"Turned to stone" minerals replace all or part of the organism
hollow area in sediment in the shape of an organism
a copy of the shape of an organism
extremely thin coating of carbon on rock, gases from decaying organisms escape into the sediment leaving behind a thin layer of carbon
evidence of activities of past organisms, footprints, burrows
tar, amber (petrified tree sap), frozen remains (like the woolly mammoth
the gradual change of living things over time
a well tested concept that explains a wide range of observations
an organism that no longer exists, and will never again live on Earth
Five types of fossils that can be found in rock
carbon film, mold and cast, petrified, preserved remains, trace
for a rock, is the age compared to the age of other rocks
for a rock, the exact (as possible) number of years since the rock formed
First Clues to relative age
The Law of Superposition- in horizontal layers of sedimentary rock the oldest layers are at the bottom. Each higher layer is younger than the layer below
Second Clues to relative age
Igneous rock Extrusion 1. layer once on the surface 2. layers below are always older
Clues to relative age
Igneous rock Intrusion 1. welling uplift of magma that went through layers 2. intrusion is always younger than the layers around the intrusion and layers below an intrustion
break in the Earth's crust- The fault is always younger, than the layers of rock the fault cuts through.
A gap in the geologic record. Some layers have been lost due to erosion. New rock layers are on top of very much older layers.
Used to date the relative ages of the rock layers they are found in.
Requirements to be an index fossil
1. Organism must be widely distributed (was found nearly everywhere on Earth) 2. Organism that existed only briefly, then died out.
fossilized bacteria grew like stacks of pancakes, estimated at 3 billion years old, one of the oldest living things found on Earth.
Atoms of one element breakdown to form more stable atoms of another element. The rate of decay of each different radioactive element is constant- it never changes.
The time it takes for half of the radioactive element to decay.
Why do scientists use radioactive dating
To determine the absolute ages of rock
Dating is useful for dating ancient rock half-life of 1.3 billion years
Dating is useful up to 50,000 years because of its short half-life of 5,730 years
How old is Earth?
A little older than 4.6 billion years is currently accepted
Provides evidence of the history of life on Earth. Shows that different groups of organisms have changed over time.