Fossils
What are fossils
Preserved remains or traces of ancient organisms that lived in the past/
According to the law of superpostion which layer of rock is the oldest?
the bottom
The time it takes for half of the radioactive atoms in a sample of a radioactive element to decay is the element’s
Half life
Potassium-40 is useful for dating very old rocks because it has a(n) ____________________of 1.3 billion years.
half life
Fossils usually occur in __________ rock.
sedimentary
The law of ___________ helps geologists determine the absolute age of a rock layer.
superposition
Earth’s earliest atmosphere lacked which gas that is necessary for life as we know it to exist today?
oxygen
Sometimes layers of rock are overturned so much that the _____________ rock layer may appear on the bottom, which is the reverse of what is ordinarily expected.
youngest
Footprints and trails are examples of _________ fossils.
trace
What is relative age?
the age of a rock compared to the ages of others.
Geologists divide Earth’s long history into smaller units that make up the_____________
geologic time scale
A(n) ____________________ is a gap in the geologic record where some rock layers have been lost because of erosion.
unconformity
A(n) ____________________ fossil forms when dissolved minerals replace the remains of an organism and then harden to form rock.
petrified
Geologists use radioactive dating to
determine the absolute ages of rocks.
Velociraptors lived during the ____________ era.
Mesozoic
What has the study of fossils allowed scientists to do?
Describe past environments and the history of life