AS Fossils and Time Flashcards
Fossil
used to describe any trace of past life. Fossils may be parts of organisms, such as teeth or shells or whole organisms such as body fossils. Fossils may also be traces of organisms, such as footprints and burrows.
Organism
an individual life form, such as an animal, plant, fungus or bacteria. Organisms may be a single cell or multicellular (many cells). Organisms may be preserved as fossils.
Body fossil
the hard parts of an organism, such as the skeleton or shell.
Replacement
atom by atom substitution of one mineral for another.
Dissolution
the process whereby minerals that make up the fossils are dissolved away and removed in solution by groundwater.
Taphonomy
the study of the process of fossilisation from the death of the organism to discovery of the fossil. It is an overlap area between biology and sedimentary geology.
Mould
the impression of the outside or inside of a fossil.
Cast
an in-filled fossil void, usually with another mineral.
Extant
organisms that are still alive today.
Extinct
organisms that are no longer alive today.
Death assemblage
a collection of organisms found in a different place and position than they occupied in life, such as a collection of disarticulated shells.
Disarticulated
organisms found as fragments, such as separate shells or parts of trilobites.
Life assemblage
a collection of organisms found within sediments in the same position as they would have been when they were alive, such as a bivalve in a burrow.
Geopetal structures
allow us to see the way up of a rock, for example a coral or bivalve in life position.
Derived fossil
weathered out of one rock and re-deposited in another. Different fossils may give conflicting dates.
Ornament
expressed on the surface of the fossil, such as ribs, tubercles, spines and growth lines.
Robustness
the ability of the fossil to resist abrasion. Robust forms are more likely to be preserved whole or with slight damage only.
Articulated
organisms found whole or connected, as in life.
Littoral zone
the high-energy area between high and low tide.
Anoxic
or anaerobic conditions lack oxygen and are unsuitable for life.
Trace fossils
formed by benthonic infaunal and benthonic epifaunal organisms. These can be aquatic or terrestrial, although the preservation potential for terrestrial traces is poor.
Tracks
footprints of an organism made when it moved along the sediment.
Trails
impressions of animals which were travelling. This could have formed due to part or all of the animal dragging along the surface of the substrate, for example a trilobite tail.
Resting traces
a type of trail as the whole body of the animal had stopped moving (rests).
Terrestrial
refers to anything formed on land.
Bioturbation
refers to burrowing or working the sediment in a way that disrupts the bedding. This is caused by the activity of living organisms.
Substrate
the name given to the sediment or rock on the sea floor.
Catastrophism
the theory that changes in the Earth’s crust during geological history have resulted chiefly from sudden violent and unusual short-lived events.
Gradualism
assumes that change comes about gradually or that variation is gradual in nature. It is a model applied especially in evolution (Phyletic gradualism) where one species is transformed into another by slow changes.
Uniformitarianism
maintains that slow, incremental changes such as erosion, created all the Earth’s geological features. Uniformitarianism holds that the present is the key to the past: that the geological processes observable now were acting in the same way in the past.
Absolute dating
gives specific dates for rock units or events given in millions of years before (Ma).
Relative dating
putting units or events into sequential order, by saying one event is older or younger than another.
Half-life
the time taken for half the unstable parent atoms to decay and form stable daughter products.
Closure temperature
the temperature at which a system has cooled, so there is no diffusion of isotopes in or out of the system.
Closed system
when a mineral neither gains nor loses atoms. The higher the temperature, the more likely exchanges of atoms or ions will be.
Phanerozoic eon
the eon of ‘visible life’. The explosion of hard-shelled and thus species that could be fossilised due to the increase in oxygen levels.
Period
a unit of time, a division of an era, e.g. the Carboniferous.
Xenoliths
pieces of rock within an igneous rock which have not been derived from the original magma but have been introduced from elsewhere. These are usually from the surrounding country rock.
Lateral variation
means there are changes in thickness or lithology in beds laid down at the same time.
Marker horizon
shows a bed or bedding plane with a change of lithology easily distinguished which covers a wide geographical extent.
Varve deposits
alternating light and dark layers of sediment in glacial lakes, with each pair representing one year. The summer deposits will vary in thickness according to the amount of meltwater produced and can be correlated.
Diachronous beds
have the same lithology but vary in age along their extent.
Zone fossils
(index fossils) those with the ideal properties to delimit a biozone which is often named after the fossil.
Stratigraphic range
the time between the first and last appearance of the fossil.
Assemblage
the combination of different fossils identified in a rock unit.
Biozones
intervals of strata that are defined by their characteristic fossils.
Benthonic
Organism live on or in the sediment substrate of the sea floor
Infaunal
Organism lives in the sediment, usually in a burrow. Many will filter feed. An example is a bivalve clam.
Epifaunal
Organism lives on the sediment substrate. An example is a bivalve oyster.
Vagrant
Organism moves around on the sea floor and is usually a scavenger or a predator. An example is a regular echinoid.
Sessile
Organism does not move around on the sediment substrate. Some are attached to the sea floor, others lie on the sea floor. Most will filter feed, an example is a bivalve mussel.
Pelagic
Organism lives in the water column typically in surface waters.
Planktonic
Floats in the water column to wherever the the currents will take the organism. This type of organism is usually a filter feeder. An example is a graptolite.
Nektonic
Actively swims in the water column. Most are scavengers or predators. An example is an ammonite.
Law of Superposition
The law of superposition in geology states that in a sequence of layered rocks, the oldest layer is at the bottom and the youngest layer is at the top (in the absence of evidence to indicate otherwise)
Current Eon
Phanerozoic
Order of 12 geological time periods from the Cambrian to the present
Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian, Triassic, Jurassic, Cretaceous, Paleogene, Neogene, Quaternary
Derived fossil
a fossil redeposited in a sediment which is younger than the one in which it first occurred
Anthropocene
The name of the proposed current epoch in which humans have had a substantial impact on the planet, proposed to start from 1950 but rejected.
