| A | B |
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| mold fossil | forms when sediments bury an organism and the sediments change into rock; the organism decays leaving a cavity in the shape of the organism. |
| cast fossil | forms when a mold is filled with sand or mud that hardens into the shape of the organism. |
| Petrified fossil (permineralized fossil) | – forms when minerals soak into the buried remains, replacing the remains, and changing them into a mineral/rock replica. |
| Carbonized fossil | forms when organisms or parts, like leaves, stems, flowers, fish, are pressed between layers of soft mud or clay that hardens squeezing almost all the decaying organism away leaving the carbon print on the rock. |
| Trace fossil | gives clues as to the activities of an organism; forms when the mud or sand hardens to stone where a footprint, trail, or burrow of an organism was left behind. |
| a fossil | is the preserved remains or traces of an organism that lived in the past, usually more that 10,000 years ago. Fossils give clues to the diversity of living things over the history of Earth, give clues to past climate and surface changes on Earth, and give clues to changes that have occurred with organisms over time. |
| adaptation | is a trait or behavior that helps an organism survive and reproduce. |
| Natural selection | is the process that explains this survival and shows how species can change over time. For example, certain traits or adaptations involving color, camouflage, food gathering (beaks, claws) and other physical traits, sensory abilities, or behaviors enhance the survival of a species. |
| Changes in life forms, additions and extinctions, are often accompanied by changes in environmental conditions on Earth. | These environmental changes have been influenced by the impact of an asteroid or comet, climatic changes, and volcanic activity. |
| At the end of the Mesozoic Era, when reptiles, early birds and mammals thrived, many groups of animals disappeared suddenly. | At the end of the Mesozoic Era, when reptiles, early birds and mammals thrived, many groups of animals disappeared suddenly. |
| Climatic changes | Climate is an ever-changing condition on Earth. |
| examples of climate change | Life on land developed and flourished in the tropical climates and warm shallow seas during the Paleozoic Era. Throughout this era as different land environments formed and sea levels changed, new life forms developed. Other life forms that could not adapt or find suitable conditions, especially many marine species, disappeared. |
| Volcanic activity | During the Precambrian time volcanic activity was one of the most natural events, but lava flows, ash clouds in the atmosphere, and heat made conditions for life forms extremely difficult. Those simple life forms often did not survive these conditions. |
| eras | eras are divided into periods |
| periods | periods can be further divided into epochs |
| Major information found on the geologic time scale includes: | Precambrian Eon is the name given to the earliest and longest span of time in Earth history. |
| geological time scale | The geologic time scale is a record of the major events and diversity of life forms in Earth’s history. |
| Paleozoic Era | Began with the early invertebrates, such as trilobites and brachiopods; continued to develop early vertebrate fish, then arachnids and insects; later came the first amphibians, and near the era’s end the reptiles became dominant. |
| Mesozoic Era | Reptiles were the dominant animals of this era, including the various dinosaurs. |
| Cenozoic Era | New mammals appeared while others became extinct. |
| relative age | the age of one object compared to the age of another object. Relative age does not tell the exact age of an object. The relative age of rocks and fossils can be determined using two basic methods: ordering of rock layers and index fossils: |
| absolute age | means determining the number of years since the object was formed. The absolute age of igneous rocks can be determined using radioactive decay (also called radiometric dating). |
| Ordering of Rock Layers | Scientists read the rock layers knowing that each layer is deposited on top of other layers. |
| index fossils | can be used to help find the relative age of rock layers. To be an index fossil.an organism must be unique and have lived only during a short part of Earth’s history) |
| excinction | A species is extinct if no members of that species are still alive. Most organisms that have ever lived on Earth are now extinct. |
| natural factures | can cause extinctions such as has happened throughout Earth history. |
| Uniformitarianism(by hutton) | is the idea that processes that operated in the remote geological past are not different from those observed now. |
| man-made factors | have caused extinctions in more recent times, such as the cutting of the rainforest regions, removing natural habitats, over-harvesting, and pollution |
| natural excinction | Organisms that could not survive changes due to volcanic eruptions and global warming, global cooling during ice ages, changes in oxygen levels in seawater or atmosphere, or a massive impact from an asteroid or comet became extinct. |
| huttons theory | uniformitarianism:eart is an always cahnging place the same forces of change at work today as in the past |
| geoligical time scale | divides eartsh history into intervals of time defined by major events or changes on earth |
| eon | largest unit of time |
| era | eons may be divided into eras(four are the paleozocic,the mesosoic, and the cenozoic |
| period | each ara is subdivided into a number of periods |
| epoch | the periods of the cenozoic the most recent are farther divided into epoches |
| best preseritives | tar, ice, amber |
| igneous rocks | igneous rocks never contain fossils |
| relative dating | not exact, greator or younger or older |
| absolute | exact age |
| halfe life | the length of time it takes for half of the atom in a sample of a radioactive element to change from an unstable form into another form |
| radioactive dating | works best for ignous rocks |
