The Geologic Time Scale A History of Earth and Life

Evolution Standards 7a. Know why natural selection acts on the phenotype rather than the genotype of an organism. 7b. Know why alleles that are lethal in a homozygous individual may be carried in a heterozygote and thus maintained in a gene pool. 7c. Know new mutations are constantly being generated in a gene pool. 7d. Know variation within a species increases the likelihood that at least some members of a species will survive under changed environmental conditions. 8a. Know how natural selection determines the differential survival of groups of organisms.

8b. Know a great diversity of species increases the chance that at least some organisms survive major changes in the environment. 8c. Know the effects of genetic drift on the diversity of organisms in a population. 8d. Know reproductive or geographic isolation affects speciation. 8e. Know how to analyze fossil evidence with regard to biological diversity, episodic speciation, and mass extinction.

Geologic Time Scale Division of Earth’s history into blocks of time

1. Relative Dating Trying to determine which rock units formed first, second, third, & so on… Forming a sequence of time…no dates!

Rules for Relative Dating 1. Rocks on the bottom are older than rocks on top Law of Superposition

2. Principle of Original Horizontality Layers of rock are generally deposited in a horizontal positions

3. Rock that cuts through is younger than the rock it cuts Principle of Cross-Cutting

Matching Rock Layers Correlation To make a time scale we have to be able to find similar rock in different areas

Fossils also help… What are fossils? Remains or traces of an organism that have been preserved

Types of fossils 1. MOLD – created when an organism is buried in sediments & is dissolved by underground water

Types of fossils 2. CAST – Created when the hollow spaces of a mold are filled with mineral matter

Types of fossils 3. CARBONIZATION – occurs when an organism is buried under fine sediment. Pressure causes only a thin residue of carbon to be left. Best for preserving leaves & delicate animals

Types of fossils 4. Impression – a replica of the surface that occurs when the carbon film is lost.

5. Amber – Created when organisms are preserved in tree sap (resin) Types of fossils

6. Petrified – Occurs when minerals from water replace the organism “turned to stone”

Biogeography Study of the geographical distribution of fossils & living organisms

2. Absolute Dating Radiometric Dating & Radiocarbon Dating Radioactive decay is used to date fossils. This gives us a specific time that the organism died.

Earth is about 4.6 billion years old

Mass Extinction 248 mya 95% Marine species extinct; 70% land species extinct

Mass Extinction 65 mya 85% of all species extinct

How do we know there was a mass extinction? Lots of fossils in one layer & no more of those fossils above it. Lots of new species of fossils in the layers above this