Transcript document

The Early Stuff
Earth
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Based on radiometric dating of rock layers,
scientists agree that Earth is around 4.55
billion years old
The oldest rocks are 3.8 billion years old
During much of that time, only bacteria
inhabited the Earth
–
Eukaryotes have only developed in the past 1.8
billion years
Primitive Earth
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Due to the Sun's radiation, primitive Earth
was devoid of an atmosphere
The first atmosphere was formed by out
gassing of gases trapped in the interior of the
early Earth
Early Atmosphere
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The early atmosphere of Earth was a
reducing atmosphere and contained no free
oxygen
It consisted of gases released from volcanic
activity occurring underneath the surface of
Earth
As plants developed, the process of
photosynthesis resulted in the creation of
atmospheric oxygen
Photosynthetic Organisms
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Life started to have a major impact on the
environment once photosynthetic organisms
evolved
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These organisms, blue-green algae, fed off
atmospheric carbon dioxide and converted much
of it into marine sediments consisting of the shells
of sea creatures
As photosynthetic life reduced the carbon dioxide
in the atmosphere, they also started to produce
oxygen
Oxygen
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For a long time, the oxygen produced did not
build up in the atmosphere, since it was
taken up by rocks
The majority of oxygen produced over time is
locked up in the ancient rocks
It was not until about 1 billion years ago that
the reservoirs of oxidizable rock became
saturated and the free oxygen stayed in the
air
Ozone
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Once oxygen had been produced, ultraviolet
light split the molecules, producing the ozone
and UV shield as a by-product
Only at this point did life move out of the
oceans and respiration evolved
Today’s Atmosphere
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Today’s atmosphere is considered an
oxidizing atmosphere and contains nitrogen,
oxygen, carbon dioxide and water vapor
The Origin of Life
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There were two main ideas of how life came
about, biogenesis and abiogenesis
Biogenesis
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The process of life forms
producing other life forms
Living matter can only be
generated by other living
matter
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Abiogenesis
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AKA spontaneous
generation
Living organisms are
generated by decaying
organic substances
This belief was due to the
common observation that
maggots or mold appeared
to arise spontaneously
when organic matter was
left exposed
Francesco Redi
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An Italian physician who conducted an
experiment to try to disprove spontaneous
generation by observing maggots
He observed that these organisms appeared
on meat a few days after flies were present
and considered that instead of maggots
spontaneously arising, that instead it was
likely that flies lay eggs too small for people
to see
The Experiment
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Geologists have divided Earth’s 4.56 billion
year old history into units that represent
specific amounts of time
Eons represent the greatest expanses of time
Eons are then broken up into eras
Eras are divided into periods
Periods are split up into epochs
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There are 4 eons
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Hadean
Archean
Proterozoic
Phanerozoic
 This term is derived from the Greek “visible life”
 There are abundant fossils found here
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There are three eras in the Phanerozoic
◦ Paleozoic-ancient life
◦ Mesozoic-middle life
◦ Cenozoic-recent life
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This time frame takes up 4 billion years
before the start of the Cambrian period
It represents about 88% of the Earth’s history
but it is not divided into parts
There were few life forms which are difficult
to identify and rocks have been disturbed
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Each era is divided into periods
The periods of the Cenozoic are divided into
still smaller units called epochs
The epochs of the other periods are not
referred to by names instead by terms early,
middle and late
Evolution
Evolution
• The idea that organisms change over
time
• It is a theory that states that current
life forms have descended from
previous life forms through changes
in the structure and function of body
parts
Historical Ideas
• Until 1859, most biologists believed
in the fixity of species
– Two main scientists in this area were
J.B. Lamarck and E. Geoffroy SaintHilaire
• In 1859 the book On the Origin of
Species was published which
changed the beliefs of many
individuals
Lamarck and Hilaire
• Jean-Baptiste de
Lamarck
– Developed one of the
first (though incorrect)
theories of evolution
– He believed in what was
called the Inheritance
of Acquired
Characteristics
Theory
– He believed that
organisms changed
during their own life
spans to meet the needs
of their environment
• E. Geoffroy SaintHilaire
– He explained
adaptation by direct
effects of the
environment
– Lamarck rejected
this idea
Charles Darwin
• An Englishman born in
1809
• He explored parts of the
Galapagos Islands
(Western part of S.
