Fossil record
• 1. Provides evidence about the history of
life on Earth
• 2. Includes information about structure of
organisms, what they ate, what ate them,
and what environment they lived in
• 3. Shows how species have changed
over time.
• 4. Provides incomplete information about the
history of life.
• 5. Over 99% of all species that have lived on
Earth have become extinct.
How Fossils Form
• Most fossils form in
sedimentary rock.
• Sedimentary rock forms when
rock breaks down into small
particles of sand, silt, and clay.
• Dead organisms are buried
by layers of sediment, which
forms new rock.
• The preserved remains may
be later discovered and
studied.
Relative dating (law of superposition)• Age of a fossil is determined by placement
in different layers. Older fossils found
beneath newer fossils.
• The law allows us to determine age of fossils in
relation to other fossils but can’t determine the
actual age of the fossil.
 What assumption do paleontologists make when they
use relative dating to estimate the ages of fossils?
• Half-life – the length of time
required for half of the radioactive
atoms in a sample to decay.
EXAMPLE:
•
Two Common Radioactive Isotopes:
•
Potassium-40 (half-life = 1.3 billion years)
•
Carbon-14 (half-life = 5730 years)
How long is the half life for carbon 14?
• Radioactive Dating- Use of half lives
to determine the age of a sample.
• Can assign absolute age of fossils.
• Scientist calculate the age of a fossil
based on the amount of remaining
radioactive isotopes it contains.
Example:
• Carbon-14 begins to decay when an
organism dies. Carbon 12 doesn’t
decay so scientist compare 14 to 12
the more 12 there is compared to 14
the older the sample is
Example: Graph – Radioactive Decay of Potassium-40
1. How many years does it take potassium 40 to reach its half
life?
2. Why does the curve fall steeply and then start to level out?
3. What fraction of potassium 40 will be present after five halflives?
1.The fossil record consistently shows
evidence that
a.all forms of life have existed in all
geologic eras.
b.living organisms have only been on
Earth for a short time.
c.living things have changed over time.
d.ancient life-forms are much the same
as forms found living today.
2.Determining the age of a fossil
by comparing its placement
with fossils in other layers of
rock is called
a.carbon-14 dating.
b.fossil-indexing.
c.relative dating.
d.absolute dating.
1. What is the name of
the earliest era in
geologic time?
2. What are the periods
of the Paleozoic Era
from oldest to
youngest?
3. When did the
Cretaceous Period
end?
4. Which era and
period do we live in?
Formation of Earth
• Earth is thought to have formed about
4.6 billion years ago
• 3.5 billion years ago the first living
organisms appeared in the ocean
Endosymbiotic theory- Proposes that
eukaryotic cells arose from living
communities formed by prokaryotic
organisms.
Bacteria engulfed lots of
other bacteria became
organelles (chloroplast
and mitochondria) each
had their own DNA
became unicellular
Eukaryotic cells
overtime became complex
multicellular Eukaryotic
cells
Miller and Urey Experiment
Miller and Urey produced
amino acids, needed to
make proteins, by passing
sparks through a mixture
of hydrogen, methane,
ammonia, and water.
Suggests how simple
compounds found on early
Earth could have combined
to form the organic
compounds needed for life.
How cells formed
Miller and Urey Experiment
Energy from sun and
lightening triggered chemical
reactions to produce simple
organic compounds
Atmosphere contained
hydrogen, methane,
ammonium and water vapors
Simple organic compounds
link together to form small
proteins
The first life forms were
probably prokaryotes that
were anaerobic (no oxygen)
Passed sparks through
mixture of the below
chemicals
Used hydrogen, methane,
ammonia, and water
Made amino acids that
made proteins
Suggest how simple
compounds could have
combined to form organic
compounds needed for life