How can we help?

You can also find more resources in our Help Center.

22 terms

Geological time

An ancient land mass that broke apart, beginning 160 m.y.a., to form continents as we find them today.
An era occurring between 570 - 230 m.y.a., characterized by the evolution of fish, insects, and reptiles. This era immediately followed the Precambrian era.
This is the oldest era. It lasted 4 billion years with very few fossils; contains the first 3 eons: Hadean, Archean, and Proterozoic
This era is best known as the age of the dinosaurs. It includes the Triassic, Jurassic and Cretaceous periods. It lasted from 251 to 65 m.y.a., marked by dinosaurs, gymnosperms and angiosperms, as well as the mass extinction at the end of the period.
This era started 65 m.y.a. and includes today. Land masses continue to separate. Known for the evolution of the first primates, the diversification of flowering plants, first humans, and the formation of the Himalayas.
Land bridge
A thin strip of land that connects two much larger land masses (continents) the Bering Strait was once a land bridge connecting Russia with Alaska.
A trace of an ancient organism that has been preserved in amber, ice, or sedimentary rock.
Originally sap from ancient trees, it has hardened to a solid semi-transparent material that sometimes captured an ancient insect.
relative dating
Method of determining the age of a fossil by comparing its placement with that of fossils in other layers of rock.
radiometric dating
A method for determining the absolute ages of fossils and rocks, based on the half-life of radioactive isotopes. C14 dating is probably the best known of this type of aging.
process that forms sedimentary rocks when all layers of sedimentary rock are compressed by the small layers above.
law of supposition
The youngest rock will be on top of older rock layers.
Carbon 14
The radioactive form of Carbon.
Changes in a species over time due to natural selection - those best fit for their environment will survive and reproduce more frequently than those not as fit (for that environment).
trace fossils
these fossils include molds, casts, petrification, burrows, and tracks of a once living organism
the process of replacing organic molecules with inorganic molecules leaving a type of trace fossil
unaltered fossils
these fossils are the actual once living organism (or part of it) trapped in ice, amber, or tar
The two conditions that are most likely to lead to fossilization.
(1) a hard skeleton or exoskeleton (2) a quick burial and/or lack of oxygen
Why would a jellyfish be unlikely to leave a fossil?
No skeleton or exoskeleton
The time it takes for half of the atoms in a radioactive element to break down from the radioactive 'parent' to the stable 'daughter' element.
Veins or fingers of igneous rock that shoot right through several layers of sedimentary rock disrupting the clear layers.
What is one of the best known elements in radiometric dating?