Transcript 12.1 The Fossil Record

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
• Radiometric dating uses decay of unstable isotopes.
– Isotopes are atoms of an element that differ in their
number of neutrons.
– A half-life is the amount of time it takes for half of the
isotope to decay.
12.3
of Life Record
12.1- Origin
The Fossil
KEY CONCEPT
The origin of life on Earth remains a puzzle.
12.3
of Life Record
12.1- Origin
The Fossil
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.
• The cloud and dust
condensed forming our
solar system. (4.6 bya)
12.3
of Life Record
12.1- Origin
The Fossil
Several sets of hypotheses propose how life began on
Earth.
• There are two organic molecule hypotheses.
– Miller-Urey experiment (in put of energy from lightening)
electrodes
“atmosphere”
water
“ocean”
heat source
amino acids
– meteorite hypothesis (brought organic compounds)
12.3
of Life Record
12.1- Origin
The Fossil
• There are different hypotheses of early cell structure.
– iron-sulfide bubbles hypothesis
12.3
of Life Record
12.1- Origin
The Fossil
• There are different hypotheses of early cell structure.
– lipid membrane hypothesis, lipids spontaneously made a
cell membrane
12.3
of Life Record
12.1- Origin
The Fossil
• 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
Organisms
12.1- Early
The Single-Celled
Fossil Record
KEY CONCEPT
Single-celled organisms existed 3.8 billion years ago.
12.4
Organisms
12.1- Early
The Single-Celled
Fossil Record
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
Organisms
12.1- Early
The Single-Celled
Fossil Record
• Fossil stromatolites provide evidence of early colonies of
life. (contain cyanobacteria)
12.4
Organisms
12.1- Early
The Single-Celled
Fossil Record
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.
12.6
Evolution
12.1- Primate
The Fossil
Record
KEY CONCEPT
Humans appeared late in Earth’s history.
12.6
Evolution
12.1- Primate
The Fossil
Record
Humans share a common ancestor with other primates.
• Primates are mammals with flexible hands and feet,
forward-looking eyes and enlarged brains.
12.6
Evolution
12.1- Primate
The Fossil
Record
• Primates evolved into prosimians and anthropoids.
– Prosimians are the oldest living primates.
– They are mostly small and nocturnal.
12.6
Evolution
12.1- Primate
The Fossil
Record
– Anthropoids are humanlike primates.
– They are subdivided into the New World monkeys, Old
World monkeys, and hominoids.
– Homonoids are
divided into
hominids, great
apes, and lesser
apes.
– Hominids include
living and extinct
humans.
12.6
Evolution
12.1- Primate
The Fossil
Record
Hominids Characteristics:
• Bipedal means walking on two legs.
– foraging
– carrying infants and food
– using tools
• Walking upright has
important adaptive
advantages.
12.6
Evolution
12.1- Primate
The Fossil
Record
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
Evolution
12.1- Primate
The Fossil
Record
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