Download Visualizing Earth Science

A BRIEF HISTORY OF LIFE
ON EARTH
Objectives
• Describe how Earth’s environment has changed over
the past 4 billion years.
• Identify the minimum requirements for life.
• Describe the difference between prokaryotic and
eukaryotic organisms.
• Define the theory of natural selection and how
evolution works.
• Describe several ways in which fossils form.
• Describe the dramatic change in Earth’s biota during
the Cambrian Period.
The EverChanging Earth
• Changes in the
atmosphere and
hydrosphere
–
–
–
–
–
Early atm. had no O2
Oldest bacteria: 3.5 by
Blue-green algae-2.5by,
Photosynthesis
Banded iron formation
2.5-1.8 by
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The Ever-Changing Earth
• Photosynthesis
– A chemical reaction
whereby plants use light
energy to induce carbon
dioxide to react with water,
producing carbohydrates
and oxygen
• Oxygen content increases
in the atmosphere
Banded iron formations
formed during the transition to
more oxygen rich atm.
Cyanobacteria (algae)
produced the oxygen initially.
They formed the first fossils,
which were mounds of
calcium carbonate
(stromatolites)
The Ever-Changing Earth
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Oxygen content in the atmosphere increased starting
around 200 my. The deposition of large amounts of
organic matter on shallow marine shelves due to plate
tectonics may have allowed this increase.
Early Life
• Archean and proterozoic
life
– Prokaryote
• A single celled organism with
no distinct nucleus… or, no
membrane separates its DNA
from the rest of the cell- all
bacteria are prokaryotes
Early Life
• Eukaryote
– An organism composed
of eukaryotic cells– Cells have a well defined
nucleus
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Evolution and the Fossil Record
• Evolution
– The theory that life on
earth has developed
gradually, from one or a
few simple organisms
to more complex
organisms
– Charles Darwin
• “On the Origin of
Species by Means of
Natural Selection”
Evolution and the Fossil Record
• Natural selection
– Individuals that are well adapted to their environment have a
survival advantage
– They then pass on their favorable characteristics to their
offspring
• Species
– A population of genetically and/or morphologically similar
individuals that can interbreed and produce fertile offspring
• How fossils form
– Fossil
• Remains of an organism from a
past age
• Embedded/ preserved in rock;
– Trace fossil
• Fossilized evidence of an
organism’s life processes
– Includes tracks, footprints,
and burrows
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Life in the Phanerozoic Eon
• The Paleozoic era
– Began 542 million years
ago with the Cambrian
period, a time of
incredible diversification
of life; known as the
Cambrian explosion
– Development of hard
skeletons allowed much
more widespread
preservation as fossils.
trilobite
Life in the Phanerozoic Eon
• From sea to land (any
organism)
– Must have structural
support
– Must have internal
aquatic environment
– Must be able to exchange
gases with air instead of
water
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• Plants (first to move from ocean to
land)
– Land plants evolved from algae
600 million years ago
– Vascular plants evolved in the
Silurian period (444-416 my);
stems and limbs
– Stomata (openings in leaves for
gas exchange)
– Earliest plants were seedless:
mosses and ferns
– Gymnosperm (415-359 my)
• A naked-seed plant
• Sexual reproduction
• Ginkos and conifers
• Requires spreading of pollen
for reproduction
Life in the Phanerozoic Eon
Fossil and modern ginko;
naked seed plant.
Flowering plants and trees;
much later; Cretaceous time
(145-65 my); angiospermsseed enclosed
Life in the Phanerozoic Eon
• Arthropods
– First creatures to make
the transition from sea
to land
– Small, light and covered
in a hard shell called
chitin
– Modern arthropods
include crabs, spiders,
centipedes and insects
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Life in the Phanerozoic Eon
• Fishes and amphibians
coelacanth
– Chordates
• Must have at least a primitive
version of a spinal cord
• First fish to venture onto land
may have been a member of
an obscure orderCrossopterygii
• First terrestrial chordates,
amphibians, have never
become fully independent of
aquatic environment
(originated in Devonian).
lungfish
Life in the Phanerozoic Eon
• The Mesozoic Era
– Angiosperm
• A flowering , or seed-enclosed,
plant
– Reptiles, birds and Mammals
• One branch of amphibians
evolved into reptiles, the first
fully terrestrial animal
– Amniotic eggs
• Dinosaurs and birds appeared in
the Jurassic period
– 96% of all species became
extinct at the end of the
Paleozoic (the great dying).
Archaeopteryx-early
bird.
Life in the Phanerozoic Eon
First mammals; cretaceous.
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Life in the Phanerozoic Eon
• Mass extinction
– A catastrophic episode in
which a large fraction of
living species become
extinct within a
geologically short time
– Most famous mass
extinction occurred 65
million years ago.
• An estimated 70% of all
species died out.
Life in the Phanerozoic Eon
• The Cenozoic Era
– The departure of the dinosaurs gave
mammals a chance to grow and
diversify
– Mammals also benefitted from
high oxygen levels in the
atmosphere, larger brain sizes
continued to evolve
– The human family evolved
• Australopithecus (walked upright)
3.9-3.0 my
• Homo Erectus 1.8 my-300,00 y
• Homo Neanderthalensis 230,00030,000
• Homo sapiens
Life in the Phanerozoic Eon
• Mass extinction
– A catastrophic episode in
which a large fraction of
living species become
extinct within a
geologically short time
– Most famous mass
extinction occurred 65
million years ago.
• An estimated 70% of all
species died out.
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Life in the Phanerozoic Eon
Life in the Phanerozoic Eon
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