Download HISTORY OF LIFE 14.1 Fossil Evidence of Change I. Land

HISTORY OF LIFE
14.1 Fossil Evidence of Change
I. Land Environments
A. Earth formed about 4.6 billion years ago.
B. Earth was molten when it formed
C. The crust hardened about 500 million years later
D. Gravity pulled the densest elements to the center of the planet
II. Atmosphere
A. The gases that made up the early atmosphere are those expelled by volcanoes.
1. Water vapor (H2O)
2. Carbon dioxide (CO2)
3. Sulfur dioxide (SO2)
4. Carbon monoxide (CO)
5. Hydrogen sulfide (H2S)
6. Hydrogen cyanide (HCN)
7. Nitrogen (N2)
8. Hydrogen (H2)
B. Crust cooled
C. Oceans formed as the atmosphere cooled
D. First signs of life showed up around 3.5 billion years ago
III. Clues in Rocks
A. A fossil is any preserved evidence of an organism.
B. Most organisms decompose before they have a chance to become fossilized.
C. Very few organisms become fossils.
D. This means there could be millions of creatures that are extinct that we will never know
about
IV. Fossil Formation
A. Nearly all fossils are formed in sedimentary rock.
B. The sediments build up until they cover the organism’s remains and organic matter fills empty
pore spaces of organisms.
V. Dating Fossils
A. Relative dating is a method used to determine the age of rocks by comparing them with those
in other layers.
oldest
VI. The Geologic Time Scale
A. The geological time scale is a model that expresses the major geological and biological events
in Earth’s history.
B. Plate tectonics describes the movement of several large plates that make up the surface of
Earth.
C. Also known as continental drift.
14.2 The Origin of Life
I. Origins: Early Ideas
A. Spontaneous generation is the idea that life arises from nonlife
B. Francesco Redi, an Italian scientist, tested the idea that flies arose spontaneously from
rotting meat
C. The theory of biogenesis states that only living organisms can produce other living organisms.
Louis Pasteur designed an experiment to show that biogenesis was true even for
microorganisms
II. Origins: Modern Ideas
A. Simple organic molecule formation
B. The primordial soup hypothesis was an early hypothesis about the origin of life.
C. Organic molecules could have been synthesized from simple reactions.
D. UV light from the Sun and electric discharge in lightning might have been the primary energy
sources.
E. Stanley Miller and Harold Urey were the first to show that simple organic molecules could be
made from inorganic compounds
F. Later, scientists found that hydrogen cyanide could be formed from even simpler molecules
in simulated early Earth environments.
III. Making Proteins
A. Life requires proteins
1. One possible mechanism for the formation of proteins would be if amino acids were bound to
a clay particle.
IV. Genetic Code
A. Some RNA sequences appear to have changed very little through time.
B. Many biologists consider RNA to have been life’s first coding system.
C. Other researchers have proposed that clay crystals could have provided an initial template for
RNA replication.
V. Cellular Evolution
A. Scientists hypothesize that the first cells were prokaryotes.
B. Many scientists think that modern prokaryotes called archaea are the closest relatives of
Earth’s first cells.
VI. Photosynthesizing Prokaryotes
A. Archaea are autotrophic.
B. They do NOT obtain their energy from the Sun.
C. Archaea also do not need or produce oxygen.
D. Many scientists think that photosynthesizing prokaryotes evolved not long after the archaea.
E. Prokaryotes, called cyanobacteria, have been found in rocks as old as 3.5 billion years.
VII. The Endosymbiont Theory
A. The ancestors of eukaryotic cells lived in association with prokaryotic cells.
B. The relationship between the cells became mutually beneficial, and the prokaryotic
symbionts became organelles in eukaryotic cells.
C. This theory explains the origin of chloroplasts and mitochondria