Fossils
Relative Age of Rocks
Geologic Time Scale
Early Earth
Eras of Earths History
100
What type of fossils provide evidence of the activities of ancient organisms?
trace fossils
100
the age of a rock compared to the ages of other rocks
relative age
100
according to scientists, both Earth and the moon are how old?
4.6 billion years old
100
Describe the earliest known forms of life on Earth
single-celled organisms
100
what organisms became abundant during the Silurian period?
plants became abundant & First insects on land
200
A solid copy of the shape of an organism 
a cast
200
a formation of igneous rock on Earth's surface is known as
an intrusion
200
________ _________ _________ is used by geologists to show Earth' history because the time span of Earth's past is so great
geologic time scale
200
according to scientists, Earth began as a ball of ____, _____, and _____
dust, rock and ice
200
single-celled organisms dominated which time period
pre-cambrian
300
how do most fossils form?
living things die and are buried by SEDIMENT that hardens into rock over time
300
in horizontal sedimetnary rock layers the oldest layer is at the bottom and the youngest layer is at the top.
law of superposition
300
geologists divided time between Precambrian Time and the present into three long units of time called ____
eras
300
during Earth formation, _________ is the force that pulled dust, rock and ice together to form Earth
gravity
300
the Triassic period, Jurassic Period, and Cretaceous Period occurred in the ________ era
mesozoic
400
name 2 substances that can preserve entire organisms
sticky tar, amber, ice
400
compare relative and absolute dating
relative dating puts organisms in time periods relative to one another (law of superposition states that layers nearer the surface are younger than layers deeper in the Earth).  Radioactive dating uses radioactive elements with known half-lives to determine the absolute age of an organism.
400
during the Triassic Period, _____________ appeared in the fossil record (warm-blooded vertebrates that feed milk to their young)
mammals
400
What are possible causes of mass extinctions on Earth?
a meteor hit earth, creating thick dust and clouds which blocked out the sunlight and prevented photosynthesis, killing food sources for living things up the food chain.


volcanic action created hazardous gases and dust that causes living things to die

400
Mesozoic era is often call the Age of ______ due to the success of these animals
Age of Reptiles
500
an extremely thin coating of carbon on rock
carbon film
500
the gradual change in living things over long periods
evolution
500
what is the name of the geologic period in which we are living?
quaternary period
500
what hypothesis explains why the Earth and moon are about the same age?
young Earth collided w/ a large object which threw a large amount of material from both bodies into orbit around the Earth (forming the moon)
500
What methods did early geologists use when they first developed the geologic time scale?
geologists studied rock layers, index fossils world wide and placed rock layers in order by relative age
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