Ch. 15 EvolutionSection 1: Origin of Life

How did life on Earth begin?

Let’s first start with a small discussion that relates to this chapter. Raise your hand and let me know your opinion(s) on any of the following questions.

How did our universe begin?How did life begin on Earth?

Where did our human ancestors come from?

4 processes needed for life on Earth:

1. ORGANIC MOLECULES - When Earth was formed, it consisted of rock, minerals, gases, and water….so where did the organic molecules come from?

2. ABILITY TO FORM POLYMERS - Furthermore, monomers (basic organic molecules like amino acids and monosaccharides) are not enough to make complex organisms, these molecules must first combine to become polymers

4 processes needed for life on Earth:

3. ABILITY TO REPRODUCE - Organisms must self-replicate, but early organisms most likely did not have “modern” DNA or RNA or the enzymes necessary to carry out the functions

4. PACKAGING MOLECULES IN MEMBRANES - Earth had water, but the presents of water often makes polymers break down into monomers (hydrolysis reactions) … this makes it hard to make and keep complex molecules

Miller Urey Experiment • Experiment performed by Stanley Miller and Harold Urey at

the University of Chicago 1953

•Added gases that they thought would have been present on ancient Earth including methane, hydrogen, ammonia•Added water, which was heated and cooled to simulate water cycle•Exposed apparatus to UV radiation since no ozone layer yet•Electric sparks simulated lightening

Results of Experiment

• After one week, organic compounds such as amino acids had formed as well as certain sugars and nucleic acids

• This helps explain the potential of how the first organic molecules formed, but we are still left with the other 3 problems including complex organic molecules, self-replicating molecules, and the membrane dilemma

Potential Locations of Synthesis of Organic Molecules:

1. In space• scientists have studied spectral lines of distant

clouds of dust particles and have spotted glycine (simplest amino acid)

• Further studies in low pressure, low temp environments have led to synthesis of amino acids

• Also idea that comets could have brought amino acids in massive bombardment ~ 4 bya

• Idea that organic molecules may have come from space is called Panspermia

2. In alternating wet and dry conditions• Areas like seashores, flood plains, intertidal zones (ex: famous ancient fossil of stromatolites found in

intertidal areas; helps to suggest that these conditions were favorable to ancient life)

3. Near volcanoes• Has necessary gases including

water vapor as well as a warm environment

4. Near hydrothermal vents• The vents release hot water,

minerals from Earth’s crust, and gases