Term | Definition |
Eon | the largest group; divided by the CAMBRIAN BOUNDARY (about 550 million years ago) when the variety of life forms explodes; billions of years ago |
Era | mass extinctions mark the boundaries between the eras; hundreds of millions of years long |
period | blocks of time when a unique rock series was laid down; tens of millions of years long |
Epoch | divisions of the most recent periods; several million years ago |
molds and casts | acids eat away the skeletonor shell and leave an impression (mold) in the rock; if the mold fills with minerals, it becomes a cast |
tracks and trails | imprints are left in mud which later hardens; dinosaur tracks are fairly common |
carbonization | oils leave the plant, and the remaining matter becomes a layer of carbon; in other cases, nitrogen, hydrogen, and oygen are distilled from the plant; most common method of fossilizing plants |
petrifaction | minerals in plant cells crystallize; minerals enter openings or cavities in shells or bone; common with plants |
replacement | object buried in mud has its molecules replaced by minerals; rare |
recrystallization | mineral aragonite in shells turns into calcite; preserves the general shape of the animal |
soft tissue preservation | mummification, frozen in ice |
traps | whole organisms locked in tar pits, asphalt, amber, ect. |
cenozoic | quaternary, tertairy, halocene, pleistocene, pliocene, miocene oligocene, eocene, palecene |
mesozoic | cretaceous, jurassic, triassic |
paleozoic | permian, carboniferious, devonian, silurian, ordovician, cambrian |
precambrian | proterzoic, archaean, hadean |
fossil | are the imprints or remains of organisims that were once alive |