Download 12-Mid-Late Ordovici..

Mid-Late Ordovicium: Ice age,
orogenic movements, life
colonizes land
Jarðsaga 1
-Saga Lífs og Lands –
Ólafur Ingólfsson
Plants colonize land towards the
end of the Ordovician Period
Barren Lands before the
colonization by plants
and animals...
490-450 MY ago, during the Ordovician, the land was still
desolate and empty. Barren, rocky grounds, empty sand
and gravel- plains. In rivermouths, where the water
regularly flooded the land, it was probably green with
algae. Deltas and tidal flats provide environment for life
to enter land from the sea...
First life on land
One of the most imortant
developments of the Ordovician was the colonization of
land. Microssils of cells and
spores of bryophyte-like
(bryophyte= mosi) early land
plants are known from this
time. The earliest terrestrial
arthropod (liðdýr) tracks are
also known from the
Ordovician.
Plants and green algae – common
ancestor – plants evolve from algae
Plants & the Colonization of Land
Plants first appeared on land towards the end of the
Ordovician Period. Liverwort-like (Bryophytes - mosar)
may have been first. Major step in plant development,
as terrestrial and aquatic environments are very
different.
Terrestrial Advantages.
z Greater access to CO2. Gases diffuse 10,000 x
faster in air than water. Photosynthesis much
faster. More CO2 probably the most crucial
advantage.
z More light. Water decreases light supply.
z Less mechanical damage (Air less dense).
z Initially no predators (herbivores). Plants
invaded land first.
Plants & the Colonization of Land
Terrestrial Disadvantages - quite a few!
z Desiccation. Plants/animals need constant
access to water. Perhaps the most crucial
disadvantage.
z Temperature of air fluctuates substantially
over daily and seasonal cicles . Water buffers
temperature changes.
z Plants encounter gravity - no buoyancy, because
air less dense than water.
z Too much light for shade plants, especially UV.
z Restricted access to water for sperm to swim
to egg.
z Not bathed in water and minerals, so must
“search” for them.
Plants & the Colonization of Land
Many new features needed to adapt higher plants
(and animals!) to terrestrial life:
z Multicellularity enables development of specialized
cells, tissues, and organs to reduce disadvantages.
z Epidermal (yfirborðs-) & cork cells, & cuticle (wax
layer) reduce water loss.
z Stomata (- loftauga - leaf pores) regulate gas
exchange to reduce water loss.
z Roots “mine” soil for water and minerals to
transport to the shoots.
z Vascular tissues (æðavefur) in roots, stems and
leaves transport water and minerals from root to
shoot.
PLANT
LEAF
performs
photosynthesis
CUTICLE (yfirborð)
reduces water
loss; STOMATA
allow gas exchange
STEM
supports plant
(and may perform
photosynthesis)
Surrounding water
supports the alga
ROOTS
anchor plant;
absorb water and
minerals from
the soil (aided
by mycorrhizal
fungi)
WHOLE ALGAE
performs
photosynthesis;
absorbs water,
CO2, and
minerals from
the water
HOLDFAST
anchors the alga
ALGAE
There seem to be many disadvantages to
life on land - the aquatic environment
seems much more attractive.
So why are the vast majority of
today’s plant species terrestrial?
– Plant colonization of land began ~ 475 MY
ago
– Animals followed plants on land ~75 MY
later, around 400 MY ago
Late Ordovician continental configuration
The drift of Gondwana towards the south
pole caused a continental glaciation towards
the end of the Ordovician...
The impacts of the Ordovician glaciation
The late Ordovician glaciation
was a global
phenomenon that
affected the
biosphere,
hydrosphere and
atmosphere. The
ice-sheet was
centred on West
Gondwana and
resulted in sealevel falls of ca.
50-100m.
An Ordovician esker in
Tunisia
Large glaciations
are one major
control on global
sea level
Sea level fluctuations
through time
Factors influencing sea level
in time and space:
1. Changes in the
Hydrological Cycle
2. Changes in the volume of
the Ocean basins
3. Tectonic and isostatic
movements
4. Thermal state of the
Oceans
5. Geoidal changes
Development of the Late Ordovician
ecosystem
• In the later part of the Ordovician, genera of
families previously limited to one faunal province
appear in another, indicating a tendency towards
migration and cosmopolitism.
Development of the Late Ordovician
ecosystem
• Changes in oceanic circulation (distribution
of planktonic larvae etc) along with
approaching continental masses would have
made possible migrations of shallow water
benthos.
•Among the losers of the Ordovician are
trilobites, which begin their decline in the
middle Ordovician, and stromatolites, whose
decline would seem to be due to pressure by
grazing herbivores (gastropods, echinoids,
etc).
Water depth history
Distribution of Ordovician species
in Mohawk Valley, New York
Species are not
found randomly, but
in groups. If species
reflect the environment, then the
abundance of the
species should be a
measure of the
environment. There
is a set of mathematical techniques
called "ordination
methods", which
attempt to do just
that. The gradients
could be many
things – salinity,
temperature, depth,
turbidity etc. Used
to reveal patterns
in time and space.