America) by sailing on the
HMS Beagle
• He noted that there was a
lot of variety among the
same species of
organisms
– The two main animals he
focused his studies on were
finches and tortoises
• He wanted to find out if
there were patterns to the
ways animals reproduced
Darwin’s Voyage
• His voyage around the world convinced him
of several facts that could not be
explained:
– Different continents had different species
– Species sharing a land mass were often related
– Islands species were usually related to those of the
nearest continent
– Similar environments did not always produce the same
species or related species
• He published his findings in a book called On
the Origin of Species
• His studies became known as the Theory of
Evolution
• Darwin is known as the Father of evolution
On the Origin of Species
• In his book he was able to explain all
of his previous facts by a term called
Descent with modification
– A branching form of evolution very
different from earlier beliefs
• This book also suggested natural
selection as a mechanism for
evolutionary change
Ancestors
• The concept that animals change over
time and therefore look much different
than their ancestors is referred to as
descent with modification
• This idea implies that all living organisms
are related to one another which is called
common descent (meaning that all
species were derived from common
ancestors)
Darwin’s Finches
• Differences between similar species
suggests that animals came from a
common ancestor but developed
characteristics specific for their
needs
• Darwin observed in the Galapagos
Islands that finches developed
different bills that were specialized
for certain types of food
Natural Selection
• Very important aspect of evolution
• It occurs when members of a
community struggle for existence
(survival)
– This ability to survive is called fitness
• In this struggle, members must fight
for food, living space and other
necessities
• This struggle for existence is known
as “survival of the fittest”
Examples of Survival of the
Fittest
• Some animals can use camouflage to
hid from predators, the animals that
can hide best are going to be the
ones that are not seen (thus not
eaten!)
• Since these are the animals that can
survive, they will be passing that
trait on to their offspring
Variation
• Inherited variation happens when the
ancestors of one species have a mutation
that occurs in the gene to create new
members of the species; they are similar
in structure and form, but can vary
greatly, ex: dog breeds-labs and basset
hounds are both dogs but with obvious
differences
• Artificial variation/selection is when an
individual selects organisms based on the
physical characteristic and abilities of the
animal
Evidence of Evolution
Evidence
• Evidence is something
•
that helps form a
conclusion, in terms of
evolution, it comes from
several areas, the most
convincing is fossils
Fossils are traces of
previously living
organisms
– Include imprints of life
forms and bones
The Fossil Record
• Fossils become permanent through the
process of fossilization
• Fossilization begins as an organism is
buried in volcanic ash or in sediments
– As more sediments pile up on the burial site,
they exert more pressure on the remains and
over a long period of time, chemical changes
and pressure transform the organisms’
remains into fossil
Fossil Record
• Record of the fossils scientists have discovered
• We do not have a complete fossil record
• Scientists estimate they have fossils for about
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250,000 species even though there must have
been millions more in the past
Much of the fossil evidence has been lost to
use due to massive earthquakes and volcanic
eruptions
Relative Dating
• A technique used to determine the relative
age of a fossil
– Relative age is the age of one fossil compared
to the age of another
• Fossils in the same layer would be from
the same general time period
• The older the rock layer, the older the
fossils would be
Absolute Dating
• A way scientists can find the age of fossils
• They use this procedure to create a
timeline and have found that organisms
have become more complex over time
– Certain types of atoms decay over time
– One atom that scientists used to date fossils is
carbon-14
Carbon-14
• Carbon-14 is a radioactive form of carbon
and it is present in all living things
• The half-life (time it takes for ½ of the
atoms to decay) is about 5, 700 years
• As soon as an organism dies, C-14 starts
to decay
Carbon-14 Dating
Amount of C-14 Half-life
Years
10.000g
Start
0
5.000g
1
5,700
2.500g
2
11,400
1,250g
3
17,100
.625g
4
22,800
Species
Adaptations
• There are distinct species
that have adapted to
their environment by
changing their body
structure, ex: horses’ feet
– Early horses had four
toes
– Over a period of fifty
million years, horses
gradually made the
conversion to the
present one-toed animal
Homologous Structures
• Characteristics that have similar structures
but different functions are known as
homologous structures
• Similarities between living organisms
provide evidence that organisms seem to
have originated from a common ancestor
– Ex: a bird’s wing is similar to a human’s arm
both of which are similar to a whale’s flipper
Vestigial Organs
• Structures that appear homologous to
structures in other organisms, but appear
to serve no function
• Ex: human appendix and tailbone, these
structures no longer have any function in
the human body
– Appendices help digest food using small
pebbles and sand which comes from eating
from the ground