Evidence from the Fossil Record

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Evidence from the Fossil Record
In this presentation you will

• explore and evaluate the evidence for evolution
  from the fossil record

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Introduction
The Earth is over 4.5 billion years old, and life
has existed on it for most of that time.
Evidence for ancient life on Earth comes mainly
from fossils.
Fossils are the preserved remains or traces of
animals, plants, and other organisms from the
remote past.
The total of all fossils, and their placement in
rock formations and sedimentary layers, is known
as the fossil record.
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Geological Time
This diagram shows the appearance of life on
Earth.
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Dating
Scientists work out the dates of rocks using two
main methods.
1. By looking at the layers of rock or rock
strata, they can work out fairly easily which
rocks are older and which are younger. This gives
a relative date.
2. By measuring the decay of radioactive elements
in the rocks, then the actual age of rocks can be
found.
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Dating
Some particular fossils are also restricted to a
particular age, so these can also be used to date
rocks.
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Fossilization
Fossilization is a very rare occurrence because
most parts of dead organisms tend to decompose
quickly.
In order for an organism to be fossilized, the
remains normally need to be covered by sediment
as soon as possible.
Fossilization tends to favor organisms with hard
body parts, organisms that were widespread, and
organisms that existed for a long time.
Although larger specimens are more often on
public display, fossilized microscopic remains
are far more abundant.
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Fossilization Types
Specimens may be preserved by the addition,
removal, or rearrangement of chemical parts over
millions of years.
Bones are often preserved in this way.
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Fossilization Types
Impressions, molds, or casts may be left by
organisms lying in sediment.
These might show the inside or the outside of the
specimen.
A shell buried in sandstone may be leached or
dissolved by groundwater, leaving a mold of the
shell in the surrounding stone.
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Fossilization Types
Organisms such as insects or small frogs can
become trapped in pine resin. The pine resin
hardens over time, becoming amber and preserving
the organism inside.
This process can preserve both soft and hard
parts of the organism.
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Fossilization Types
The activities of organisms can leave markings in
sediment, which form trace fossils.
These markings may be foot prints, or they may be
holes from burrowing organisms.
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The Fossil Record
Fossils are mainly found in sedimentary rock.
Sedimentary rock is formed by layers of silt or
mud on top of each other producing a series of
horizontal layers called strata.
The lowest strata contain the oldest rock and the
earliest fossils, while the highest strata
contain the youngest rock and more recent fossils.
It is possible to find out how a particular group
of organisms evolved by arranging its fossil
records in a chronological sequence.
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The Fossil Record
Studying the fossil record may provide good
evidence for the theory of common descent.
By studying the number and complexity of
different fossils at different levels, we can see
that older fossil-bearing rocks contain fewer
types of fossilized organisms, and they all have
a simpler structure.
Younger rocks contain a greater variety of
fossils, often with increasingly complex
structures.
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The Fossil Record
Organisms have changed significantly over time.
In rocks more than 1 billion years old, only
fossils of single-celled organisms are found.
In rocks that are about 550 million years old,
fossils of simple, multicellular animals are
found. At 500 million years ago, ancient fish
without jawbones surface. At 400 million years
ago, fish with jaws are found.
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The Fossil Record
Gradually, new animals appear Amphibians at 350
million years ago, reptiles at 300 million years
ago, mammals at 230 million years ago, and birds
at 150 million years ago.
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Evolution of the Bird
The fossil record may contain evidence of the
evolution of birds from small feathered dinosaurs.
Archaeopteryx was an organism that lived around
150 million years ago. It had some bird feathers
and wings. It also had some features similar to
dinosaurs.
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Evolution of the Bird
Fossils of feathered dinosaurs from the Gobi
Desert and China have also provided possible
evidence of a link between birds and the
dinosaurs.
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Evolution of the Horse
The horse has one of the most complete fossil
records, showing how it may have evolved from a
small dog-like creature into the modern horse.
The fossil evidence also shows how the hoof may
have developed from the five-digit limb, which is
common to all four limbed creatures.
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Evolution of the Horse
As with other evolutions, it is thought that the
horse did not evolve in a straight line there
were many branches, some of which led to the
zebras and wild donkeys.
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Evolution of the Whale
