SB5.Students will evaluate the role of natural selection in the

development of the theory of evolution.SB5a.

Trace the history of the theory

Turn to p. 392 in your Biology textbook. List 10 facts about the “Earth’s Early History” section in your notebook. Be ready to

share in 8 minutes.

Before Life…Land Environments

Earth was molten when it formed about 4.6 billion years ago

After 500 million years, a solid crust formed

Too much heat for life to exist

Before Life…Atmosphere

Gases in atmosphere came from volcanoes

Water vapor, carbon dioxide, methane, ammonia gas, nitrogen, hydrogen, etc.

The early atmosphere was anaerobic (it had little or no free oxygen).

Where did the first living things come from?

ORIGINS: Early IdeasSpontaneous Generation: Life arises from nonlife

Proposed by Aristotle (384-322 BC)

Also called abiogenesis

Ex: Place damp hay and corn in a corner, and mice would be created.

ORIGINS: Early IdeasSpontaneous Generation Experiments

Francisco Redi (1668) showed that flies and maggots did not spontaneously come from rotting meat.

ORIGINS: Early IdeasSpontaneous Generation Experiments

Lazzaro Spallanzani(1765) boiled nutrient solutions in flasks.

Lazzaro Spallanzani’s Experiment

People did not reject the theory until mid-1800s when it was replaced by the Theory of Biogenesis.

ORIGINS: Early IdeasTheory of Biogenesis: Only living organisms can produce other living organisms.

Louis Pasteur-designed an experiment to show that biogenesis occurred in microorganisms

If life can arise only from pre-existing life, then how did the first life form appear?

ORIGINS: Modern Ideas Life originated through a series of early chemical

events.

Simple organic moleculescomplex organic moleculessimple metabolic pathwaysemergenceof life

Stanley Miller & Harold Urey (1953) were the first to show that simple organic compounds (macromolecules) could be made from inorganic compounds.

ORIGINS: Modern IdeasMiller & Urey’s Experiment

Filled apparatus with water and gases from early atmosphere

Electric discharges simulate lightning for energy

Resulting mixture contained organic compounds including amino acids.

ORIGINS: Modern Ideas The first cells were anaerobic prokaryotes.

Eukaryotic cells first appeared about 1.8 billion years ago when oxygen became a part of the Earth’s atmosphere.

Endosymbiosis: a type of symbiosis in which one organism lives inside the other, the two typically behaving as a single organism

The hot springs of Yellowstone National Park, USA, were among the first

places Archaea were discovered. The biologists are immersing microscope slides in the boiling pool

onto which some archaeansmight be captured for

study.

ORIGINS: Modern IdeasThe Endosymbiont Theory

Proposed by Lynn Margulis in 1966

The ancestors of eukaryotic cells lived in association with prokaryotic cells.

Evidence for the Endosymbiont Theory

Mitochondria and chloroplasts:

have their own DNA (circular like prokaryotic DNA)

have ribosomes resembling prokaryotic cells

reproduce by fission, independent of the rest of cell

ORIGINS: Modern IdeasOther Ideas

Organic reactions began in deep sea vents (hot, volcanic)

Meteorites brought the first organic molecules to Earth

Quick Review1. Differentiate

between spontaneous generation and biogenesis.

2. Describe the endosymbionttheory.