key concept specific environmental conditions are necessary in order for fossils...
TRANSCRIPT
12.1 The Fossil Record
KEY CONCEPT
Specific environmental conditions are necessary in
order for fossils to form.
12.1 The Fossil Record
Fossils can form in several ways.
• Permineralization occurs when minerals carried by water
are deposited around a hard structure.
12.1 The Fossil Record
• A natural cast forms when flowing water removes all of the
original tissue, leaving an impression.
12.1 The Fossil Record
• Trace fossils record the activity of an organism.
12.1 The Fossil Record
• Amber-preserved fossils are organisms that become
trapped in tree resin that hardens after the tree is buried.
12.1 The Fossil Record
• Preserved remains form when an entire organism becomes
encased in material such as ice.
12.1 The Fossil Record
• Specific conditions are needed for fossilization.
• Only a tiny percentage of living things became fossils.
12.1 The Fossil Record
Radiometric dating provides an accurate way to estimate
the age of fossils.
• Relative dating estimates the time during which an
organism lived.
– It compares the placement
of fossils in layers of rock.
– Scientists infer the order in
which species existed.
12.1 The Fossil Record
• Radiometric dating uses decay of unstable isotopes.
– Isotopes are atoms of an element that differ in their
number of neutrons.
neutrons protrons
12.1 The Fossil Record
– A half-life is the amount of time it takes for half of the
isotope to decay.
• Radiometric dating uses decay of unstable isotopes.
– Isotopes are atoms of an element that differ in their
number of neutrons.
12.2 The Geologic Time Scale
KEY CONCEPT
The geologic time scale divides Earth’s history based
on major past events.
12.2 The Geologic Time Scale
Index fossils are another tool to determine the age of rock
layers.
• Index fossils can provide the relative age of a rock layer.
– existed only during specific spans of time
– occurred in large geographic areas
• Index fossils include fusulinids and trilobites.
12.2 The Geologic Time Scale
The geologic time scale organizes Earth’s history.
• The history of Earth is
represented in the geologic time
scale.
100
250
550
1000
2000
PRECAMBRIAN TIME
Cyanobacteria
This time span makes up the
vast majority of Earth’s history.
It includes the oldest known
rocks and fossils, the origin of
eukaryotes, and the oldest
animal fossils.
12.2 The Geologic Time Scale
• Eras last tens to hundreds of millions of years.
– consist of two or more periods
– three eras: Cenozoic, Mesozoic, Paleozoic
12.2 The Geologic Time Scale
• Periods last tens of millions of years.
– most commonly used units of time on time scale
– associated with rock systems.
• Epochs last several
million years.
12.3 Origin of Life
KEY CONCEPT
The origin of life on Earth remains a puzzle.
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.
– Miller-Urey experiment
– meteorite hypothesis
electrodes
heat source amino acids
water
“atmosphere”
“ocean”
12.3 Origin of Life
• There are different hypotheses of early cell structure.
– iron-sulfide bubbles hypothesis
12.3 Origin of Life
• There are different hypotheses of early cell structure.
– lipid membrane hypothesis
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.
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.
• The oldest known fossils are a group of marine
cyanobacteria.
– prokaryotic cells
– added oxygen to
atmosphere
– deposited minerals
12.4 Early Single-Celled Organisms
• Fossil stromatolites provide evidence of early colonies of
life.
12.4 Early Single-Celled Organisms
Eukaryotic cells may have evolved through
endosymbiosis.
• 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
The evolution of sexual reproduction led to increased
diversity.
• Genetic variation is an advantage of sexual reproduction.
• Sexual reproduction may have led to the evolution of
multicellular life.
12.5 Radiation of Multicellular Life
KEY CONCEPT
Multicellular life evolved in distinct phases.
12.5 Radiation of Multicellular Life
Life moved onto land during the Paleozoic Era.
• Multicellular organisms first
appeared during the
Paleozoic era.
• The era began 544 million
years ago and ended 248
million years ago.
• The Cambrian explosion led
to a huge diversity of animal
species.
12.5 Radiation of Multicellular Life
• Life moved onto land in the middle of the Paleozoic era.
12.5 Radiation of Multicellular Life
Reptiles radiated during the Mesozoic era.
• The Mesozoic era is known as the Age of Reptiles.
• It began 248 million years ago and ended 65 million years
ago.
• Dinosaurs, birds, flowering plants, and first mammals
appeared.
12.5 Radiation of Multicellular Life
Mammals radiated during the Cenozoic era.
• The Cenozoic era began 65 million years ago and continues today.
• Placental mammals and monotremes evolved and diversified.
• Anatomically modern humans appeared late in the era.
12.6 Primate Evolution
KEY CONCEPT
Humans appeared late in Earth’s history.
12.6 Primate Evolution
Humans share a common ancestor with other primates.
• Primates are mammals with flexible hands and feet,
forward-looking eyes and enlarged brains.
12.6 Primate Evolution
• Primates evolved into prosimians and anthropoids.
– Prosimians are the oldest living primates.
– They are mostly small and nocturnal.
12.6 Primate Evolution
– They are subdivided into the New World monkeys, Old
World monkeys, and hominoids.
– Anthropoids are humanlike primates.
– Homonoids are
divided into
hominids, great
apes, and lesser
apes.
– Hominids include
living and extinct
humans.
12.6 Primate Evolution
• Bipedal means walking on two legs.
– foraging
– carrying infants and food
– using tools
• Walking upright has
important adaptive
advantages.
12.6 Primate Evolution
There are many fossils of extinct hominids.
• Most hominids are either the genus Australopithecus or
Homo.
• Australopithecines were a successful genus.
• The Homo genus first evolved 2.4 million years ago.
12.6 Primate Evolution
Modern humans arose about 200,000 years ago.
• Homo sapiens fossils date to 200,000 years ago.
• Human evolution is influenced by a tool-based culture.
• There is a trend toward increased brain size in hominids.
Australopithecus
afarensis
Homo habilis Homo
neanderthalensis
Homo sapiens