L8. Moving onto land Flashcards
What events were critical for the emergence of life on land?
- photosynthesis evolves
- great oxidation event
- ozone layer forms
- cambrian explosion
Ordovician
- before life on land
- mix of continents and shallow ocean shelves, rising and falling sea levels
- first true vertebrates (fish, with jaws) evolve from Pikaia
Barriers to move onto land
- UV radiation: water filters the light
- desiccation: aquatic organisms are adapted to being surrounded by water, needs systems that allow for the passage of water and gases in and out of the body
- gas exchange: gases and absorbed differently depending on whether they are in air or dissolved in water
- Buoyancy: water and pressure supports body tissues, air does not (land plants and animals need supporting structures)
- temperature fluctuations: sea temp has slow and little change
- mineral nutrition: water contains dissolved minerals for added nutrition (many aquatic animals are immobile)
- reproduction: aquatic organisms use water to facilitate reproduction
- vision and hearing: light and sound waves more differently through water compared to air
Why did life make the jump to the seemingly inhospitable land?
- exploit new niche
- escape predation
- First to colonize were algae that got energy from the sun. It was advantageous to grow near the surface, in shallow waters on coastal shelves
Evolution of green algae
- populations of green algae exposed to periods of drought in the intertidal
- overtime evolved from green algae to more complex forms that could survive entirely on land
- evolved into liverworts and mosses to then millions of year later into the plants we know
Plant adaptations to life on land
- desiccation: developed multiple cell layers and layer of surface wax, evolved roots or root-like structures that direct movement of water into the body
- gas exchange: roots, and stomata (pores that allow gas to enter)
- reproduction: spores/pollen that can survive desiccation, later adapted seeds
- buoyancy: evolved strong fibres and compounds that were structural strong (lignin and cellulose)
- temp flux: seasonal dormancy
- mineral nutrition: roots allowed plants to take minerals out of soil, symbiotic relationships with microbes in soil
Movement of animals onto land after plants
- animals moved onto land 30-100 Ma after plants
- this is because plants are at the bottom of the food chain so if animals went first there would be nothing to eat
First animals on land
arthropods (410-360 Ma)
- evidence: tracks in fossil record
- Not living on land but most likely just avoiding predation
- hard shell helped avoid UV rays and desiccation
- led to dramatic increase in diversity
Our ancestors moving onto land
Tikaalik (375 Ma)
- lobe-finned fish
- shared ancestor of all tetrapods
- transition fossil
- sturdy, jointed “arms” for terrestrial support
- still only coming to land for things other than permanent living
Emergence of our ancestors
Icthyostega (365 Ma)
- progressive evolution of limbs
- lived on land but still closely tied to water for reproduction
- didn’t quite go extinct, some lobe-fish species still exist
Why could so many groups colonize land?
- structures that evolved for other uses are also effective for living on land (exoskeleton, vertebrate skeleton, types of movement)
Animal adaptions for life on land
- desiccation: terrestrial animals have different adaptations (ex. waxy coating, scales, behavioural: living in damp habitats, only coming out at night)
- gas exchange: lungs and trachea
- reproduction: internal fertilization (no drying out, higher chance gametes will connect), eggs (can be on land, no drying out), viviparity: live birth (increased survival of offspring)
- buoyancy: exoskeleton of chitin, external shell, internal skeleton of cartilage and bone
- temp fluctuation: higher metabolism, high food requirement
- vision: sealed chamber of fluid
- hearing: fluid-filled ear (cochlea)
