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Earth's History

A Trip Through Earth's History

A fossil is ______________. the preserved remains or traces of an organism
How do most fossils form? Living things die and their remains are buried by sediment
A fossil is formed when minerals replaced all or part of an organism called a ______________. petrified fossil
______________ can provide clues about the activities of ancient organisms. trace fossils
The process by which all the different kinds of living things have changed over long periods of time is called ______________. evolution
A type of organism that no longer exists on Earth is said to be ______________. extinct
The relative age of a rock is ______________. its age compared to the age of other rocks
The law of superposition states that, in horizontal layers of sedimentary rock, each layer is ______________. older than the layer above it and younger than the layer below it
The fossils of organisms that were widely distributed but only lived during a short period of time are called ______________. index fossils
Radioactive decay occurs when atoms of an unstable element ______________. break down to form atoms of another element
Radioactive dating enables geologists to determine ______________. the absolute age of rocks
The Paleozoic, Mesozoic, and Cenozoic are divisions in the geologic time scale called ______________. eras
The geologic time scale is a record of ______________. the life forms and geologic events in Earth's history
The earliest life forms were ______________. is di single-celled organisms
The evolution of photosynthetic organisms that lived 2.5 billion years ago led to ______________. an increase in oxygen in the atmosphere
The end of the Paleozoic was marked by the ______________. Permian extinction
The first vertebrates were ______________. jawless fish
Many scientists hypothesize that the dinosaurs became extinct because ______________. an asteroid hit earth, throwing dust into the atmosphere and cooling the climate so that the dinosaurs could not survive
Fossils usually occur in ______________ rock. sedimentary
On the geologic time scale, the ______________ Era is divided into the Triassic, Jurassic, and Cretaceous periods. Mesozoic
A(n) ______________ fossil forms when dissolved minerals replace the remains of an organism then then harden to form rock. petrified
Plant leaves may form a fossil called a(n) ______________, a thin layer of carbon on rock. carbon film
______________ are scientists who study fossils.
A rock layer's ______________ age is its age compared to the age of other rock layers. relative
A(n) ______________ is a gap in the geologic record where some rock layers have been lost because of erosion. unconformity
Certain ammonites are used as ______________ fossils because they lived in many different areas but for only a brief time. index
The time it takes for one half of the atoms in a sample of a radioactive element to decay is called the element's ______________. half-life
Geologic time begins with the long span of time called ______________ Time. Precambrian
The present day is part of the ______________ Era. Cenozoic
The ______________ Era is sometimes referred to as the "Age of Reptiles." Mesozoic
How is a cast fossil formed? soft part of animal decays and minerals slowly fill in space
How is it possible for an organism to have very little change since its death 10,000 years ago? it was preserved when it was trapped in tar, ice, or amber
Created by: Pacelli