Transcript EVOLUTION OF LIFE - Phoenix Central School District

HOW DID LIFE EVOLVE
AND WHY?
organism with visible nuclei:
any organism with one or more
cells that have visible nuclei
and organelles
simple organism without
nucleus: an organism whose
DNA is not contained within a
nucleus, e.g. a bacterium
Some
major
episodes
in the
history of
life.
1. The Earth was formed ~4.5 billion years ago
2. It took ~500 million years for the crust to solidify.
3. The oldest fossils of microorganisms
• 3.5 billion years old
• embedded in rocks in western Australia
Prokaryotes dominated from 3.5 to 2 billion years ago
• during this time, the first divergence of life occurred:
Bacteria and Archaeon (single-celled microorganisms with no cell nucleus
and no membrane-bound organelles within their cells)
Fossilized evidence of bacteria
 Stromatolites are fossilized bacterial
mats. Many fossils of prokaryotes are
found in layers that make up the
prokaryotic mats.
4. Oxygen began accumulating in the
atmosphere about 2.7 billion years ago.
Cyanobacteria are photosynthetic
prokaryotes that are still present today
 produced oxygen.
The salt crust is just like a greenhouse window!
Banded iron formations are evidence of the age of oxygenic
photosynthesis – approximately 2 BYA
5. The oldest eukaryotic fossils are ~2
billion years old.
Symbiotic community of prokaryotes
living within larger prokaryotes.
 Mitochondria and chloroplasts
6. The oldest fossils of multicellular
organisms are ~1.2 billion years old.
7. The oldest animal fossils are ~700
million years old.
Animal diversity exploded ~540
million years ago.
8. Plants, fungi, and animals began
colonizing land ~500 million years ago.
a. First plants transformed the landscape.
b. Then animals were able to take
advantage of new niches (specialized area
in which evolution optimizes certain
species—eg. predators, parasites.
 Mammals evolved 50 to 60 million
years ago.
The
Cambrian
radiation
of animals
B. The origin of life
1. First cells may have originated by chemical evolution
involving 4 steps:
a. Abiotic (Non-biological) synthesis of small organic
molecules (monomers)  C + H = organic molecule
b. Monomers joined together to form polymers (proteins,
nucleic acids)
c. Origin of self-replicating molecules (inheritance of traits)
 proteins and polynucleic acids
d. Packaging of these organic molecules into protobionts. 
Aggregates of abiotically produced molecules that maintain
an internal chemical environment and exhibit some of the
properties associated with life (i.e. metabolism, growth).
2. Evidence that supports the four-stage hypothesis for the
origin of life
a. In the 1920s  Abiotic synthesis of organic molecules is
testable in the laboratory
Hypothesis: Conditions on primitive Earth favored chemical
reactions that synthesized organic compounds from inorganic
precursors. These conditions were different from what is now
present and include:
- Reducing environment (no oxygen, but instead H2O, CH4,
NH4, and H2) = lots of free electrons that could be used to
reduce carbon and produce organic molecules.
- Energy from lots of lightning, UV radiation (no O2 to block
UV rays from the sun) and volcanic activity (heat).
b. Miller and Urey in 1953
i. Tested the 1920’s Oparin-Haldane
hypothesis by creating conditions in which
there was:
- An atmosphere above warmed sea water
that contained H2O, H2, CH4, and NH3 and
- Electrodes that simulated lightning.
- From this setup, they obtained organic
compounds such as amino acids that were
collected in cooled water.
The MillerUrey
experiment
The experiment - organic molecules could be created out of
inorganic molecules!
So…….why don’t we see this happening in today’s world?
Any organic molecules that are now formed would be
used up by living organisms.
If microorganisms were created from these organic molecules
in the early Earth’s water bodies, this would have been an
example of spontaneous generation!
3. RNA was probably the first hereditary
material
Today, genetic information is usually
stored as DNA, but some organisms such
as viruses use RNA to store info.
4. The precursors of early life are known as Protobionts.
a. Protobionts form spontaneously in lab experiments from
mixtures of organic molecules.
b. They contain RNA that codes for metabolic proteins.
These protobionts absorb food and the proteins catalyze it
to make energy which can be used for growth and division
to daughter cells.
c. Natural selection would favor protobionts that grow and
replicate. When the organic molecules in the earth’s water
bodies were gone, the protobionts would “evolve” to either
obtain energy by photosynthesis or predation.
 It would only take the formation and evolution of one (1)
protobiont to give rise to the all the different organisms we
see today.
This 4.5 billion-year-old rock, labeled meteorite ALH84001, is believed to have
once been a part of Mars and to contain fossil evidence that primitive life may
have existed on Mars more than 3.6 billion years ago. The rock is a portion of a
meteorite that was dislodged from Mars by a huge impact about 16 million years
ago and that fell to Earth in Antarctica 13,000 years ago. The meteorite was found
in the Allan Hills ice field, Antarctica, by an annual expedition of the National
Science Foundation's Antarctic Meteorite Program in 1984. It is preserved at the
Johnson Space Center's Meteorite Processing Laboratory in Houston.
C. Major lineages of life
1. At first, two kingdoms were
recognized  Plants and Animals.
2. In 1969, Robert Whittaker developed
a five-kingdom system  Plants, Fungi,
Animals, Protists, and Prokaryotes
(Monera).
Whittaker’s
fivekingdom
system

