L1 ESCI 2020

Hypothesis

→ An educated guess, based on observation that can be supported or refuted through experimentation or more observation.

Model

Hypothesis that has at least limited validity

Law

Description of natural phenomenon that invariably holds true under specific conditions and will occur under certain circumstances

Theory

A scientifically accepted general principle supported by a substantial boy of evidence offered to provide an explanation of observed facts and as a basis for future discussion or investigation.

Uniformitarianism

• James Hutton & Charles Lyell

• Present key to the past

• Processes happening today can help us understand processes that happened in the past.

Estimated Age of the Earth is _________ and was determined using _________ _________

• 4.55 billion years

• Radiometric Dating

Relative Age Dating Starts with

Stratigraphy

Stratigraphy

• Description, correlation, and classification of strata in sedimentary and layered rocks

What are the principles of statigraphy?

→ Original Horizontality

→ Superposition

→Cross Cutting

What does original horizontality state

What does superposition state

• oldest on bottom, younger above

What does cross cutting tell you?

-            If geological feature A cuts across geological feature B, then B is older than A.

o   If something is broken by something else, the thing that is broken is older.

What does an unconformity represent?

• a gap in the geologic record, identified using principles of stratigraphy.

• angular unconformity - horizontal layers deposited, tilted, erosion, new layers, angled layers older.

What is faunal succession?

-            Organisms change / evolve over time and appear in definite & invariable sequence in the geologic record.

o   Therefore their preserved remains can be used to identify the relative age of rock units.

Fossils

remains / traces of a plant / animal preserved in Earth’s crust

What are the 3 traits of an index fossil?

1.        Geographically widespread

2.        Geologically short existence

3.        Morphologically distinct

Any time period can be recognized by its ____ _____ because organisms evolve in a definite and determinable order.

Fossil content

Fossils can be used to identify _____ _____ of rock units becuase of _____ _____

Relative Age

Faunal Succession

Why are fossil assemblages useful?

Even if fossils have long stratigraphic ranges, fossil assemblages with narrow ranges can be used by examining overlapping ranges.

How can fossils correlate strata?

Geologic time scale built using

Faunal succession

The geologic time scale ____ strata using fossils and fossil assemblages found within rock units

Correlates

What is radiometric dating?

• uses concept of radioactive elements having a consistent decay rate measuring ratio of parent v daughter isotopes to provide an actual numerical age of rock/event

Radioactive decay is______ for a given isotope and is expressed as the ____ _____

constant, half life

Alpha Decay

lose a chunk of nucleus, big drop in atomic weight

Beta Decay

neutron becomes proton, weight does not change but the atomic number does due to going up in protons.

Relative dating

Puts events in sequence.

Lithostratigraphy

-            Relationship of one body of rock to another

-            Each layer is a different rock type.

Chronostratigraphy

-            Temporal relationship between rock units

-            Each layer is a different age

Biostratigraphy

-            Method of relative age dating using the presence of fossil organisms found within strata

-            Each layer contains different fossil assemblage.