Transcript Chapter 7 - TeacherWeb

Chapter 7
The Evolution of Living Things
Diatryma and the Rooster
• Diatryma weighed about 400
pounds (182 kg.)
• Flightless
• Cenozoic Era (57-35) million
years ago
• Over 6 feet tall
• Enormous Beak
• Sharp Claws
• Distant relative of the chicken
Frog Crazy
Adaptation
Adaptation – a characteristic that helps an
organism survive and reproduce in its
environment
Adaptations Include Structures and Behaviors for:
1) finding food
2) protection
3) moving from place to place
Species
Species – a group of organisms that can mate with
one another to produce fertile offspring
Do Species Change over Time?
• Millions of different species occupy the Earth, ranging
from bacteria to fungi to plants and animals.
• Have these same species always existed on Earth?
The Earth is 4.6 Billion Years Old
• Over that
period of time
the Earth has
changed
dramatically.
Human existence is less than a hairs
width at the end of the diagram
How do we estimate the age of the
Earth?
• Radioactive Decay of Earth’s Rocks
• Moon Rocks
• Meteorites
• Radiometric Dating of Earth’s
Rocks- The ages of Earth
rocks are measured by the
decay of long-lived radioactive
isotopes of elements that occur
naturally in rocks and minerals
and that decay with half lives
of 700 million to more than
100 billion years to stable
isotopes of other elements.
Used to measure the last time
that the rock being dated was
melted.
Moon Dating
• The Moon is a more primitive planet
than Earth because it has not been
disturbed by plate tectonics; thus, some
of its more ancient rocks are more
plentiful. Only a small number of rocks
were returned to Earth by the six Apollo
and three Luna missions. These rocks
vary greatly in age, a reflection of their
different ages of formation and their
subsequent histories. The oldest dated
moon rocks, however, have ages
between 4.4 and 4.5 billion years and
provide a minimum age for the
formation of our nearest planetary
neighbor.
Meteorite Dating
• Thousands of meteorites, which are fragments of asteroids that
fall to Earth, have been recovered. These primitive objects
provide the best ages for the time of formation of the Solar
System. There are more than 70 meteorites, of different types,
whose ages have been measured using radiometric dating
techniques. The results show that the meteorites, and therefore
the Solar System, formed between 4.53 and 4.58 billion years
ago.
• The best age for the Earth comes not from dating individual
rocks but by considering the Earth and meteorites as part of the
same evolving system
Evidence for an old universe:
Absence of short lived stars from star clusters 14-18 Ga1
Length it takes light to get to the earth from the most distant
objects in the universe (10 Ga)2
Hubble expansion of the universe 7 - 20 Ga1
Evidence for an old solar system
Age of meteorites 4.4-4.6 Ga (isochron method)1
Age of moon 4.5 Ga (radiometric)1
Earth-meteorite system 4.54 Ga (lead isotope age)1
Evidence for an old earth:
Earths oldest rocks 3.8-3.9 Ga (radiometric)1
Evolution
Evolution – the process by which populations
accumulate inherited changes over time.
* Because of evolution scientists think that all living
things and once living things, from daisies to
crocodiles to humans share a common ancestor.
The Evidence for Evolution
• Comparative Anatomy – comparing similar
structures in different organisms.
• Fossils – the solidified remains or imprints of once
living organisms.
• Embryonic Anatomy
• Vestigial Structures
– The fossil record –provides a historical sequence of
evolution and life.
•
Fossilization
Paleontology - the study
of the past through the
study of fossils.
The fossil is a rock - Often the
remains of preserved organisms
are not of the organism itself but
instead of minerals deposited
where, especially, hard parts of
the organism previously existed.
Soft parts tend not to
fossilize because they
usually decay prior to
mineralization.
However, soft parts, under
the right conditions, can
also make impressions.
Included among such
imprints are those made
during the act of locomotion
such as fossil foot prints or
various invertebrate trails
A once living organism
The organism dies
The soft parts decay
The organism is quickly
covered in sediment
The hard parts make a
mold (hollow impression)
which is replaced by minerals
There are six ways that organisms can
turn into fossils, including:
1) unaltered preservation (like insects or
plant parts trapped in amber, a hardened
form of tree sap)
2) permineralization=petrification (in which
rock-like minerals seep in slowly and
replace the original organic tissues,
forming a rock-like fossil - can preserve
hard and soft parts - most bone and wood
fossils are permineralized)
3) replacement (An organism's hard parts
dissolve and are replaced by other
minerals.
4) carbonization=coalification
5) recrystalization
6) authigenic preservation
Most animals did not fossilize; they simply
decayed and were lost from the fossil record.
Paleontologists estimate that only a small
percentage of the dinosaur genera that ever lived
have been or will be found as fossils.
Ways of Dating Fossils
• Relative Dating
• Direct Dating
•
Relative dating
Uses sediment
positional information
– the relative positions
of layers of sediment
determine the age of the
fossils found within them.
•
Crucial assumptions:
–
older layers are buried beneath younger layers (unless the rock
itself has been flipped by geologic forces)
–
fossils are found within the layer that formed contemporaneously
with the death of the fossilized organism (an assumption which is
obviously not necessarily true for organisms which tend to burrow
in sediment)
Direct dating
•
Radioisotope clocks:
–
Carbon 14 dating
Non-radioisotope methods of direct dating:
– Other methods of direct dating include:
» tree ring comparisons
» magnetic alignment with the earth's magnetic pole (which
tends to switch from North to South from time to time;
known as paleomagnitism)