12-2) Fossils: EVIDENCE OF PAST LIFE Flashcards
what are fossils?
remains give proof of existence of animals of the past, can help solve mysteries of Earth’s past
What happens to dead organic material?
Scavengers could eat it or it decomposes and rots, bacteria and fungi digest it into organic compounds so it “disappears”
what are the two conditions to preserve an animal/plant to make a fossil?
- The body of the dead organism must be protected from the scavenger; quickly cover with sediment then buried.
- They have hard parts such as bones, shells, teeth, or plants with wood; less likely to be eaten/weathered away
what rock is fossil found in?
sedimentary rock
describe petrified remains
hard and rocklike fossils, most of original materials have been replaced by minerals, soft tissues decay quickly, dissolved quartz may flow through the spaces (tree trunks, tusks, dinosaurs)
describe molds
when seashells or other hard parts fall into soft mud or beach sand, covered by sediments, compaction and cementation turns sediments into rock, cracks let water and air reach the shell/hard part, then decays and leaves a mold
describe casts
when minerals then fill in the mold, hardening it into a rock, hardened material produces a cast
Weathering and erosion eventually expose fossil at surface
describe compression fossils or carbon films
two-dimensional organic remains;
as dead organisms are buried more sediments pile up creating pressure and heat, gases and liquids escape.
Thin film of carbon residue is left creating a silhouette of original plant
in swamps and deltas what forms?
large volumes of plant matter accumulate, coal forms.
Structure of original plant is lost when coal forms, used as a fuel not fossil
describe impression fossils
like compression fossils, two dimensional, does not contain organic matter but shows fine details of organism’s external structure
describe unaltered (original) remains
actual organism or parts of organisms are preserved with little change (insect in resin)
can be preserved in amber, frozen ground/mud, tar, etc
describe trace fossils
fossilized tracks or traces that animals leave behind, can tell size, behavior, diet, social life, etc
what is the fossil record?
all the fossils that geologists have found and arranged by their relative ages
what is fossil succession?
fossil organisms tend to be found in the same general order at different locations
what are index fossils?
fossils from a species that existed on Earth for short periods of time, widespread geographically, layers exposed
