I. The Record of Life on Earth
The organisms which inhabited
the Earth are sometimes preserved in the rock as fossils.
The study of fossils is
In addition, the presence of organisms can
be recorded through marks they leave in sediment as a result of their
Geologists call these
features trace fossils or ichnofossils.
The study of trace fossils is called ichnology.
A. What types of life exist (or have
We group organisms based
on their similarities into taxonomic groups or taxa.
There are six kingdoms of organisms:
- Animalia (animals)
- Plantae (plants)
- Monera (bacteria and blue-green algae)
- Fungi (mushrooms,
- Protoctista - formerly Protista
- Eubacteria (normal type environments bacteria and cyanobacteria)
- Archaebacteria (extreme type bacteria methane, sulfur
All organisms are composed of cells.
There is a fundamental difference between
organisms based on the type of cells:
- Cells with a nucleus (or nuclei) - Eukaryotic cells
- Cells without a nucleus - Prokaryotic
cells - Kingdom Archaebacteria and Eubacteria only. Even though these are generally
single celled organisms, recently there have been found to be predators
which are bacteria: Bdellovibrio
Revisions of this classification scheme
have been proposed, based on evolutionary relationships determined through the
study of molecular structures and sequences. In one revision recently proposed,
organisms would be grouped into three superkingdoms
- Bacteria (bacteria)
(sometimes called archaebacteria (perhaps
incorrectly) - as different from the bacteria as the eukaryotes are from
- Eucarya (animals, plants, fungi, and protists)
have been recently discovered, and live under extreme conditions (such
as in high temperatures, or in naturally acidic waters) where life was not
thought be able to exist. Such severe conditions are considered to be like
those encountered on the Earth during its earliest stages.
How do organisms get preserved as
Most fossils are the hard
parts of organisms:
Soft parts are rarely
- internal organs
To be preserved, an organism must be in an environment where it is
protected from oxidation and bacterial decay.
- Must be rapidly buried by sediment
- Must be shielded from oxygen (anaerobic or anoxic
Some rocks are made up almost entirely of
an accumulation of organic remains or shells or other hard parts of organisms
(coquina, fossiliferous limestone, chalk, diatomite,
C. In which environments are fossils most
Environments covered by water.
Particularly environments with a high sedimentation rate or
Examples: swamps, deep lakes, tar pits,
oxygen-minimum zone in the oceans.
What are the major animal groups?
Animals can be grouped
into the invertebrates (animals without backbones) and the vertebrates.
There are more than 20 invertebrate Phyla,
but the chief ones that are preserved as fossils include:
- Phylum Porifera - the sponges
- Phylum Cnidaria (formerly Coelenterata)
- the corals and jellyfish
- Phylum Bryozoa - the colonial moss animals
- Phylum Brachiopoda - the brachiopods or lamp shells
- Phylum Arthropoda - the insects, crabs, shrimp, lobsters,
trilobites and eurypterids
- Phylum Mollusca - the clams, snails, octopus, squid,
nautilus, and ammonites
- Phylum Echinodermata - the starfish, sand dollars, sea urchins,
crinoids, and blastoids
The vertebrates belong to Phylum Chordata (referring to the nerve chord that extends
down the center of the spine).
What can these fossils tell us about the
The study of the
interaction of ancient organisms with their environment is called paleoecology. In large part, paleoecology
depends on comparisons of ancient organisms with living organisms. We use modern
analogs to help us interpret something about the way in which the fossils
lived and related to their environment.
Fundamental concepts of ecology and paleoecology: Ecosystem - the organisms and their
environment - the entire system of physical, chemical, and biological factors
Habitat - the environment in which the organism lives
Community - the association of several species of organisms
in a particular habitat (the living part of the ecosystem)
Niche - the way in which the organism lives - its role or lifestyle.
Where do organisms live?
Each species has
particular environmental requirements that can be described in terms of
limiting factors such as:
- amount of light
- amount of water needed, or water depth
- water chemistry (salinity, pH, amount of dissolved oxygen, etc.)
- water energy or turbulence
- type of substrate (sand, mud, rock)
- amount of living space)
- amount of food required
- presence of predators
Some organisms live on the land, and some
live in the water.
- Land-dwellers are called terrestrial organisms
- Water-dwellers are called aquatic organisms
- Marine (inhabit saline sea water) - salinity of sea water is about 34
- 36 parts per thousand total dissolved solids, or about 3.5% salt.
- Non-marine (inhabit freshwater) - salinity of freshwater is about 1 part
per thousand total dissolved solids, or about 0.1% salt. Includes rivers,
freshwater lakes, springs, caves, wells, groundwater.
- Brackish (inhabit water of intermediate salinity) - brackish water is a mixture
of fresh water and sea water, and may be found in bays, deltas, lagoons,
estuaries, harbors, etc.
- Hypersaline - water of very high salinity, such as the
Great Salt Lake, Dead Sea, and some
tropical bays and lagoons with high evaporation rates.
Marine organisms inhabit
the pelagic realm - all of the water overlying the ocean floor. It can
be divided into:
- neritic zone
- overlying the continental shelves - from the low tide line to
approximately 200 m deep (600 ft)
- oceanic zone - the
deep ocean seaward of the continental shelves, which can be divided into:
Near the shore, organisms inhabit the littoral environment
(the shoreline or tidal zone)
- bathyal zone (200 - 4000 m deep)
- abyssal zone (4000 - 6000 m
- hadal zone (more than 6000 m deep) - the extreme
depths found in the deep sea trenches. Note that the deepest point in the
oceans is in the Mariana Trench, 11,033 m deep.
Terrestrial organisms may inhabit one of
the following environments:
- Lacustrine - lakes and ponds
- Fluvial - rivers and
- Paludal - swamps
- Eolian (or aeolian) -
Modes of life
Mode of life consist of:
Within the neritic zone,
animals may have varying modes of life:
- planktonic - small plants and animals that float, drift,
or swim weakly
- phytoplankton - plants and plant-like plankton, such as
diatoms and coccolithophores
- zooplankton - animals and animal-like plankton, such as foraminifera and radiolaria
- nektonic - swimming
animals that live within the water column
- benthonic or benthic
- bottom dwellers, whch may be either:
- infaunal -
living beneath the sediment surface
- epifaunal - living on top of the sediment surface
Bottom dwellers capable of
movement are called vagile or vagrant.
Bottom dwellers which do not move are called sessile.
Methods of obtaining
- Primary Producers or
autotrophs - produce their own food
through photosynthesis, and supply food and energy for other
- Consumers or heterotrophs - cannot produce their own food
and must eat.
Predation - one species eating another.
- Herbivores - heterotrophs that eat plants
- Carnivores - heterotrophs that eat herbivores
and other carnivores
- Other feeding modes which may fit into the
- Parasites - derive nutrition from other organisms without killing them
- Scavengers - derive nutrition from dead organisms
- Suspension feeders - filter small food particles from the
- Deposit feeders or detritus feeders - ingest
sediment and extract small food particles
- Grazers - scrape food from the substrate
- Decomposers and Transformers - bacteria which
break down organic matter converting it into a form which can be
utilized by other organisms (nutrients)
The food chain or