History of Plant Life

Earth forms - 4.6 b.y. ago
First life on Earth - 3.6 to 3.8 b.y.
- single-celled bacteria
Photosynthesis evolves - 3.0 to 3.5 b.y.
- utilization of sunlight as energy source
- release of O₂ into oceans and atmosphere
Metazoans - multicellular organism - 1.8 b.y.??
- clear fossil evidence 900 m.y.
For the first 3.3 b.y., life on Earth was confined to the oceans

Ordovician Period (505-438 m.y.)

First plants move out of the ocean onto land
Required major evolutionary adaptations
1) tough outer layer to resist desiccation
2) internal fluid transport system
3) reproduction scheme based on airborne spores

Devonian Period (408-360 m.y)

First forests appear
Consists of club mosses and seed ferns

Mississippian Period (360-320 m.y.)

First conifers evolve - pine trees are conifers
Scaled trees evolve - trees with scale-like bark

Pennsylvanian Period (320-286 my)

Coal swamps are widespread

Jurassic Period (208-144 m.y.)

Age of Dinosaurs
Angiosperms evolve - flowering plants.

Miocene Epoch (24-5 m.y.)

Grass evolves during Mesozoic (299 - 65.5 m.y.)
Grasses diversify in Miocene
Grassland biomes develop:
Grass is difficult to digest
Resulted in major evolutionary adaptations in mammal's dental and jaw structure, digestive track and limb structure.

Plants Today

Non-biologic classification
1) Natural Vegetation - naturally occurring plants
2) Human-influenced Vegetation
- genetically engineered plants (this includes domestication, selective cross breeding, gene splicing)

Plants Today

Geographic classification: Plants are grouped according to physical structure, size and shape
Perennials
- woody tissue plants
- survive from year to year
- trees, shrubs and lianas
Annuals
- upper structure of plant only survives one year
Herbs
- low level plants
- grasses and flowering plants.
Mosses and Lichens
- algae and fungus

Plants and Environment

Certain plants are only found in certain environments
Two main factors controlling the type of vegetation
1)
2)
Other Factors:

Water Availability

Amount of water available to plants does not necessarily mean precipitation
Supplied by precipitation in many locations or groundwater
Plants have adapted to high and low levels of water availability

Temperature

Controls the rate at which physiological processes take place
- warm T = higher biologic activity
- cool T = lower biologic activity
Plants have adapted to high and low temp. levels
General rule (water dependent)
- warm T = more plant species
- cool T = fewer plant species

Freezing

Water in a cell will freeze
When the water freezes it expands
Freezing results in damage to cellular structure in plants that are not adapted to cold climates
Cold climate plants move the water out of the cells into the space between cells

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