Transcript Evidence for Evolution

Evidence for Evolution
Distribution and Fossils
Distribution
The distribution of living things on the
globe provides information about the
past histories of both living things and
the surface of the Earth. This evidence
is consistent not just with the evolution
of life, but also with the movement of
continental plates around the worldotherwise known as plate tectonics.
Plate Tectonics
Marsupials
• Marsupials are a group of mammals that
give birth to small young who develop
inside a pouch
• They evolved early in the history of
mammals
• Placental mammals, those that gestate
young in the uterus, evolved from
marsupials
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Which organism would have the advantage?
Marsupial or Placental Mammal?
Why?
Marsupial Distribution
Can You Explain Current
Marsupial Distribution?
Methods of Dating
Absolute and Relative
How to measure age
• A numerical (or "absolute")
age is a specific number of
years, like 150 million years
ago. A relative age simply
states whether one rock
formation is older or younger
than another formation.
Geologic Time Scale
The Geologic Time
Scale was
originally laid out
using relative
dating principles.
Absolute Dating
Absolute numerical dating takes
advantage of the "clocks in
rocks" - radioactive isotopes
("parents") that spontaneously
decay to form new isotopes
("daughters") while releasing
energy.
Radioactive
Isotope
An unstable atom that
will give off energy
and decay into another
type of atom.
Decay
Decay of the parent isotope Rb-87
(Rubidium) produces a stable
daughter isotope, Sr-87
(Strontium), while releasing a beta
particle (an electron from the
nucleus). ("87" is the atomic mass
number = protons + neutrons.
Rate of Decay
• Radioactive isotopes decay at constant rates
• The rates are different for each type of
isotope
• A graph of isotope decay over time is called
a decay curve
Decay Curve of U-238 to Pb-206
Using Decay to Calculate Age
Many minerals contain radioactive
isotopes. In theory, the age of any of
these minerals can be determined by:
• 1) counting the number of daughter
isotopes in the mineral, and
• 2) using the known decay rate to
calculate the length of time required to
produce that number of daughters.
Half-Life
The amount of time it takes for
50% of the parent radioactive
isotope to decay to its stable
daughter isotope
Isotopes trapped in rocks are
measured
How much U-235 is left after
2 billion years?
Carbon Dating
The radiocarbon dating method
has evolved into the most
powerful method of dating
fossils, artifacts and geologic
events up to about 50,000
years in age.
C-14 Dating
• N-14 in the
atmosphere is
converted to C-14 by
cosmic radiation
• C-14 enters food chain
through
photosynthesis
• C-14 decays back to
N-14
What is the half-life of C-14?
PotassiumArgon Dating
• In order to date older fossils, scientists must
use other radioactive isotopes. A commonly
used technique is called Potassium-Argon
dating. The element potassium is found in
most rock-forming minerals, and the half-life
of the radioactive isotope Potassium 40 is
1.25 billion years, allowing measurable
quantities of Argon 40 (its decay element,
known as the daughter element) to
accumulate in potassium-bearing minerals of
almost all ages.
Drawbacks of Absolute Dating
• Absolute Dating can only be performed in igneous
rocks, not sedimentary rocks
• Fossils older than 50,000 years cannot be dated,
their age must be estimated using the surrounding
rocks
• Most fossils are found in sedimentary rock layers
• Scientist then age the igneous rock layers above
and below the fossil to determine an age range
Ok then, what are fossils and how
do they form?
• Think about it? What actually is a fossil?
Do you know?
• How does it form?
• Write it down.
• Share with a neighbor
How Fossils Form
Permineralization: replacement of tissues with
minerals
Molds: sediments compact around tissues which
dissolve and leave cast of organism
Trace: organism leaves evidence of its presence
such as footprints
http://www.panzainteractive.com/projects/fossils/
Memories of the Past
Memories of the Past
Memories of the Past
Tar Pits
Tar Pits
Trapped in
Amber
Just like in
Jurassic Park
Trapped in Ice
A 6-to-12-month-old male Mammoth, nicknamed Dima,
found enclosed in a lens of ice six feet below the surface
in Siberia in 1977, with grass and sand still in its mouth.
Conclusion
• Living mammal distribution indicates
periods of isolation, selection, and
speciation
• Fossils of ancient organisms are found
everywhere, memories of earth’s rich
heritage
• Scientists can date the age of the rocks and
thus begin to reconstruct the history of life
on earth