Whales are thought to have evolved from a small
hoofed carnivore.
Some details are still uncertain but fossils have
been uncovered that support the theory of
back-to-the-water evolution.
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Evolution of the Whale
These animals are not necessarily a direct
ancestor of the modern whale. They may be side
branches, but each whale fossil shares new
features with modern whales. In the fossil
record, we can see the gradual accumulation of
these adaptations in the fossils that led to
modern whales.
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Evolution of Humans
Humans and chimpanzees are thought to have shared
a common ancestor that lived about 7 million
years ago.
Over time, fossil evidence is believed to show
that our hominid ancestors evolved larger brains
and bipedal motion.
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Evolution of Humans
Evidence of stone tool making is found from 2-3
million years ago. At this time, a number of
different hominid species were living.
The modern form of humans (homo sapiens) appeared
around 200,000 years ago.
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Fossil Record
Within the fossil record, some groups suddenly
appear, and others seem to be unchanged over
millions of years.
Species are thought to evolve at different rates.
Sometimes they evolve rapidly, sometimes
gradually, and sometimes barely at all.
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Fossil Record
The climate and geography changes over time, so
organisms may die out or move to more habitable
areas.
The process of fossilization is very rare. Those
that do occur may also get buried under mountains
or oceans.
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Punctuated Equilibrium
One observation about how evolution seems to
occur is called punctuated equilibrium.
In this idea, evolutionary change happens fairly
quickly, separated by long periods of stasis.
Quickly in geological terms means 50,000 to
100,000 years!
The trigger for the evolutionary activity could
be a change in climate or environment or,
perhaps, in response to a new predator.
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Question 1
Which of the following is an example of fossil
evidence that points towards a common ancestor?
A) The extinction of the dinosaurs
B) The trend towards fewer and simpler life forms
the further back we look in the fossil record
C) The evolution of whales directly from fish
D) The trend towards more diverse and more
complex life forms the further back we look in
the fossil record
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Question 1
Which of the following is an example of fossil
evidence that points towards a common ancestor?
A) The extinction of the dinosaurs
B) The trend towards fewer and simpler life forms
the further back we look in the fossil record
C) The evolution of whales directly from fish
D) The trend towards more diverse and more
complex life forms the further back we look in
the fossil record
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Question 2
Which of the following statements could be an
explanation for the sudden appearance of an
organism in the fossil record?
A) Previously the organism had lived in an
environment where fossilization did not occur.
B) Previously the organism had lived in a
different geographical location.
C) The organism had undergone a fairly rapid
period of evolution over 100,000 years, due to
adapting to a changing climate. This only appears
to be sudden in the fossil record of millions of
years.
D) All of the above.
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Question 2
Which of the following statements could be an
explanation for the sudden appearance of an
organism in the fossil record?
A) Previously the organism had lived in an
environment where fossilization did not occur.
B) Previously the organism had lived in a
different geographical location.
C) The organism had undergone a fairly rapid
period of evolution over 100,000 years, due to
adapting to a changing climate. This only appears
to be sudden in the fossil record of millions of
years.
D) All of the above.
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Question 3
'Evidence from the fossil record, such as similar
bone structure and feathered dinosaurs, supports
the theory that birds may have evolved from a
species of dinosaurs.' Is this statement true or
false?
Answer True or False.
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Question 3
'Evidence from the fossil record, such as similar
bone structure and feathered dinosaurs, supports
the theory that birds may have evolved from a
species of dinosaurs.' Is this statement true or
false?
Answer True or False.
True
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Question 4
Which of the following statements describes the
concept of punctuated equilibrium in evolution?
A) Some fossil evidence shows slow gradual
evolution through the fossil record.
B) Some fossil evidence shows long periods of
stasis followed by rapid change in species.
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Question 4
Which of the following statements describes the
concept of punctuated equilibrium in evolution?
A) Some fossil evidence shows slow gradual
evolution through the fossil record.
B) Some fossil evidence shows long periods of
stasis followed by rapid change in species.
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Summary
In this presentation you have seen

• how fossil evidence could be used to support the
  theory of a common ancestor

• that the fossil record shows sudden appearance,
  stasis and gradual progression

• some of the possible reasons for these different
  evolution rates

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