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Geologic Time (Ch 8)

Name:________________________
Class: ___________ Date: ________
Across
Preserved remains can be found in ______, which is the substance made from hardened tree resin.
Earth early atmosphere may have included light gases such as _______ and helium.
Preserved _____ are found when entire organisms are preserved.
During _____ decay, the atoms of one element break down to form atoms of another element.
Scientist have determined that Earth is about 4.6 _______ years old.
______ is the change in living things over time.
The ______ age is the number of years that have passed since the rock formed.
Geologist use the law of _____ to determine the relative ages of sedimentary rock layers.
______-14 is used to date fossils.
The geologic time _____ is a record of the geologic events and the evolution of life forms as shown in the fossil record.
Organisms could live on land after the _____ layer formed, that blocked the ultraviolet rays of the sun.
Scientists who study fossils are called _______.
Scientist use the rate at which radioactive elements _____ to calculate the age of rock.
A/An ______ is a unit of time that subdivides eras.
A carbon ______, is type of fossil that is a extremely thin layer of carbon on a rock.
When the Earth was forming, denser materials sank toward the center, forming Earth's dense iron _____.
At the beginning of the _____ Era, a great number of different kinds of organisms evolved. For the first time, many organisms had hard parts including shells and outer skeletons.
A fossilized _____ is one example of a trace fossil.
The earliest known life forms on Earth were ____ cells organisms.
A _____ is a ball of dust, gas and ice that orbits the sun.
A type of organism is _____ if it no longer exists and will never live again on Earth.
The ______ age of a rock is its age compared to the ages of other rocks.
Down
A ____ is a break in the Earth's crust.
A/An _____ is a long unit of time used to divide the time between Precambrian time and the present.
Preserved remains or traces of living things.
A _____ is a hollow area in sediment in the shape of an organism or part of an organism.
A ____ is a solid copy of the shape of an organism.
During the _____ Era, mammals evolved to live in many different environments - on land, in water, and even in the air.
Many early animals were _____ or animals without backbones.
Scientist hypothesize that a ____ extinction occurred when an asteroid from space struck Earth at the close of the Cretaceous Period.
Reptiles were so successful during the _____ Era that this time is often called the Age of Reptiles.
An ____ fossil is a fossil that is widely distributed and represents an organism that existed for a geologically short period.
A/An ____ is an animal that lives part of its life on land and part of its life in water.
In undisturbed horizontal sedimentary rock layers, the oldest layer is at the ______.
An _____ is a gap in the geological record where rock layers have been lost due to erosion.
______ have scaly skin and lay eggs that have tough leathery shells.
The earliest part of the geologic time scale was named _____ time.
Lava that hardens on the surface and forms igneous rock is called an _____.
Magma that cools and hardens below the surface is an _____.
_____ fossils are fossils in which minerals replace all or part of an organism.
The _____ of a radioactive element is the time it takes for half of the radioactive atoms to decay.
A fault is always _____ than the rock it cuts through.
_____ fossils provide evidence of the activities of ancient organisms.