History of the Earth

CA Standard 8eChapter 17

17-1 The Age of the Earth

• Earth’s age is estimated at 4.6 billion years.

• James Hutton in 1788- proposed that features of the earth were influenced by volcanoes, erosion, etc.. These things all act very slowly

• In 1830, Charles Lyell agreed that the earth had been shaped over a long period of time…but also stressed the importance of explaining theory in terms of scientific method.

Geologic Time Scale• Relative Dating- the age of

some rocks “relative” to others based on their position.

NEWER: RECENTLY DEPOSITED

OLDER: DEPOSITED EARLIER

• Absolute Dating: using scientific techniques to find the approximate actual age of artifacts.

• Radioactive Dating: using the known rate of decay to calculate the age of artifacts. (14C)

Element Half Life

Rubidium-87 50 billion years

Thorium-232 13.9 billion years

Uranium-238 4.5 billion years

Potassium-40 1.3 billion years

Uranium-235 713 million years

Carbon-14 5770 years

17-1 The Fossil Record• Fossils- preserved remains of

ancient organisms

• Formation of fossils- when animals are buried in some medium that prevents decay

–mud, sand, silt, tar pits

–Sedimentary Rock

• Specific conditions are required for fossils to form –mountains vs. rivers and streams

–many organisms never fossilize

• Not all fossils have been found

Problems with the Fossil Record:

• The quality of fossils varies greatly

• As a result, the fossil record is not as complete as paleontologists would like

Cabrian: 500 million

Triassic:

250 million

Jurassic: 200 million

Trilobite

The Fossil Record• Collectively, the millions of

fossils that have been collected make up The Fossil Record

• Many pieces are missing

• Scientists have been able to construct detailed paths of change through time for many species

• Evidence indicates that Earth’s climate has changed significantly over time

• Evidence also shows that species of plants and animals changed to fit those environments, or perished.