Energy

Medium for growth
Geological Time Scale Diagram:
•
Precambrian Time (an Eon, since it is comprised of
three Eras) lasting from the formation of Earth
approximately 4.5 billion years ago until the first
abundant fossils appeared 545 million years ago.
• Paleozoic Era and its 7 periods -- 545-245 million
years ago when the primary Earth inhabitants were
fishes.
• Mesozoic Era and its 3 periods -- 245-66 million
years ago when the primary Earth inhabitants were
reptiles.
• Cenozoic Era and its two periods -- 66 million years
ago until present when the primary Earth
inhabitants are mammals.
Precambrian time
included almost all of
Earth's first 4BY. The
crust, atmosphere,
and the oceans were
formed, and the
simplest kinds of life
appeared.
Primordial Earth bombarded
The Mesozoic Era
was the Age of
Dinosaurs. Planteating dinosaurs,
such as this
Stegosaurus, fed on
cycads and conifers;
early trees that
thrived before
modern flowering
trees first appeared
Cambrian Explosion
invertebrates (animals without a backbone)
corals, mollusks (clams and snails)
and trilobites (flat-shelled sea animals
The Paleozoic Era
saw the development
of many kinds of
animals and plants in
the seas and on land.
The earliest land
plants appeared in
the Silurian Period,
about 440 million
years ago.
The Cenozoic Era
included the
Pleistocene Ice Age;
when glaciers swept
slowly across large
land areas before
melting. These great
masses of moving ice
created a variety of
landscapes in
northern lands.
Evolution is a change in the gene pool of a
population over time
Miller-Urey
Experiment
When the
primordial soup
(earliest organic
forms) were exposed
to energy, organic
compounds were
produced as shown
by this experiment.
Amino acids are small,
highly reactive molecules
composed of 20 to 30
HCNO atoms.
When amino acids link
together in strings they
form proteins.
Proteins govern chemical
reaction rates and form
the structural material for
cell parts, which lead to
complex life forms.
gases 
compounds 
proteins 
simple cells 
complex cells 
US!
The Primordial Soup Theory
(Out of the Slime)
The Primordial Soup Theory suggests that life began in a pond or ocean as a result
of the combination of chemicals from the atmosphere and some form of energy to
make amino acids, the building blocks of proteins, which would then evolve into all
the living species.
The Primordial Soup Theory states that life began in a warm pond/ocean from a
combination of chemicals that forms amino acids, which then made proteins
approximately 3.8 billion years ago.
The Russian Chemist A.I. Oparin and English Geneticist J.B.S. Haldane first
conceived this idea. Both developed their theory independent of each other in 1920.
In this theory, the basic building blocks of life came from simple molecules which
formed in the atmosphere (w/o oxygen). This was then energized by lightning and the
rain from the atmosphere created the "organic soup". The first organisms would have
been simple heterotrophs in order to survive by consuming other organisms for
energy before means of photosynthesis. They would become autotrophs by mutation.
Evidence now suggest the first organisms were autotrophs.
Chemist Stanley Miller and physicist Harold Urey did their famous experiment in 1950
to test this theory. They mixed gases thought to be present on the primitive earth at
that time: ammonia (NH3), water (H2O), hydrogen (H2); but no oxygen at that time.
A large number of complex chemical
reactions is the underlying process that
we call life.
The main ingredients for life are:
•energy source
• supply of nutrients (building blocks)
•self-regulating mechanisms
About 3.5 million years ago, our first
direct ancestor appeared,
Australopithecus africanus (best
fossil example), known as “Lucy”.
“Lucy” represented the first
physical evidence of a hominid.
Hominid: any of a family (Hominidae) of
upright bipedal primate mammals, which
includes recent humans, as well as extinct
ancestral and related forms and in some
recent classifications the gorilla,
chimpanzee, and orangutan.
[ homin- stem of Latin homo means "human being" ]
Kingdom:
Phylum:
Class:
Order:
Suborder:
Infraorder:
Parvorder:
Superfamily:
Scientific classification
Animalia
Chordata
Mammalia
Primates
Haplorrhini
Simiiformes
Catarrhini
Hominoidea
Family:
Hominidae
Genera
•Subfamily Ponginae
• Pongo – orangutans
•Subfamily Homininae
• Gorilla – gorillas
• Homo – humans
• Pan – chimpanzees
Primate: a member of an order of mammals with a large brain, and complex hands and feet;
including humans, apes, and monkeys.



Yo!
Around 13 million
years ago, a treedwelling primate
developed:
stereoscopic vision
high mobility
(upright stance)
opposable thumbs
As brains became
larger and more
refined, the shape
of the cranium
evolved.
The larger brain
allowed humans
to perform more
advanced tasks
which would
increase their
survival.