Mid-Late Ordovicium: Ice age, orogenic movements, life

colonizes landJarðsaga 1

-Saga Lífs og Lands –

Ólafur Ingólfsson

Plants colonize land towards theend of the Ordovician Period

Barren Lands before thecolonization 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 imortantdevelopments of the Ordo-vician was the colonization of land. Microssils of cells andspores 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 LandPlants 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.Greater access to CO2. Gases diffuse 10,000 x

faster in air than water. Photosynthesis much faster. More CO2 probably the most crucial advantage.

More light. Water decreases light supply.Less mechanical damage (Air less dense).Initially no predators (herbivores). Plants

invaded land first.

Plants & the Colonization of Land

Terrestrial Disadvantages - quite a few!Desiccation. Plants/animals need constant

access to water. Perhaps the most crucial disadvantage.

Temperature of air fluctuates substantially over daily and seasonal cicles . Water buffers

temperature changes. Plants encounter gravity - no buoyancy, because

air less dense than water.Too much light for shade plants, especially UV. Restricted access to water for sperm to swim

to egg.Not bathed in water and minerals, so must

“search” for them.

Plants & the Colonization of LandMany new features needed to adapt higher plants (and animals!) to terrestrial life:

Multicellularity enables development of specialized cells, tissues, and organs to reduce disadvantages.

Epidermal (yfirborðs-) & cork cells, & cuticle (wax layer) reduce water loss.

Stomata (- loftauga - leaf pores) regulate gas exchange to reduce water loss.

Roots “mine” soil for water and minerals to transport to the shoots.

Vascular tissues (æðavefur) in roots, stems and leaves transport water and minerals from root to shoot.

PLANTLEAFperformsphotosynthesis

CUTICLE (yfirborð)reduces waterloss; STOMATAallow gas exchange

STEMsupports plant(and may performphotosynthesis)

Surrounding watersupports the alga

ALGAE

WHOLE ALGAEperformsphotosynthesis;absorbs water,CO2, andminerals fromthe water

HOLDFASTanchors the alga

ROOTSanchor plant;absorb water andminerals from the soil (aidedby mycorrhizalfungi)

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 southpole caused a continental glaciation towards

the end of the Ordovician...

The impacts of the Ordovician glaciation

The late Ordo-vician glaciationwas a globalphenomenon thataffected thebiosphere, hydrosphere andatmosphere. The ice-sheet was centred on West Gondwana and resulted in sea-level falls of ca. 50-100m.

An Ordovician esker in Tunisia

Large glaciationsare one major

control on global sea level

Factors influencing sea level in time and space:

1. Changes in theHydrological Cycle

2. Changes in the volume of the Ocean basins

3. Tectonic and isostatic movements

4. Thermal state of the Oceans

5. Geoidal changes

Sea level fluctuationsthrough time

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 (distributionof planktonic larvae etc) along withapproaching continental masses would have made possible migrations of shallow water benthos.

•Among the losers of the Ordovician aretrilobites, which begin their decline in themiddle Ordovician, and stromatolites, whose decline would seem to be due to pressure by grazing herbivores (gastropods, echinoids, etc).

Water depth history Species are not found randomly, butin groups. If speciesreflect the environ-ment, then theabundance of thespecies should be a measure of theenvironment. Thereis a set of mathe-matical 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.

Distribution of Ordovician speciesin Mohawk Valley, New York

Some Late Ordovician fossils

Isotelus maximus Prasopora bryozoa

Fossils from Winnepeg

Fossil Macroalgae : On the left, a fossil of Winnipegia cuneata, themost common alga in the Lake Winnipeg flora. At center, Manitobiapatula, 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

“Dinosaur Leather“, an Ordovician siltstone. The surface carries "flute casts". Theseform as a result of turbulent sediment-laden current scouring a muddy bottom.

Calcilutite, a rock composed of calcareous mud deposited as turbidite flows.

Stromatolite reef

Ordovicium in Scandinavia

Ordovician slates andlimestone, Fornebu, Oslo

Ordovician fossils from Norway

Graptholith Asaphus sp.

Discoceras sp.Bryozoa Brachyopod

The Taconic Orogeny1. During Cambrian, Laurentia, (North American Craton ) ison 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, inOrdovician time collides with theisland arc to form the TaconicOrogeny. Several thrust sheets are shoved westward. Avalonia, another volcanic arc, is also on its way.

Continentsin Late

Ordovician

The Taconic Orogeny took place about 450 million yearsago. As the two plates collided an extensive amount of uplifting and fracturing occurred within the edges of thecontinents 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.

The Taconic Orogeny

– 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

Cross section and rocks

Ordovician pillow lavas

Cambrian slates overridingOrdovician 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 occurredat the end of the Ordovician when 100 or morefamilies 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 extinctionPossible causes which have been suggested include: • climatic cooling in connection with the glaci-ation on Gondwana• global sea level drop• Tectonic plate movements closing the IapetusOcean (proto-Atlantic), eliminating habitats • The Taconic Orogeny

Even so, life in the Ordovician did not seem as precariousas 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 marineorganisms 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 hasimportant implications: it suggests that there may be a single cause for all the extinctions.

Why do some animals become extinct and others not?

When habitats disappear orchange drastically some specieswill survive. We don't know whatdetermines 'winning' species. Luck may play an important part in deciding who makes it through a mass extinction.

It helps to be an opportunist anda 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.

Graptolith

Eoblattus

A summary of major Early Paleozoic events

References, web resources etc• 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