. Fossils of ancient microorganisms provide direct evidence of early life on Earth, giving insights into the environmental conditions and evolutionary processes of that time. 1. Theories on the Origin of Cells A. The Prebiotic Chemical Evolution Theory  Proposed by Oparin and Haldane.  Suggests that cells originated from the gradual assembly of organic molecules in Earth's primitive conditions.  Steps: 1. Formation of organic molecules (e.g., amino acids, sugars) from simple gases. 2. Polymerization of these molecules into macromolecules. 3. Formation of protocells (simple cell-like structures). B. The Protocell Hypothesis  Definition: Protocells are self-organized, membrane-bound structures capable of maintaining a distinct internal environment.  Formation: o Lipid molecules self-assemble into bilayer membranes in aqueous environments. o Encapsulation of organic molecules within membranes may have led to the first cellular structures. I can't directly extract content from the uploaded images. However, I can create a detailed class note based on the topic "Theories on the Origin of Cells; Fossils of Ancient Microorganisms." Let me draft one for you: Theories on the Origin of Cells and Fossils of Ancient Microorganisms Introduction The origin of cells is a critical step in the evolution of life. Cells, as the fundamental units of life, originated from non-living molecules through chemical evolution and subsequent biological organization. Fossils of ancient microorganisms provide direct evidence of early life on Earth, giving insights into the environmental conditions and evolutionary processes of that time. 1. Theories on the Origin of Cells A. The Prebiotic Chemical Evolution Theory  Proposed by Oparin and Haldane.  Suggests that cells originated from the gradual assembly of organic molecules in Earth's primitive conditions.  Steps: 1. Formation of organic molecules (e.g., amino acids, sugars) from simple gases. 2. Polymerization of these molecules into macromolecules. 3. Formation of protocells (simple cell-like structures). B. The Protocell Hypothesis  Definition: Protocells are self-organized, membrane-bound structures capable of maintaining a distinct internal environment.  Formation: o Lipid molecules self-assemble into bilayer membranes in aqueous environments. o Encapsulation of organic molecules within membranes may have led to the first cellular structures. C. Endosymbiotic Theory  Proposed by Lynn Margulis.  Describes the origin of eukaryotic cells through symbiotic relationships between prokaryotic organisms.  Key Points: o Mitochondria and chloroplasts originated from free-living bacteria that were engulfed by a host cell.  o Evidence includes the presence of double membranes, circular DNA, and ribosomes in mitochondria and chloroplasts. D. Iron-Sulfur World Hypothesis  Suggests that life originated on iron and nickel sulfide surfaces found in hydrothermal vents.  These environments could catalyze chemical reactions to form organic compounds, leading to cell-like structures. 2. Fossils of Ancient Microorganisms A. Stromatolites  Definition: Layered sedimentary structures formed by the activities of microbial communities, especially cyanobacteria.  Significance: o Provide evidence of life dating back approximately 3.5 billion years. o Found in ancient rock formations in locations like Australia and South Africa. B. Microfossils  Microscopic fossils of individual cells or microbial filaments.  Key Discoveries: o Fossilized cells in 3.4-billion-year-old rocks in Western Australia. o Show morphological evidence of prokaryotic life. C. Chemical Fossils  Organic molecules such as lipids or isotopic signatures preserved in ancient rocks.  Example: o Presence of isotopically light carbon, indicative of biological activity, in rocks older than 3.8 billion years. D. Importance of Fossil Evidence  Confirms that life existed during the Archean Eon (~4.0 to 2.5 billion years ago).  Provides insights into the environmental conditions and metabolic processes of early life. Type of cells There are approximately 200 different types of cells in the human body, but all cells on Earth fit into just two categories; prokaryotes, and eukaryotes Eukaryotic cells are larger and more complex than prokaryotes, and usually contain organelles that are absent from prokaryotic cells. This is because eukaryotes  contain membrane-bound organelles (like the nucleus, endoplasmic reticulum, Golgi apparatus, and mitochondria), but prokaryotes do not Species concept Introduction A species is the fundamental unit of biological classification and biodiversity. The definition of a species has been a subject of debate for centuries, leading to the development of various concepts to understand and classify species. Each concept focuses on different aspects of biology, such as morphology, genetics, ecology, and reproduction. 1. Overview of Species Concepts A. Biological Species Concept  Proposed by: Ernst Mayr (1942).  Definition: A species is a group of individuals that can interbreed in nature and produce viable, fertile offspring, but are reproductively isolated from other such groups.  Key Features: o Focuses on reproductive isolation. o Emphasizes gene flow within a species.  