12.3 Origin of Life

KEY CONCEPT The origin of life on Earth remains a puzzle.

12.3 Origin of Life

NGSSS

•SC.912.L.15.8 Describe the scientific explanations of the origin of life on Earth. (MODERATE)

12.3 Origin of Life

Earth was very different billions of years ago.

• There have been many hypotheses of Earth’s origins.• The most widely accepted hypothesis of Earth’s origins is

the nebula hypothesis.

12.3 Origin of Life

Several sets of hypotheses propose how life began on Earth.

• There are two organic molecule hypotheses.

1.Miller-Urey experiment- Demonstrated that organic compounds could be made by passing a electric current (simulating lightning) through a closed system that held a mixture of gasses and water.

electrodes

heat source amino acids

water

“atmosphere”

“ocean”

• Gasses thought to be on early earth: ammonia, methane, hydrogen, Carbon dioxide.

• No oxygen

12.3 Origin of Life

There are two organic molecule hypotheses.

2. meteorite hypothesis- Amino acids may have arrived on Earth through meteorites or asteroid impact.

12.3 Origin of Life

• There are different hypotheses of early cell structure.

– iron-sulfide bubbles hypothesis- Biological molecule combined in in compartments of hydrothermal vents where organic molecules were concentrated - the walls of the compartment formed the cell membranes.

12.3 Origin of Life

• There are different hypotheses of early cell structure.– lipid membrane hypothesis- lipid spheres could form

around a variety of organic molecules.

12.3 Origin of Life

• A hypothesis proposes that RNA was the first genetic material.

– Ribozymes are RNA molecules that catalyze their own replication.

– DNA needs enzymes to replicate itself.