what can we learn from fossils?
clues about the activites of ancient organisms
Radioactive dateing works best with what types of rocks?
why are index fossils useful to geologists?
they tell relative age of rock in which they occur
during the cambrian period of the paleozic era,what were the main life forms and where did they live?
invertebrates that lived in the sea
what is another name for the cenozoic era?
age of mammals
what do most scientist think caused the mass extinction of dinorsaurs at the end of cretaceous?
an object from space struck earth
what is a fossil?
the preserved remains or traces often an organism
what is the half-life of a radiactive element?
the time it takes for half of the radioactive atoms in a ssample of a radioactive element to decay\
when an intrusion of igneous rock is found intersecting sedimentary rock layers what does thi tell us?
the intrusion is younger than the rock in intersects
name the periods of the mesozoic era ?
triassic, jurassic , cretaceous ,
what is evolution?
the process by which all the different kinds of living things have changed over long periods of time
during which era do scientists believe that earth' atmosphere oceans and contients formed?
what is a petrified fossil?
a fossil formed when minerals replace all or part of an organism
how do most fossils form?
living things die and their remains are buried by sediments?
nmae for eras of geolagic time
precambrian, paleozoic, mesosoic ,cenozoic
how are geologists able to determine the absolute age of rocks?
what are index fossils?
fossils of organisms that are widely distributed but only lived during a shprt period of time
what is pangea?
a super contenient formed when earth continents move together
state the law of superposition
in horizontal layers of sedimentary rock, each layer is older than the layer above it and younger than the one below it
what does extinct mean?
organism no longer exists on earth
name the common organism that lived or lives during each of the eras of geologic time