Limitations: o Cannot be applied to asexual organisms, fossils, or species with hybridization. B. Morphological Species Concept  Definition: A species is defined based on observable physical characteristics, such as shape, size, and structure.  Key Features: o Widely used in paleontology and taxonomy. o Useful for identifying species based on morphological differences.  Limitations: o Subjective: Different researchers may classify species differently. o Cannot account for cryptic species (species that are morphologically similar but genetically distinct). C. Ecological Species Concept  Definition: A species is a group of organisms adapted to a particular ecological niche, with unique roles and interactions within the ecosystem.  Key Features: o Focuses on ecological roles and environmental adaptation. o Useful for studying species in ecological and evolutionary contexts.  Limitations: o Overlap in niches among species may cause confusion. D. Phylogenetic Species Concept  Definition: A species is the smallest group of organisms that share a common ancestor and can be distinguished from other groups by unique traits (shared derived characteristics).  Key Features: o Based on evolutionary history and genetic data. o Useful for identifying species using molecular tools like DNA sequencing.  Limitations: o May lead to splitting of species into many smaller groups (over-splitting). E. Genetic Species Concept  Definition: A species is defined based on genetic similarity or distinctness, using molecular data such as DNA or RNA sequences.  Key Features: o Useful for identifying cryptic species. o Helps clarify relationships between closely related species.  Limitations: o Requires advanced technology and resources. o No universal threshold for genetic differences between species. F. Evolutionary Species Concept  Definition: A species is a single lineage of populations that maintains its identity from other lineages and has its own evolutionary trajectory.  Key Features: o Emphasizes evolutionary independence and continuity. o Applies to both sexual and asexual organisms.  Limitations: o Difficult to determine clear lineage boundaries. 2. Importance of the Species Concept  Biodiversity Conservation: Identifying species helps in protecting and conserving biodiversity.  Taxonomy and Classification: Essential for organizing life into hierarchical groups.  Evolutionary Studies: Understanding speciation and evolutionary relationships.  Practical Applications: o Agriculture: Identifying pest species and crop varieties. o Medicine: Understanding pathogens and their evolution. Conclusion The concept of a species is fundamental to biology, yet its definition varies based on context and criteria. Different species concepts—biological, morphological, ecological, phylogenetic, genetic, and evolutionary—offer unique perspectives, each with strengths and limitations. A holistic approach combining multiple concepts is often necessary to comprehensively understand and classify species. Classification of living things and domains of life 1. Introduction Classification in biology is the process of organizing living organisms into groups based on their similarities and evolutionary relationships. This system provides a framework to identify, name, and categorize organisms, making it easier to study and understand the vast diversity of life on Earth. 2. Historical Development of Classification  Aristotle's System (4th Century BCE): o Divided organisms into plants and animals based on their movement and habitat.  Carl Linnaeus (18th Century): o Introduced the binomial nomenclature system (Genus and species). o Proposed a hierarchical system: Kingdom, Phylum, Class, Order, Family, Genus, and Species.  Modern Classification: o Based on evolutionary relationships and genetic similarities. o Includes molecular and phylogenetic data. 3. Hierarchical Classification System The current system organizes life into a nested hierarchy: 1. Domain 2. Kingdom 3. Phylum 4. Class 5. Order 6. Family 7. Genus 8. Species 4. Domains of Life The concept of domains was introduced by Carl Woese in 1990 based on genetic and molecular analysis, particularly ribosomal RNA sequences. The three domains are: A. Domain Bacteria  Characteristics: o Prokaryotic (no nucleus or membrane-bound organelles). o Cell walls contain peptidoglycan. o Found in diverse environments, including soil, water, and inside other organisms.  Examples: o Escherichia coli, Streptococcus. B. Domain Archaea  Characteristics: o Prokaryotic, but genetically distinct from Bacteria. o Cell walls lack peptidoglycan; unique membrane lipids. o Often live in extreme environments (extremophiles), such as hot springs and salt lakes.  Examples: o Methanogens, Halophiles, Thermoacidophiles. C. Domain Eukarya  Characteristics: o Eukaryotic (cells with a nucleus and membrane-bound organelles). o Includes single-celled and multicellular organisms. o Further divided into four kingdoms: 1. Protista:  Mostly unicellular, some multicellular.  Examples: Amoeba, Paramecium. 2. Fungi:  Absorptive heterotrophs, cell walls made of chitin.  Examples: Mushrooms, Yeast. 3. Plantae:  Photosynthetic autotrophs, cell walls made of cellulose.  Examples: Mosses, Ferns, Flowering plants. 4. Animalia:  Multicellular heterotrophs, no cell walls.  