Transcript Geological Time Scale Scientific Theory of Earth and Life

Geological Time Scale
Scientific Theory of Earth and
Life’s History
Chapter 12 – sections 2 and 5
Geologic Time Scale
• Representation of the history of Earth
• Organizes Earth’s history by major
changes or events that have occurred,
using evidence from fossils and geology
(Earth’s crust)
• First established in 1800’s and early
1900’s; main divisions have stayed the
same
• Time scale is divided into units based on
the order in which different groups of rocks
and fossils were formed
• Estimated age of earth - formed 4.6 BYA
• Three Basic units of time are used:
Eras
Periods
Epochs
Page 367
See page 366
• Names of eras came from early ideas
about life forms seen as fossils
Paleozoic – “ancient life”
Mesozoic – “middle life”
Cenozoic – “recent life”
• Within the eras, boundaries are defined by
mass extinction events
• Adaptive radiation into the new niches
available determines new orgs seen
Galaxy perspective clip
How do we know age of fossils,
earth and environmental changes?
• Geological studies – rock patterns, tectonic plates,
volcanic activity, banding patterns on rock – chemistry
of atm.
• Radiometric dating – decay of radioactive elements
begins at death and has measurable rate over time
• Relative dating – fossil location – older = deeper –
index fossils
• Continental Drift – EX: Pangea
• Types of fossils lead to speculation of climate,
ecosystem
• Pangea video clip...you don’t need sound
here, just watch the first 2 minutes or so to
get a “moving” pic of the concept…
Pre-Cambrian Era: 3.5 BYA – 2 BYA
(about 7/8 of the Earth’s history!)
• Life evolves! – will cover the scientific
theories….in next set of guided notes….
• Prokaryotes show up – 3.5 BYA
ex. Stromatolites – fossilized bacteria (cyanobacteria)
• Simple Eukaryotes show up – 2.1 BYA
• Fossil problems? – no hard parts; limited
parts to preserve…
• Geological data provides info on
atmosphere
Banding Shows Oxygen Introduction
into Earth’s Atmosphere –
cyanobacteria (Precambrian Era)
Drawing of columnar stromatolites like the
ones shown in the picture above. Shows
internal layering and close-up of lamina
structure. Surface is covered by a felt of
cyanobacterial filaments that trap
sediment grains that are washed across
the mat surface. Abundant sediment
supply produces granular laminae, low
sediment supply produces layers rich in
organic matter (green in drawing).
Fossils of
stromatolites
•
This picture shows modern stromatolites (columns and mounds) in Shark
Bay (Western Australia). Although algal mats and films are common in
many modern sedimentary environments, they are rarely recognised
because of continual destruction (grazing) by snails, worms, and other
animals. Today, only in places where metazoan grazing is restricted due to
extreme conditions (high salinity, too hot, etc.; basically only cyanobacteria
can survive) can stromatolite domes like these form in ways that are
reminiscent of the Precambrian (when metazoan grazing was absent
because metazoans had not evolved yet). The Precambrian was the age
of microbes, macroscopically expressed in colonial structures that we call
stromatolites.
Paleozoic Era
Cambrian Period
• Life moved on to land during Paleozoic
Era
• Cambrian Explosion – diversification of life
occurred
• Segmentation developed in living things
(allowed for specialization of body parts)
• hard exterior parts developed –
exoskeleton
Paleozoic Era
Carboniferous Period
•
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•
•
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Atmosphere is 30% O2
Warm temps
Seed plants show up
Reptiles and amphibians
Giant insects!
Paleozoic Era
Permian Period
• Permian Extinction – 90% marine extinct;
70% land species extinct
• Toxic volcanic gases?
• New niches open = complex life – from
adaptive radiation again…
Mesozoic Era
Triassic – Jurassic -- Cretaceous
Periods
• Dinosaurs, fern-like plants, and mammals
show up in Triassic
• First trees, birds show up during Jurassic
• In Cretaceous, Dinosaurs diversify then go
extinct and Flowering Plants show up
Cretaceous/Tertiary Extinction
• KT Extinction – 65 MYA?
• Asteroid strikes Earth -- Causes major
Climate change due to ash and debris
released into atmosphere
• Crater off of Yucatan Peninsula could be
where…
• The Chicxulub crater -- a prehistoric
impact crater buried underneath the
Yucatán Peninsula in Mexico
• Its center is located near the town of
Chicxulub,
• The crater is more than 180 kilometres
110 mi wide and 12 mi in depth, making
the feature one of the largest confirmed
impact structures on Earth
• Asteroid that formed the crater was at
least 6 mi in diameter.
Greatest discoveries -- KT
asteroid theory
Cenozoic Era
66MYA - present
• Age of mammals
• Tertiary & Quaternary Periods
• Earliest ancestors of modern humans
appear near end of Tertiary period
• Homo sapiens appeared ~100,000 years
ago
Quaternary period
• 1.8 mya – present
• includes all modern forms of life
Ice Ages?
• Occurred throughout most Eras
• Most recent one ~20,000 years ago
• Cause – solar output? asteroid strike?
position of earth?
What forms basis of Geological
Time Scale?
• Earth’s environment has changed drastically over
time
• ESTIMATED 99.9% OF ALL ONCE LIVING
THINGS ARE EXTINCT!
• Organisms that are best “fit” (adapted) will survive;
those that aren’t  extinct
• Mutations bring more variation in phenotypes
which may or may not be better fit for environment
• Due to environmental changes and struggle for
existence, orgs may become extinct
• We are currently experiencing the LARGEST
MASS EXTINCTION IN HISTORY!
How do we know what ancestry?
• Comparative Morphology – homologous
structures
– Transitional Fossils
• Biochemistry – DNA/RNA; amino acids
• Comparative Embryology – similar
developmental phases –
– ALL vertebrates – post anal tail, gill slits, notochord!
Fossil Snake “Pelvis” with “Legs”
Snake ancestor?
• We will continue to look at these pieces of
evidence as we go in to the next
chapter….