Earth

Absolute Dating
- Determines the number of years old something is.
Relative Dating
- Used to determine if one thing is younger or older than another.

Radioactive Dating: Measures the time since a rock or fossil formed through the decay of radioactive isotopes.

Law of Superposition:
- Sediments are laid down underwater in historical layers forming sedimentary rocks.
Use of Index Fossils: Fossils that help date rock layers.
Correlation of Rock Layers: Comparing rock layers from different locations to determine their relative ages.

Basic Principle:
- In a series of sedimentary rocks, the bottom layer is the oldest, and the top layer is the youngest.
- Lower layers must be in place before younger rocks can be deposited on top of them.
- There are exceptions, such as geological events which can overturn layers.
Fossils:
- Fossils are generally the same age as the rock layers they are found in.
- Animal remains are deposited along with the sediment which will eventually turn into sedimentary rocks.

Fossils:
- Naturally occurring preserved remains or impressions of living organisms.
- Usually only the hard parts are preserved, including bones, teeth, and shells.
- Hard parts may be replaced by naturally occurring minerals over time.
- The organism that created the fossil lived during the time the rock layer was forming, specifically when the sediment was being deposited.
Common Findings:
- Generally found in sedimentary rock layers.

Ancient Environment Indicators:
- Marine fossils indicate a marine environment.
- Woolly mammoths indicate a cold environment, etc.
Fossil Record Insights:
- Shows a wide variety of plants, animals, and simpler life forms that have lived on Earth in the past.
- Indicates that life forms have evolved over time, with most life forms of the geologic past having become extinct.

Index Fossils:
- Used to date rock layers (strata).
- Derived from creatures that existed for a relatively short geological period.
- Exhibited wide geographic distribution.

Definition:
- The process by which an unstable radioactive element transforms into a stable element.

Method:
- The age of objects can be determined by measuring the relative amounts of radioisotope and decay products.

Body Fossils:
- Any actual parts of an organism: bones, teeth, shells, claws.
- Historical Notables:
- The first dinosaur bone was found in 1818.
- The first complete skeleton was found in 1858 in New Jersey.
- Sometimes, bits of broken teeth of carnivorous dinosaurs are found alongside other dinosaur bones.
Cast Fossils:
- Formed when the mold created by the organism fills in, creating a raised surface.
- Often found in sandstone and other porous rock types.
- Commonly found examples include arthropods, such as trilobites and other ancient species.
Mold Fossils:
- Fossilized impression (depressed surface) of the actual organism.
- Forms when an organism's hard parts are buried in mud or clay, dissolving, while the surrounding material hardens into stone, leaving an impression.
- Create negative impressions due to surface depression.
Trace Fossils:
- Fossilized imprints of an organism's tracks (footprints), trails, burrows, or nests with eggs.
- Most common type of fossils because an organism can leave behind thousands of prints while leaving only one body.

Footprints provide valuable information about:
- Speed of animals.
- Length of stride.
- Bone structure.
- Stalking behavior and other behavioral patterns.

Definition:
- Hardened resin (such as amber) produced by extinct coniferous trees.
Formation:
- During its life, resin is sticky and flows slowly, but after millions of years, it hardens into amber.
Significance:
- The oldest amber resin fossils date back more than 320 million years.
- Organisms sometimes get trapped within the amber, providing extensive information about those organisms.