the remains, imprints, or traces of prehistoric organisms
where there is gap in the rock layers
Principle of uniformitarianism
Earth processes occurring today are similar to those that occurred in the past
the age of something in comparison to other things
Law of Superposition
in undisturbed rock layers, the oldest rocks are on the bottom and the youngest rocks are on the top
a type of fossil that indicates the geologic age of the rocks in which it is found
the amount oftime it takes for half of the atoms in an isotope to decay
the age, in years, of a rock or other object, such as a fossil
Age of Mammals
The Cenozoic Era is know as:
Age of Invertebrates
The Paleozoic Era is know as:
Age of Reptiles
The mesozoic Era is know as:
The plants characteristic of a geological period.
the animals characteristic of a geological period.
The seas covered the large areas of the continents two times during this era.
a space in a rock that has the shape of the remains of a living thing that once occupied that space.
a model in the shape of a living thing or its remains, it forms when minerals or rock particles fill the space
includes the footprints, tracks, trails, and burrows made by living things.
Atoms of the same element with different atomic masses
is a method using radioisotope carbon-14 to determine the age of objects such as fossils or rocks
the process in which organic material is changed into inorganic material such as a fossil
geologic time scale
the division of Earth history into blocks of time--eons, eras, periods, and epochs. The time scale was created using relative dating principles.
a geologic time unit; eons are divided into these, and inturn are divide into periods
Pre-Cambrian time covers from 4.6 billion to 544 million years ago. During this time life developed as bacteria and softbodied, multicelled organisms. First mass extinction probably occurred near the end of the Precambrian
the latest of the four eras into which geologic time is subdivided ; 65 million years ago to the present