Building the Geologic Timescale 1 8 mya 65

Building the Geologic Timescale 1. 8 mya 65 mya 245 mya 545 mya

LAW OF SUPERPOSITION - STENO In a layered succession of strata, any individual unit will be younger than the one below it and older than the one above it, unless the rocks have been folded or overturned.

LAW OF SUPERPOSITION Younger Older

The Law of faunal Succession - Smith In the geologic record, fossil faunas succeed on another in an orderly and determinable fashion. Therefore, rocks of different ages have different fossil faunas.

The Principle of Fossil Correlation –Smith & Cuvier Similar assemblages of fossils are similar ages, and thus the rocks that contain them are of similar ages.

Law of Cross-Cutting Relationships – Hutton A rock unit or structure is older than any rock unit or structure that cuts across it. Law of Inclusions – Steno A rock or fossil that occurs as an inclusion within another rock must be older than the rock that surrounds it.

Fig. 5. 1

UNCONFORMITIES Evidence of missing time in the Geologic Record

Different types of Unconformities Fig. 4. 21

Disconformity Angular unconformity Nonconformity

The Kant/La. Place Hypothesis of Solar System Formation (1755)

The nebula condenses into a swirling disc, p. 26 -27 a with a central ball surrounded by rings. Forming the solar system, according to the nebula hypothesis: A second- or thirdgeneration nebula forms from hydrogen and helium left over from the big bang, as well as from heavier elements that were produced by fusion reactions in stars or during explosion of stars.

The ball at the center grows dense and hot enough for fusion reactions to begin. It becomes the Sun. Dust (solid particles) condenses in the rings. p. 26 -27 b Dust particles collide and stick together, forming planetesimals.

Gravity reshapes the proto-Earth into a sphere. The interior of the Earth separates into a core and mantle. p. 26 -27 c Forming the panets from planetesimals: Planetesimals grow by continuous collisions. Gradually, an irregularly shaped proto-Earth develops. The interior heats up and becomes soft.

Soon after Earth forms, a small planet collides with it, blasting debris that forms a ring around the Earth. The Moon forms from the ring of debris. p. 26 -27 d

RANGES OF EARTH AGES PRE-1900