Scientists have determined the age of the Earth to be about 4.6 billion years old 4,600, 000, 000 years = 4.6 x 10 9 years (scientific notations you should know) 10 9 = billion 10 6 = million 10 3 = thousand = trillion For example, 10 9 can be read as “one with 9 zeroes after it”OR 1,000,000,000

Prior to the discovery of radioactivity, geologists had no reliable method of giving specific dates to geologic events and had to rely on relative dating techniques. Relative Dating means placing rocks or events in their proper sequence of formation, based on a comparison to other rocks

Principle of Original Horizontality states that sediments are deposited in horizontal layers Layer 1 – Siltstone Layer 2 – Limestone Layer 3 – Sandstone

Law of Superposition states that in an undeformed sequence of strata, each bed is older than the one above it and younger than the one below it.

What a Regents Question might say… This question may require the use of the Earth Science Reference Tables. Base your answer to this question on the geologic cross section below. Overturning has not occurred. The dike and sills shown in the cross section are igneous intrusions. Which rock type is the oldest?

Intrusions are younger than the rocks that they intrude

Extrusions are younger than the rocks they form above.

Buried erosional surfaces that are preserved in the rock record Unconformities represent gaps in the geological record in the rocks

Correlation is the process of matching rock units or events in separate rock formations Correlation of rock units and geologic events can be based upon continuity, similar rock composition, fossil evidence, and volcanic markers.

Fossils can be used to help match separate rock layers Unconformity

Index Fossils – a fossil of an organism that lived over a wide geographic area for a relatively short period of time This ensures that the fossils will have a wide horizontal and small vertical distribution throughout the rock record

Age of rock or geological event in years before the present (as opposed to relative ages). Common units are: millions of years ago = m.y. = 10 6 billions of years ago = b.y. = 10 9 Not just using tree rings! We have another, more effective technique! Absolute Age (Absolute Dating)

The rate of decay (breakdown) for any radioactive isotope is constant. Over a given period of time, a definite fraction of the atoms of an isotope will decay.

The time required for half of the atoms in a given mass of an isotope to decay is known as the half-life of the isotope. Each radioactive isotope has its own characteristic half-life, which is not affected by any environmental factors (T, P, or chemical reactions), mass or volume. If you cut the isotope into pieces, or heat it up, there is NO CHANGE in half-life!

The method of using the half-life of a radioactive isotope to determine the absolute age of a material. The ratio between the amount of the original isotope (Parent Material) and the amount of its decaying product (Daughter Product), is used to establish the absolute age of a sample.

Key OtherC 14 N 14 Carbon Dating 0 Half-Life

Key OtherC 14 N 14 Carbon Dating 1 Half-Life (5,700 years)

Key OtherC 14 N 14 Carbon Dating 2 Half-Lives (11,400 years)

Key OtherC 14 N 14 Carbon Dating 3 Half-Lives (17,100 years)

Key OtherC 14 N 14 Carbon Dating 4 Half-Lives (22,800 years)

Key OtherC 14 N 14 Carbon Dating 5 Half-Lives (28,500 years)

Key OtherC 14 N 14 Carbon Dating 5 Half-Lives (28,500 years)

Igneous and metamorphic rocks work excellent for radioactive dating because at the time of crystallization (or recrystallization), a specific ratio of stable and radioactive isotopes are incorporated into the crystals. On the other hand, sedimentary (clastic) rocks do not work well because they are composed of older, pre-existing rock fragments.

Carbon-14 (C 14 ) Carbon-14 dating – also called radiocarbon dating – can be used to date remains that contain carbon up to 70,000 years old. This method has been used to date early humans, mastodonts, and many other geologically “recent” organic remains.

Origins of our Solar System

Earth formed through the gravitational attraction and accumulation of asteroids and rocky debris This accretion of material generated a tremendous heat causing the planet to be molten The denser materials settled into the interior and the Earth’s layered internal structure formed.

Evidence from the fossil record (preserved in sedimentary rocks) shows that a wide variety of life forms have lived in Earth’s changing environments over time.

The comparisons of fossil remains and current life forms enable scientists to make predictions about the Earth’s past environment. A major reason for changes in Earth’s environment over geologic time has been the movements of plates and their associated landmasses.

The theory of organic evolution states that life forms change through time. As environmental conditions change, variations within a species give certain individuals a greater chance for surviving and reproducing. These variations, along with others get passed on to future generation leading to the creation of a new species.

The fossil record provides evidence for the theory of organic evolution. This also shows that evolution does not always occur at the same rate. There are times of rapid extinctions and subsequently rapid evolution of new species.

Precambrian (4.6 b.y m.y.) – Simple organisms (invertebrates) – “Soft-Bodied” Organisms (Fossils are rare)

Paleozoic (544 – 251 m.y.a.) –Organisms proliferate and become more complex (vertebrates) –Shelled (mineralized skeletons and shells) organisms develop –(Brachiopods/Trilobites) –Amphibians develop from lobe-finned fish –Era ends with a mass extinction killing off more than 95% of the life on earth

Mesozoic Life ( m.y.a.) – “Age of Reptiles” (dinosaurs, flying reptiles and birds develop) – Modern animals and plants begins to develop on land – Era ends with a mass extinction killing off dinosaurs, ammonoids, flying reptiles, and some swimming reptiles.

Cenozoic Life (65 m.y.a. – present) – “Age of Mammals” (mammals begin to develop and evolve) – Humans develop from primates (Homo Habilus 1.6 m.y.)

Topic 14: Landscapes

Drainage Patterns