1. Petrified fossils: formed by replacement. Water carrying minerals replaces all or part of an organism. 2. Molds and Casts: Mold: hollow area in sediment in the shape of an organism Cast: water carrying minerals seeps into the mold and deposits the minerals
* 3. Carbon films: As a buried plant or animal decays, it releases gases containing carbon. The gases escape, leaving the carbon behind preserving the plant or animals image.
4. Trace fossils: evidence that an organism was previously there and left evidence activity. Example: footprints, trails, burrows
1. The fossil record provides evidence about the history of life on Earth. The fossil record can tell us about past environments and climate change on Earth. The fossil record can tell us about mass extinctions.
2. The fossil record shows how organisms have changed over time. (evolution) It shows how organisms have gone from simple to more complex organisms.
Rock layers provide a record of Earth’s geologic history.
Relative age is the age of a rock compared to the ages of other rocks. (Older or younger to other rocks). Geologists use the law of superposition to find a rock’s relative age. (OLDER ROCK LAYERS ARE AT THE BOTTOM-EACH LAYER ABOVE IS YOUNGER THAN THE ONE BELOW).
An extrusion is lava that cools and hardens on Earth’s surface (Extrusive Igneous Rock). Rock layers below an extrusion are older than the extrusion. An intrusion is magma that cools and hardens under Earth’s surface (Intrusive Igneous Rock). An intrusion is always younger than the rock above or below it.
A fault is a break in Earth’s crust. Forces inside the Earth cause movement of the rock on both sides of a fault. A fault is always younger than the rock it cuts through.
Folding and erosion cause unconformity as newer rock layers blend with older layers.
Geologists use the relative age of rock layers to determine the age of the fossils within those layers.
Index fossils are widely distributed and existed for a brief period of time. These fossils also give us clues to a rock layer’s relative age. Certain types of trilobites (large-eyed) existed after other trilobites became extinct.
Define the following: Relative age Absolute age Law of superposition Extrusions Intrusions Unconformity Index fossil
Relative age: the age a rock compared the age of surrounding rocks Absolute age: the age of a rock since it was formed Law of Superposition: in horizontal rock layers, the oldest is always on the bottom.
- extrusions: lava that hardens on the surface - always younger than the layer below it - intrusions: magma that hardens below ground - dike: always younger than the rock layer it cuts across - unconformity: a gap in the geologic record - missing layer(s) usually due to erosion
-index fossil: a fossil that can be used to determine the relative age of rock layers - fossil must be widely distributed and should have existed for a short period of time. Fossils record shows how life has become more complex. Example : trilobites, ammonites
A. rock layers are deposited horizontally. B. rock layers on the bottom are the oldest. C. rock layers on the top are the oldest. D. I don’t know
A. when extinct organisms lived B. what extinct organisms behaved like C. the year they died D. I don’t know