12.3 Origin of Life

KEY CONCEPT The origin of life on Earth is a topic that has generated great amounts of study.

12.3 Origin of Life

Earth was very different billions of years ago. Name some differences that you know. • There have been many hypotheses of Earth’s origins.• The most widely accepted hypothesis of Earth’s origins is

the nebula hypothesis.

A swirling cloud of gas was drawn together due to gravity, forming our sun. Remaining debris circled the sun and, through repeated collisions, formed the planets.

12.3 Origin of Life

Several sets of hypotheses propose how life began on Earth.

• There are two organic molecule hypotheses.– Miller-Urey experiment

– meteorite hypothesis

electrodes

heat source amino acids

water

“atmosphere”

“ocean”

• Passing an electric charge through the gases present in early Earth formed amino acids needed for life

Amino acids were found on a meteorite that fell in Australia in 1969.

12.3 Origin of Life

• There are different hypotheses of early cell structure.– iron-sulfide bubbles hypothesis

– Biological molecules combined in the compartments of these chimneys with the compartment walls acting as the first cellular membranes.

12.3 Origin of Life

• There are different hypotheses of early cell structure.– lipid membrane hypothesis

– Lipid molecules spontaneously form membrane-enclosed spheres.

– Forming around organic molecules could result in structures that would give rise to the first cells

12.4 Early Single-Celled Organisms

KEY CONCEPT Single-celled organisms existed 3.8 billion years ago.

12.4 Early Single-Celled Organisms

Microbes have changed the physical and chemical composition of Earth. How?

• The oldest known fossils are a group of marine cyanobacteria. – prokaryotic cells– added oxygen to

atmosphere– deposited minerals

Symbiosis

• What is symbiosis?

• If two organisms become so dependent upon each other that they cannot survive alone, is it possible they could merge into one life form?

• What if it becomes more advantageous to the survival of the offspring if both organisms multiply at the same time?

12.4 Early Single-Celled Organisms

Eukaryotic cells may have evolved through endosymbiosis. Break it down… what do you think endosymbiosis means?• Endosymbiosis is a relationship in which one organism lives

within the body of another.• Mitochondria and chloroplasts may have developed through

endosymbiosis.

12.4 Early Single-Celled Organisms

Why are geologists able to estimate the age of rock strata using index fossils?

• A. Index fossils formed only in certain kinds of rocks. • B. Two methods of dating need to be used to date rock strata. • C. The organisms that formed index fossils lived for long periods of

time. • D. The organisms that formed index fossils lived only during a

specific time period.

12.4 Early Single-Celled Organisms

Why are geologists able to estimate the age of rock strata using index fossils?

• A. Index fossils formed only in certain kinds of rocks. • B. Two methods of dating need to be used to date rock strata. • C. The organisms that formed index fossils lived for long periods of

time. • D. The organisms that formed index fossils lived only during a

specific time period.

Correct Answer = D

During which period did all existing animal phyla develop? • A. Devonian • B. Triassic • C. Cambrian • D. Jurassic

12.4 Early Single-Celled Organisms

Why are geologists able to estimate the age of rock strata using index fossils?

• A. Index fossils formed only in certain kinds of rocks. • B. Two methods of dating need to be used to date rock strata. • C. The organisms that formed index fossils lived for long periods of

time. • D. The organisms that formed index fossils lived only during a

specific time period.• Correct Answer = D

During which period did all existing animal phyla develop? • A. Devonian • B. Triassic • C. Cambrian • D. Jurassic• Correct Answer = C

12.4 Early Single-Celled Organisms

What events help geologists define where one period ends and another begins?

• A. Adaptive extinctions • B. Mass extinctions • C. Major earthquakes • D. Bursts of radioactivity from the Sun

12.4 Early Single-Celled Organisms

What events help geologists define where one period ends and another begins?

• A. Adaptive extinctions • B. Mass extinctions • C. Major earthquakes • D. Bursts of radioactivity from the Sun • Correct Answer = B

12.4 Early Single-Celled Organisms

Review

• The nebula hypothesis – our solar system arose from a condensing nebula

• There are different theories as to how the first amino acids came to be– The Miller-Urey experiment resulted in amino acids being formed

after passing electricity through gases– The meteorite hypothesis suggests that the original amino acids

came from outer space• There are different theories as to how the first cells formed

– Iron sulfide bubbles theory– Lipid membrane theory

• Cyanobacteria are the oldest fossils and may have given the concentrations of oxygen needed for sustaining life on Earth

• Eukaryotic cells may have arisen from endosymbiosis