The Transition to Land: Terrestrialization

The Terrestrialization Process:

TRANSITION TO THE TERRESTRIAL FLORA

	Phase I: Precambrian-Lower Ordovician	Phase II: Mid Ordovician-Lower Devonian	Phase III: Late Devonian -Recent
soil type	regolith: cryptolithic: microbial soils	bryophytic "polsterland"	true soils
plant type	cyanobacteria>>chlorophyta	Nematophytes, streptophytes	embryophytes
Carbon abundance
pCO2	8 to 16 times today (PAL)	gradual decline to PAL	.03 %

Differences between the aquatic and terrestrial environments: the properties of water

Physical factors

• Water has a high specific heat and this provides a thermal buffer for the aquatic organism
• Water absorbs UV radiation
• (Bouyancy) water profides physical support

Biological Factors

• The aquatic medium provides a supply of nutrient
• Dissolved gasses: water is required for gas exchange

Plant and animal adaptation to the terrestrial environment

cuticles: waxy substances are used to cover plant and invertebrate tissues, they help to seal in water and retard dessication

tracheids: plants combine a new substance, lignin, with cellulose to produce tracheids. These specialized cells provide structural support and conduct water through the interion portions of the plant body

gas exchange: animals develop various forms of lungs, plants develop stomata which regulate gas and water exchange with the surrounding atmosphere

spores: the inert organic compound, sporopollenin, is used to coat spores, producing an effective structure for dispersal and preservation over periods of low water or nutrient

The Establishment of Terrestrial Ecosystems

A simple diagram of the terrestrial carbon cycle. Carbon flow is in red, green links show gas exchange. Not all links are shown to completion. 1° producers are plants and algae, consumers generally referrs to animals and degraders include both fungi and bacteria.

Web Resources

• A quick look at the conquest of land from a botany course in Barbados.

   

most recent update: September 2, 1999