What is a comet?
A ball of dust, gas, and ice that orbits the sun
Why do geologists use the geologic time scale?
Because the time span of Earth's past is so great
What is the first major division of geologic time?
Precambrian time
What gases composed the first atmosphere?
Light gases like hydrogen and helium
What is an invertebrate?
An animal without a backbone
How did Earth's oceans form?
As the atmosphere cooled, water vapor condensed into rain which fell and formed the oceans
How do scientists think that the Earth formed?
They think it began as a ball of dust, rock ,and ice in space that was pulled together by gravity
What is an amphibian?
A vertebrate that spends part of its life in the water and part of its life on land
What are the three divisions of time between Precambrian Time and the present called?
Eras
What is a mass extinction?
When many types of living things become extinct at the same time
How did Earth's environments change from the Neogene to the Quaternary Period?
The climate began to cool causing ice ages
What were the earliest multi-cellular organisms?
Invertebrates
Did humans and dinosaurs ever live together? Why?
No; dinosaurs went extinct at the end of the Mesozoic Era, and humans did not evolve until the Quaternary Period
Aside from respiration, why was the release of oxygen during photosynthesis important to land animals?
The oxygen formed the ozone layer which protects Earth from ultraviolet rays from the sun
What is a reptile?
A vertebrate that has scaly skin and lays eggs with tough, leathery shells
During which era did mammals evolve to live in many different environments?
Cenozoic
What information do scientists infer from fossils?
How organisms and environments have changed over time
What is the most recent period of geologic time?
The Quaternary Period
What is a vertebrate
An animal with a back bone
During which era did reptiles spread widely?
Mesozoic
What are eras subdivided into?
Periods
What is a mammal?
A vertebrate that can control its body temperature and feeds milk to its young
How did scientists develop the geologic time scale?
By studying rock layers and index fossils