| A | B |
|---|
| Cenozoic Era | the present geologic time period,beginning 65 million years ao |
| dinosaur | a group of extinct reptiles that lived during the Mesozoic Era ; and whose name means ''terrible lizard" |
| Mesozoic Era | an era from 225 to 65 million years ago,during whichmammals ,birdsand flowering plants developed |
| geologic time chart | a written listing of Earth's history, including geological events and the evolution of life |
| theory | an explanation or model based on observation, tests and reasoning to help explain an occurrence |
| era | the largest unit of geologic time |
| extinction | when all members of a life form die |
| period | the major subdivision of an era in geologic time |
| physical events | major events occuring on the Earth's landmasses, such as mountain-building and erosion |
| amphibian | a cold-blooded animal living both on land and in the water, has moist skin and lays its eggs in water |
| invertebrate | an animal without backbone, such as worms, insects and microscopic animals |
| vertebrate | an animal having a backbone, including all fish, amphibians, reptiles, birds and mammals |
| evolve | to develop naturally, without the help of humans |
| evolution | the theory that all living things developed slowly over millions of years from simpler forms of life |
| Paleozoic Era | the geologic time peroid, from 570 to 225 million years ago, in which fish, land plants, amphibians, reptiles and insects appeared |
| Precambrian Era | the first and by far the longest geologic time peroid, lasting from 4.6 billion to 570 million years ago |
| protein | large complex molecules made up of carbon, hydrogen, oxygen and nitrogen; sometimes called the "building blocks of life" |
| convergent evolution | evolution in which forms of life from different beginnings start to look like each other, and fit into the same habitat |
| straight-line evolution | evolution in which forms a life form can be traced from one generation to the next with little change |
| fossil | the hardened remains of an animal or plant from an earlier age usually preserved in rock |
| paleontologist | a scientist who traces the Earth's history and its life forms by studying fossils |
| skeleton | the framework of bones supporting an animal's muscles and organs and giving it a basic shape |
| unconformity | a boundary line between two different geologic time peroids, existing either in the rock or fossil types |
