The Fossil Record-Issues

 Fossil record is not
complete!
factors to form
 Pretty good “general”  Radiometric Dating
information
 Use Carbon-14 for ages
 But there are “missing”
50,000 years or less
gaps
 Half-life is 5730 years
 Could be missing only
because they haven’t
been found yet
 Fossils take many
14Carbon
Question

 Suppose an organism has 20 grams of 14C at its time of
death. Approximately how much 14C remains after 11,400
years?
 Half-Life=5730 years
 1 half-life would take us to 10 grams (5,730 years)
 2 half-lifes would take us to 5 grams (11,460 years)
 ~5 grams
Rate of Speciation

 Current debate:
Does speciation happen gradually or rapidly? Or both?
 Gradualism
 Punctuated equilibrium
 Stasis
Gradualism

 Gradual divergence over
long spans of time
 assume that big changes
occur as the
accumulation of many
small ones
 Series of transitional
forms between ancestor
and current species
Gradualism Graph

Questions to consider

 What other process that we’ve previously discussed
would fit within the gradualism model for
evolutionary change?
 What about the fossil record? Can the incomplete
fossil record support gradualism for evolution?
 Would the evolution of humans be an example of
gradualism? Why or why not? (I think
that…because…)
Punctuated Equilibrium

 Rate of speciation is not
constant
 rapid bursts of change
 long periods of little or no
change
 species undergo rapid
change when they 1st bud
from parent population
 Not well-preserved in the
fossil record because of rapid
changes
 More info see:
http://evolution.berkeley.edu/e
vosite/evo101/VIIA1bPunctuate
d.shtml
Punctuated Equilibrium Graph

Punctuated EquilibriumQuestions

 What are some issues with punctuated equilibrium?
Stasis

 Situation when evolutionary lineages persist for long
periods without change.
 common but it has recently taken on a new importance
with the punctuated equilibrium debate.
So which theory is true?

 Both theories claim that they can explain the gaps in the fossil record.
The Gradualism theory states that the fossil record is incomplete and
that it is unlikely that all stages of evolution would be preserved let
alone found. However there have been a few species that show
Gradualism through the fossil record. Humans for example.
 Punctuated Equilibrium claims the gaps in the fossil record are not
just missing links but the actual process of evolution. They claim that
he evolution happens to rapidly to be found in a fossil record. As
shown before this has been proven countless times from T rexes to
shell fish.
 So in the aftermath what theory holds true?
 In the present it is still difficult to decide which statement is true
concerning the gaps in the fossil record since a limited number of fossils
have been collected and recorded. Research is ongoing today and possible
in the next few hundred years we may have an answer. But remember
these are both just theories and one or both could be proven wrong.