Some Late Ordovician fossils
Isotelus maximus
Prasopora bryozoa
Fossils from Winnepeg
Fossil Macroalgae : On the left, a fossil of Winnipegia cuneata, the
most common alga in the Lake Winnipeg flora. At center, Manitobia
patula, a putative member of the Floridean red algae, a group found
today in warm seas. On the right, Kinwowia articulata, a feathery
algae that may belong to the green algae.
Ordovician sedimentary rocks
Calcilutite, a rock composed of
calcareous mud deposited as
turbidite flows.
“Dinosaur Leather“, an Ordovician siltstone.
The surface carries "flute casts". These
form as a result of turbulent sedimentladen current scouring a muddy bottom.
Stromatolite reef
Ordovicium in Scandinavia
Ordovician slates and
limestone, Fornebu, Oslo
Ordovician fossils from Norway
Graptholith
Bryozoa
Asaphus sp.
Discoceras sp.
Brachyopod
The Taconic Orogeny
1. During Cambrian, Laurentia,
(North American Craton ) is
on it's way to a chain of
volcanic islands. NA is rotated
about 90o on its axis relative
to its present position.
2. The subducting NA plate, in
Ordovician time collides with the
island arc to form the Taconic
Orogeny. Several thrust sheets
are shoved westward. Avalonia,
another volcanic arc, is also on
its way.
Continents
in Late
Ordovician
The Taconic Orogeny took place about 450 million years
ago. As the two plates collided an extensive amount of
uplifting and fracturing occurred within the edges of the
continents which now make up the Taconic Mountains in
eastern New York. At the time of formation these
mountains were as high as the Himalayas but have since
undergone extensive erosion.
– a collision between N.
America and a volcanic
arc
– sequence of events
• subduction initiating to
the west, arc develops
• thrust loading from arc
warps shelf
– shales, turbites deposited
in the basin
• collision of arc produces
thrusting, mountain belts
• terrestrial clastics
prograde out over basin
– red oxidized shales and
sandstones
The Taconic
Orogeny
Cross section and rocks
Ordovician pillow lavas
Cambrian slates overriding
Ordovician limestone
A view of the Taconic Mts, SE-NY
Once like the Himalayas, now heavily eroded, reaching about 1100 m a.s.l.
The Ordovician mass
extinction
Mass extinctions of tropical marine faunas occurred
at the end of the Ordovician when 100 or more
families became extinct, including more than half of
the bryozoan and brachiopod species. 60% of all
marine invertebrate genera went extinct. One of the
greatest mass extinctions recorded in Earths history.
Causes of the mass extinction
Possible causes which have been suggested
include:
• climatic cooling in connection with the glaciation on Gondwana
• global sea level drop
• Tectonic plate movements closing the Iapetus
Ocean (proto-Atlantic), eliminating habitats
• The Taconic Orogeny
Even so, life in the Ordovician did not seem as precarious
as in the Cambrian (perhaps ecosystems being now more
complex), and enough Ordovician biota survived to radiate
to even greater diversity during the Silurian
Is there a pattern to mass
extinctions?
Detailed analysis of the number of different marine
organisms over time may suggest that there is a cycle of
extinctions, with an extinction occurring every 26-30 MY
Is there really a cycle?
The problem lies not only with an incomplete fossil
record, but also with problems of dating fossils
accurately enough to produce a reliable result. It may be
that the cyclicity is the result of poor information.
If there is a pattern to mass extinctions, it has
important implications: it suggests that there may be a
single cause for all the extinctions.
Why do some animals become extinct
and others not?
Graptolith
Eoblattus
When habitats disappear or
change drastically some species
will survive. We don't know what
determines 'winning' species.
Luck may play an important part
in deciding who makes it through
a mass extinction.
It helps to be an opportunist and
a generalist, able to survive in a
wide variety of conditions and to
quickly take advantage of any
favourable changes, and it helps
to be able to reproduce quickly.
A summary of major Early Paleozoic events
References, web resources etc
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Stanley, Earth System History, chapter 12
Fortey, R. Life – A natural History of the first four billion years of life on Earth.
New York, Vintage Books, 346 pp.
Fortey, R. Trilobate – Eywitness to Evolution. London, Flamingo, 246 pp.
http://www.ucmp.berkeley.edu/cambrian/camb.html
http://jan.ucc.nau.edu/~rcb7/global_history.html
http://www.gps.caltech.edu/~devans/iitpw/science.html
http://www.palaeos.com/Paleozoic/Cambrian/Cambrian.htm
http://www.palaeos.com/Paleozoic/Ordovician/Ordovician.htm
http://www.ic.sunysb.edu/Stu/ckramer/TaconicOrogeny.htm
http://www.peripatus.gen.nz/Books/WonLif.html
http://www.toyen.uio.no/palmus/galleri/blader/blad_x03.htm
http://www.fossilmuseum.net/Paleobiology/Paleozoic_paleobiology.htm#Ordovici
an
http://www.jamestown-ri.info/acadian.htm
http://greenfield.fortunecity.com/shell/89/
http://vulcan.wr.usgs.gov/LivingWith/
VolcanicPast/Notes/taconic_orogeny.html
http://www.ucmp.berkeley.edu/ordovician/
ordovician.html