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Arrow_left - Earth History and Geologic Time Scale
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a random change in an organisms' DNA, which results in that organism having a different trait or characteristic
a characteristic that an organism has (examples: brown fur, blue eyes, long neck, etc.)
law of superposition
the law which states that the further down you dig, the older the rocks (and fossils) are.
natural selection
the slow process by which organisms adapt to new environmental pressures, sometimes referred to as "survival of the fittest."
Developed by Charles Darwin, this theory states that organisms change very slowly over time to become more advanced new species. This process is driven by natural selection.
An organism from which another has descended
an organism that has descended from an ancestor
common ancestor
When two organisms evolved from the same organism we call that organism their ___________ ___________.
An organism that has a backbone
An animal that has no backbone
Cambrian Explosion
A period of time during the Paleozoic Era when many marine invertebrates evolved and appeared in the fossil record for the first time
geologic time scale
How scientists measure Earth's long history
Paleozoic Era
"Ancient life." This was the first era after Precambrian time, when many group of animals were evolving, including invertebrates, and the first vertebrates
Mesozoic Era
"Middle life," The Age of Reptiles, when dinosaurs evolved and became extinct at the end
Cenozoic Era
"Recent Life," The Age of Mammals, characterized by several dramatic changes in climate and periodic ice ages
The second period of the Mesozoic
The first period of the Mesozoic, dinosaurs and mammals appear in the fossil record for the first time
The third and final period of the Mesozoic Era which ended in a mass extinction
Permian extinction
The largest mass extinction of Earth's history, took place at the end of the Paleozoic, over 95% of marine life became extinct
Eras are broken down into smaller chunks called ___________.
Periods are broken down into smaller chunks of time called ____________.
mass extinction
When a large number of species become extinct within a relatively short period of time.
environmental pressure
Any factor that makes it more difficult for organisms to survive (limited food, water, space, predators, etc.)
A characteristic that helps an organism survive the process of natural selection
giant supercontinent that broke apart during the Mesozoic Era.
an animal that lives part of its life on land and part under water
a vertebrate with scaly skin, that lays eggs, some have a shell
a warm-blooded vertebrate that feeds its young milk (examples: mice, humans, tigers, bears, horses, elephants, sloths, etc.)
Tertiary Period
The first period in the Cenozoic Era
The second period of the Cenozoic Era, the one we are living in now
radioactive dating
a method scientists use to figure out a rock or fossils absolute age
relative age
The age of a rock or fossil compared to other rocks or fossils
absolute age
the exact number of years since a rock or fossil formed
index fossil
fossils of widely distributed organisms who lived during a known amount of time