Transcript History of Life on Earth (Wk2 lecture)

Biol406, The Origin and History
of Life on Earth
Paloma Valverde
Outline
• How life originated on Earth?
• How life diversity evolved?
• What is the evidence?
– Geologic time scale/Fossils
• How can we tell how old a fossil is?
Kingdoms
Domains
Life Diversity and Classification
Multicellular organisms that have eukaryotic cells with
cell walls of cellulose and obtain energy by photosynthesis
Multicellular organisms that have eukaryotic cells with
cell walls of chitin and can not do photosynthesis
Multicellular organisms that have eukaryotic cells that
do not have cell walls and cannot do photosynthesis
Unicellular or multicellular with eukaryotic cells and very diverse
(some can do photosynthesis, some can not, move by different
mechanisms)
Unicellular, Prokaryotic, cell wall lacks
peptidoglycan, antibiotics do not inhibit their growth
Unicellular, Prokaryotic, cell wall has peptidoglycan,
antibiotics streptomycin and chloramphenicol
inhibit their growth
Domains:
Bacteria and
Archaea
A eukaryotic cell has
membrane-enclosed
organelles, the largest of
which is usually the
nucleus
By comparison, a prokaryotic
cell is simpler and usually
smaller, and does not
contain a nucleus or other
membrane-enclosed
organelles
Bacteria and Archaea are
prokaryotic
Plants, animals, fungi, and
protists are eukaryotic
Domain:
Eukarya
How Life Origin
oOriginated
on Early Earth?
of Earth
The "big bang" that produced the universe is thought to have
occurred 10 to 20 billion years ago.
The Earth formed as a hot mass of molten rock about 4.5-4.6
billion years ago (BYA).
Rubble from the forming solar system slammed the Earth about
4.6 BYA, keeping the surface very hot. As the bombardment
slowed down, temperatures dropped.
As it cooled down, chemically-rich oceans were formed from water
condensation.
It is thought that the early atmosphere had CO2, N2, H2O (vapor)
and H2 (but not oxygen, because initial organisms could not do
photosynthesis).
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Geologic time scale (I)
– The fossil record allows us to trace the history of
life, which has evolved during the Precambrian
time, the Paleozoic era, the Mesozoic era, and the
Cenozoic era.
– The first fossils are of prokaryotes dated about 3.5
BYA (billion years ago).
– Prokaryotes diversified for about 1.5 billion years
before the eukaryotic cell, followed by
multicellular forms, evolved during the
Precambrian time.
Geological time scale (II)
– The Paleozoic includes the Cambrian period, when
ancestors of all animals appeared, and the
Carboniferous period, when swamp forests on
land contained seedless vascular plants, insects,
and amphibians.
– The Mesozoic era is best known for dinosaurs,
cycads, and the origins of mammals and birds.
– The Cenozoic era is known for the development of
modern flowering plants and an adaptive
radiation of mammals (species of mammals
increased because dinosaurs went extinct).
Precambrian Times
MYA
• The Precambrian includes about 87% of the geologic
timescale
– Little or no atmospheric oxygen in the early atmosphere (4.5 BYA)
– Lack of ozone shield allowed UV radiation to bombard Earth
• The first cells came into existence in aquatic environments
– Prokaryotes (3.5 BYA)
– Photosynthetic cyanobacteria added oxygen to the atmosphere
(2.7 BYA)
– First eukaryotic cells (2.1 BYA) and Protists diversify (1 BYA)
– First multicellular organisms (soft-bodied invert, 0.6 BYA)
How did the first cell evolved on
the Earth?
• Several hypotheses suggest
– Organic molecules came from outer
space on comets and meteorites (Lack
of O2+ lots of radiation=new primitive
cell)
– Bacterium-like cells could have been
carried to Earth on a meteorite or comet.
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Origin of the First Cell(s): Protocell
Nowadays we
know that “life
only comes from
life (cells only
come from cells).”
Biological Evolution
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
cell
DNA
RNA
origin of
genetic code
protocell
plasma
membrane
polymers
polymerization
small organic molecules
Chemical Evolution
However, the first
cells on Early
Earth had to arise
from nonliving
chemicals.
energy
capture
abiotic
synthesis
inorganic chemicals
outgassing
from
volcanoes
early Earth
Origin of Prokaryotes
Prokaryotes might have evolved from the functional
assembly of monomers to form large organic molecules
RNA may have been first genetic material and selfreplicate (ribozymes)
Amino acids polymerized into proteins
Lipid bubbles with high concentration of organic
molecules became living protocells with cell membranes
First cells emerged between 3.5 BYA (ocean temperatures
are thought to be around 120-190 oF)
Prokaryotes ruled the Earth for at least one billion years (did
not have nuclear membranes and were very small).
