2 How Did Life Begin? The ideas presented here are hypotheses. The evidence for life’s origin’s are speculative and difficult to find (since these events occurred much further back in Earth’s history)
3 Early EarthEarly Scientists hypothesized that the Earth’s early atmosphere was rich in ammonia, methane, water vapor, and hydrogen.Earth’s atmosphere lacked oxygen
4 How Did Life Begin? Step 1: Formation of the building blocks of life Step 2: Formation of cellsStep 3: Formation of a reliable CODE for building proteins
5 Step 1: Formation of the Building Blocks of Life Can the components of living organisms form all by themselves from simple chemicals? YESThe Miller-Urey experiment demonstrated how cells formed all by themselves.
6 Step 1: Formation of the building blocks of life Miller-Urey Experiment:Miller and Urey placed Ammonia, Water, Methane, and Hydrogen gases into a device.To simulate lightening they used electrical sparks. Heat could also be usedThey found organic molecules in the device after 3 days. (fats/lipids & amino acids).
7 Step 1: Formation of the building blocks of life
8 Step 2: Formation of cells The Miller-Urey experiment did NOT yield living organisms … so how did the first cells form?Experiments show that membranes can form by themselves when lipids (fats) are added to water.
9 Step 3: Formation of a reliable CODE for building proteins Cells may have formed on their own, but eventually cells would need to replicate and pass on their ability to make proteins to offspring cells.Some evidence exists that theearliest code for building proteinsmay have been an RNA code.
10 Step 3: Formation of a reliable CODE for building proteins RNA can code for building proteins as well as serving as enzymes to speed up other reactions.Later, a DNA code developed whichwas more stable and held the proteincode longer.
11 History of Life On Earth 19.3 Earth is 4.6 billion years oldFossil evidence indicates that the earliest life on Earth might have existed 3.5 billion years ago…………Suggesting that it took approximately 1.1 billion years for life to evolve
12 Oldest FossilsStramatolites or mats of Cyanobacteria
13 History of Life On Earth The earliest life forms on Earth were prokaryotic.(before the nucleus)They were also almost certainly heterotrophs early on.
14 Early History of Life Can Be Characterized By 3 Developments Development #1: AutotrophyDevelopment #2: Evolution of Eukaryotic cellsDevelopment #3: Evolution of Multicellular Organisms
15 Development #1: Autotrophy Autotrophs make their own food by the process of photosynthesis.The byproduct that autotrophs release into the atmosphere is oxygen.
16 Development #1: Autotrophy Cyanobacteria were photosynthetic organisms that began adding oxygen to the atmosphere.
17 Development #1: Autotrophy Over time oxygen built up in the atmosphere, eventually forming the Ozone Layer O3The Ozone Layer blocked UV rays to allow for land life
18 Development #2: Evolution of Eukaryotic Cells The evolution of some eukaryotic organelles such as chloroplasts and mitochondria can be explained by the endosymbiotic theory.
19 Development #2: Evolution of Eukaryotic Cells Endosymbiotic Theory:Large Prokaryotic Cells engulfed Smaller aerobic bacteria and cyanobacteria, which then began to live inside the larger cells.Aerobic bacteria are thought to give rise to the mitochondria.Cyanobacteria (contain chlorophyll) are thought to give rise to chloroplasts.
21 Development #2: Evolution of Eukaryotic Cells Evidence that supports the Endosymbiotic Theory:Size & Structure: Mitochondria & Chloroplasts are the same size as most bacteriaGenetic Material: Mitochondria & Chloroplasts contain DNA different from the nucleusReproduction: Mitochondria and Chloroplasts reproduce similarly to bacteria (binary fission)
22 Development #3: Evolution of Multicellular Organisms Only organisms made of eukaryotic cells can be multicellularMulticellularity first developed in protists in Precambrian Time