Chapter 10 Clues to the Earth's Past

Chapter 10

Clues to the Earth's Past

Trace Fossils

• Trace fossils provide so much information about how an organism lived because the tracks can give scientists hints about an organism's lifestyle.

Fossil

• How well an organism is protected from scavengers, decomposers, and physical agents that break things down determines whether or not an organism will become a fossil.

Who studies Fossils?

•  A paleontologist studies fossils.

Fossils

Natural preservatives have helped scientists discover fossils found in amber, frozen ground, and tar.

What principle did James Hutton use to determine that Earth was much older than a few thousand years old?

James Hutton used uniformitarianism to determine that Earth was much more than a few thousand years old.

Superposition

The principle of superposition states that older things on are the bottom, and younger ones are closer to the top.

Relative Age

The relative age of something is its age in comparison to other things.

Rock Layers

Scientists use radioactive decay, half-life, and fossil evidence to determine the correlation of rock layers.

How do unconformities form?

Unconformities occur when erosion removes portions of rock by washing or scraping them away.

Nonconformity

When sedimentary rock is deposited on top of igneous or metamorphic rock, scientists call this nonconformity.

Rock Record

A disconformity in a sedimentary rock sequence represents a gap in the rock record.

Absolute Ages

Scientists use the properties of the atoms, rocks, and other objects to help them determine their absolute ages.

Radiometric Dating

Radiometric dating uses ratios to help determine the absolute ages of rocks.

Radiometrically Dated

Rocks that can be dated radiometrically are mostly igneous and metamorphic rocks.

Oldest Rocks

Radiometric dating has been used to date the oldest rocks on Earth, and scientists now estimate Earth to be 4.6 billion years old.

Trace Fossils

This is an example of how a trace fossil might provide information about behavior of an ancient animal.

Mold

A mold is an imprint made in sediment by the organism.

Cross-cutting relationships

The principle of cross-cutting relationships indicates that the fault line appeared most recently. The principle of inclusions indicates that the magma intrusion happened after all of the rock layers were in place. Finally, the principle of superposition describes the order in which the rock layers were first deposited.

Fossils

Fossil 2 is the oldest, fossil 1 is in the middle, and fossil 3 is youngest.

Absolute Dating

Fossil C is in a rock layer that is between 120 and 280 million years old.

Rock Record

Information that is missing from the rock record at one site might be deduced from corresponding, or correlated, rock at another site.