Examples: Humans, birds, fish. 5. Kingdoms of life A. Monera (Prokaryotic organisms, now divided into Bacteria and Archaea). B. Protista (Simple eukaryotic organisms). C. Fungi (Decomposers with chitin cell walls). D. Plantae (Photosynthetic organisms). E. Animalia (Motile heterotrophs). 6. Importance of Classification 1. Organization: Helps organize vast biological diversity. 2. Evolutionary Insights: Reveals relationships among organisms. 3. Communication: Provides a universal language for scientists worldwide. 4. Conservation: Identifies species and ecosystems for protection. 5. Medical and Agricultural Applications: Identifying pathogens, crops, and beneficial organisms. 7. Modern Approaches to Classification Classification and the domains of life provide a framework for understanding the diversity and unity of living organisms. The three-domain system (Bacteria, Archaea, and Eukarya) reflects evolutionary relationships, while hierarchical classification organizes organisms into groups for better study and communication. With advancements in molecular biology, the system continues to evolve, offering deeper insights into life’s complexity.  Phylogenetics: o Based on evolutionary relationships and genetic data. o Uses tools like DNA sequencing to construct phylogenetic trees.  Molecular Taxonomy: o Involves the comparison of molecular structures (e.g., ribosomal RNA, proteins). Historical Geology and the Scale of Biological Time Historical geology is the study of Earth's history, focusing on the physical, chemical, and biological changes that have occurred over time. It examines the formation of Earth, the evolution of life, and the dynamic processes that have shaped the planet's surface. The concept of biological time, often represented through the geologic time scale, provides a framework to understand the major events in Earth's history and the progression of life. The Geologic Time Scale The geologic time scale is a chronological framework that divides Earth's history into eons, eras, periods, epochs, and ages. It reflects major geological and biological events. Major Divisions: 1. Eons (Largest unit): o Hadean (4.6–4.0 billion years ago):  Formation of Earth, molten surface, no life. o Archean (4.0–2.5 billion years ago):  Appearance of the first prokaryotic life (bacteria). o Proterozoic (2.5 billion–541 million years ago):  Rise of oxygen in the atmosphere; emergence of eukaryotes. o Phanerozoic (541 million years ago–Present):  Diversification of life; divided into eras. 2. Eras of the Phanerozoic: o Paleozoic Era (541–252 million years ago):  "Age of Fishes."  Explosion of marine life during the Cambrian period.  First land plants and animals. o Mesozoic Era (252–66 million years ago):  "Age of Reptiles."  Dominance of dinosaurs and emergence of mammals and birds.  Ended with a mass extinction (asteroid impact). o Cenozoic Era (66 million years ago–Present):  "Age of Mammals."  Diversification of mammals, birds, and flowering plants.  Rise of humans in the Quaternary period. 3. Periods, Epochs, and Ages: o Each era is divided into periods, which are further divided into epochs and ages. o For example, the Cenozoic Era includes the Quaternary Period, which contains the Holocene Epoch (current epoch). 3. Biological Milestones in Earth's History  4.0–3.8 Billion Years Ago: o Formation of the first life (prokaryotes). o Hypotheses: Abiogenesis in hydrothermal vents or shallow pools.  2.4 Billion Years Ago: o Great Oxidation Event: Oxygen accumulates in the atmosphere.  541 Million Years Ago: o Cambrian Explosion: Rapid diversification of complex life forms.  375 Million Years Ago: o First vertebrates transition to land (e.g., Tiktaalik).  252 Million Years Ago:  o Permian-Triassic extinction: Largest mass extinction, wiping out ~96% of species.  66 Million Years Ago: o Cretaceous-Paleogene extinction: Dinosaurs go extinct; mammals rise.  2.5 Million Years Ago: o Early humans (genus Homo) appear. 4. Scale of Biological Time Biological time is vast, spanning billions of years, and is represented using a logarithmic scale to visualize key events.  Relative Time: Establishes the order of events (e.g., older vs. younger rocks).  Absolute Time: Provides numerical ages (e.g., fossils dated to 65 million years). Visualizing the Geologic Time Scale: 1. Clock Model: Represents Earth's 4.6 billion years as a 24-hour clock. Humans appear in the last second. 2. Calendar Model: Earth's history compressed into a year. Multicellular life appears in November; humans arrive on December 31. 5. Importance of Historical Geology and Biological Time Historical geology and the geologic time scale provide a framework for understanding the Earth’s physical and biological evolution. By studying fossils, rock layers, and radiometric data, scientists unravel the story of Earth, from its fiery origins to the emergence of complex life, including humans. 1. Understanding Evolution: Reveals how life evolved and adapted to environmental changes. 2. Predicting Future Changes: Provides insights into current climate trends and mass extinction risks. 3. Natural Resources: Helps locate and extract fossil fuels, minerals, and groundwater. 4. Interdisciplinary Applications: Supports studies in paleontology, climatology, and ecology.