How did Eukaryotic Cells Arise?
• Eukaryotic cells arose around 2.1 BYA.
• Explained by the Endosymbiotic Theory:
http://highered.mcgrawhill.com/sites/9834092339/student_view0/chapter4/
animation_-_endosymbiosis.html
• Mitochondria were probably once free-living aerobic
prokaryotes.
• Chloroplasts were probably once free-living
photosynthetic prokaryotes.
• A nucleated cell probably engulfed these prokaryotes
that became various organelles.
• Cilia and flagella may have originated from slender
undulating prokaryotes that attached to the host cell.
Protists diversify and Multicellularity/Soft
Invertebrates are formed
– About 1.4-1.5 BYA protists diversify
– First multicellular organisms arise (around 0.6
BYA), lacked internal organs and could have
absorbed nutrients from the sea.
– It’s possible that they practiced sexual
reproduction
During the Precambrian time, the first cell or cells (1) give rise to bacteria (2) and
archaea (3); the first eukaryotic cell evolves from archaea. Heterotrophic protists
(5) arise when eukaryotic cells gain mitochondria by engulfing aerobic bacteria,
and photosynthetic protists (6) arise when these cells gain chloroplasts by
engulfing photosynthetic bacteria. Animals (and fungi) (7) evolve from heterotrophic
protists, and plants (8) evolve from photosynthetic protists. BYA = billion years
Paleozoic and Precambrian Eras
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The Paleozoic Era
• Begins with the Cambrian Period
• Lasted over 300 million years
• The abundance of fossils of animals of the
Cambrian period may be due to the evolution of
outer skeletons, bones and teeth
• The ancestry of all modern animals can be traced
to the Cambrian period
• Includes three major mass extinction events
The Invasion of Land
• Plants
– Seedless vascular plants date back to the Silurian period
– Later flourished in Carboniferous period
• Invertebrates
– Arthropods were the first animals on land
– Outer skeleton and jointed appendages pre-adapted them
to live on land
• Vertebrates
– Fishes first appeared in the Ordovician period
– Amphibians first appeared in the Devonian period and
diversified during the Carboniferous period
• A mass extinction occurred at the end of the Permian
period
Cenozoic and Mesozoic Eras
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The Mesozoic Era
• Triassic Period
– Nonflowering seed plants became dominant
(Gymnosperms)
• Jurassic Period
– Dinosaurs achieved enormous size
– Mammals remained small and insignificant
• Cretaceous Period
– Dinosaurs declined at the end of the Cretaceous period
due to a mass extinction
– Mammals:
• Began an adaptive radiation
• Moved into habitats left vacated by dinosaurs
The Cenozoic Era (65 MYA-up to
now)
• Mammals continued adaptive radiation
• Flowering plants were already diverse and
plentiful
• Primate evolution began
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Fossils are the Evidence of Past Life
Fossils are the remains, imprints, or traces of
organisms that were once alive. By studying fossils,
paleontologists can learn where, when, and how those
organisms lived.
When an organism perishes, normally its soft parts are
eaten by scavengers or decomposed by bacteria.
Two conditions can allow preservation as fossils:
1) When rapid burial by sediment happens (soft parts
are protected from the environment)
2) When they have hard parts (bones, shells, teeth)
How about soft animals, plants?
-Preservation in amber (insects)
-Impression or tracks in sediment
The first abundant fossil
evidence does not appear
in the geologic record
until the beginning of
the Cambrian period.
In the Precambrian simple
life forms such as algae,
bacteria, fungi, and worms
predominated (without
hard parts)
Geologists and Paleontologists Determine
the History of Life on Earth
1) Dating of rocks by using radiometric dating of index
fossils
Index Fossils are from species that existed on Earth
for relatively short periods of time and were abundant
and widespread. Index fossils found in a sedimentary
rock layer can be used to help date the layer.
2) Law of superposition: This states that in undisturbed
layers of rock, the oldest rocks are on the bottom and the
youngest rocks are towards the top.
Radioactivity/Half-Life/Radiometric
Dating
Unstable radioactive isotopes: Nuclei of these elements
break apart/decay and emit radiation.
They are referred to as the parent, and the isotopes from
the decay of the parent are termed the daughter products.
The rates of decay are always the same.
Each radioactive isotope has a Half life: It is the time
required for half of the nuclei in the sample to decay.
Radiometric dating: If the half life of the radioactive isotope
Is known and the parent/daughter ratio can be determined,
the age of the sample can be calculated.
Half life of common isotopes
Example of radioactive decay curve
(exponential)