Early Origins Chapter 19.1 & 19.3

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)

Early Earth Early Scientists hypothesized that the Earth’s early atmosphere was rich in ammonia, methane, water vapor, and hydrogen. Earth’s atmosphere lacked oxygen

How Did Life Begin? Step 1: Formation of the building blocks of life Step 2: Formation of cells Step 3: Formation of a reliable CODE for building proteins

Step 1: Formation of the Building Blocks of Life Can the components of living organisms form all by themselves from simple chemicals? YES The Miller-Urey experiment demonstrated how cells formed all by themselves.

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 used They found organic molecules in the device after 3 days. (fats/lipids & amino acids).

Step 1: Formation of the building blocks of life

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.

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 the earliest code for building proteins may have been an RNA code.

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 which was more stable and held the protein code longer.

History of Life On Earth 19.3 Earth is 4.6 billion years old Fossil 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

Oldest Fossils Stramatolites or mats of Cyanobacteria

History of Life On Earth The earliest life forms on Earth were prokaryotic.(before the nucleus) They were also almost certainly heterotrophs early on.  

Early History of Life Can Be Characterized By 3 Developments Development #1: Autotrophy Development #2: Evolution of Eukaryotic cells Development #3: Evolution of Multicellular Organisms

Development #1: Autotrophy Autotrophs make their own food by the process of photosynthesis. The byproduct that autotrophs release into the atmosphere is oxygen.

Development #1: Autotrophy Cyanobacteria were photosynthetic organisms that began adding oxygen to the atmosphere.

Development #1: Autotrophy Over time oxygen built up in the atmosphere, eventually forming the Ozone Layer O3 The Ozone Layer blocked UV rays to allow for land life

Development #2: Evolution of Eukaryotic Cells The evolution of some eukaryotic organelles such as chloroplasts and mitochondria can be explained by the endosymbiotic theory.

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.

Development #2: Evolution of Eukaryotic Cells Evidence that supports the Endosymbiotic Theory: Size & Structure: Mitochondria & Chloroplasts are the same size as most bacteria Genetic Material: Mitochondria & Chloroplasts contain DNA different from the nucleus Reproduction: Mitochondria and Chloroplasts reproduce similarly to bacteria (binary fission)

Development #3: Evolution of Multicellular Organisms Only organisms made of eukaryotic cells can be multicellular Multicellularity first developed in protists in Precambrian Time

The End