The Origin and Early

Evolution of Life

Chapter 18

Learning Objectives

1. Differentiate between chemical evolution and organic evolution.

2. Describe the conditions on the primitive earth predicted by laboratory experiments that favored the spontaneous development of organic molecules.

3. Explain the probable sequence in the origin of the first cells, and describe how this cell interacted with its environment.

4. Review the theories proposed to explain the origin of eukaryotic organelles.

The Big Bang

• 12-15 billion years ago all

matter in the universe was

compressed into a mass

the size of our sun

• Sudden instantaneous explosion of matter and energy throughout the known universe

Earth Forms• About 4.6 to 4.5 billion years ago• Minerals and ice orbiting the sun

started clumping together• Heavy minerals moved to Earth’s

interior, lighter minerals floated to surface– Produced outer crust and

inner mantle• Chemical evolution produced the

primordial sea and the early atmosphere that would support the biosphere of the future.

p. 288

Earth Is “Just Right” for Life

The Planet:

• If smaller in diameter, gravity would not be great enough to hold onto atmosphere

• If closer to sun, water would have evaporated

• If farther from sun, water (the solvent of life) would have been locked up as ice

Early Atmosphere:

• Hydrogen gas

• Nitrogen

• Carbon monoxide

• Carbon dioxide

• No gaseous oxygen

p. 288

Stanley Miller’s Experiment

• Mixed methane, hydrogen, ammonia, and water

• Simulated lightning• Amino acids and

other small molecules formed

What, at a minimum, is needed to form a cell-like structure from these molecules?

p. 289

Possible Sequence

START: “Chemical Evolution”

“Organic Evolution”

informational molecules

separation of environments

ENDp. 291

Why is RNA believed to be the first genetic information?

Why is DNA a better molecule for heredity?

The First Cells

• Prokaryotic heterotrophs

Describe what this means.

• Secured energy through

anaerobic metabolism

…Describe.

– No oxygen present

…Why not?

p. 291Is there fossil evidence for these first cells?

Fossil Evidence• photosynthetic eubacteria

• Oxygen producing

• permits aerobic respiration

3.5 bya

2.1 bya 1.2 byap. 292

Possible Origin of ER & Nuclear Envelope

DNA

infolding of plasma membrane

p. 294

aka: Autogenous Theory

Endosymbiotic Theory

Cyanophora paradoxa

p. 295