Week of February 9

Evolving Planet Interactive

Tour Through Time Link Evolutionary Essentials


Univ. Berkeley Geologic Time

The Big Idea! 

Evidence of the dynamic changes of Earth’s surface through time is found in the geologic record.

I can…

•  Describe methods used by scientists to determine the            age of the Earth
• Describe radiometric dating and its role in absolute age
• Predict age of fossil based on radiometric dating
• Design a graphic representation of the evolutionary               timeline that includes the main geological and evolutionary events that occurred
• Explain how index fossils are used to determine                     relative age

Vocabulary:  

absolute age 
radioactive decay
half-life
radiometric dating
isotope
daughter-atom
neutron
radiation
radioactive
geologic time scale
fossil record
mass extinction
diversity

Absolute Dating of Rock Layers With Index Fossils

• Scientists have estimated the age of the Earth to be approximately 4.6 billion years old.  They have determined this by:

1. The oldest rocks on the Earth have been found in Canada - they are about 4 billion years old
2. Moon rocks and meteorites have been dated at 4.6 billion years old - these bodies would have formed about the same time as the Earth

Radiometric Dating

• Carbon-14 dating is used to date bones, wood, shells, and other organic remains of organisms that lived in the last 45,000 years.  The half-life of Carbon-14 is 5,730 years.  

• Potassium-Argon Dating - finds the absolute age of igneous rock that are between 100,000 - 4.3 billion years old.  (Half-life = 1.25 billion years)
• Uranium-Lead Dating - finds the absolute age of ancient igneous rock  that are 100 million - billions of years old.  (Half-life = 4.5 billion years)

Question:  A sample of volcanic ash was found to have 12.5% of its original radioactive atoms left.  If the half-life of the substance is 20,000 years, how old is the ash?

Geologic Time Comparison

Geologic Time Scale

EON	ERA	PERIOD		EPOCH	MILLIONS OF YRS AGO	MAJOR BIOLOGICAL EVENTS
P H A N E R O Z O I C	C E N O Z O I C	Quaternary		Holocene	.01	Rise of civilization and agriculture. Extinction of large mammals in northern hemisphere.
				Pleistocene	1.8	Modern humans appear. Four major glaciations cause rapid shifts in ecological communities.
		Tertiary	Neogene	Pliocene	5	Extensive radiation of flowering plants and mammals. First hominids appear.
				Miocene	23	Coevolution of insects and flowering plants. Dogs and bears appear.
			Paleogene	Oligocene	38	Worldwide tropical rainforests. Pigs, cats, and rhinos appear. Dominence of snails and bivalves in the oceans.
				Eocene	54	Early mammals abundant. Rodents, primitive whales and grasses appear.
				Paleocene	65	Early placental mammals appear; first primates; modern birds.
	M E S O Z O I C	Cretaceous			146	Marsupials, ants, bees, butterflies, flowering plants appear. Mass extinction of most large animals and many plants.
		Jurassic			208	Dinosaurs and gymnosperms dominate the land; feathered dinosaurs and birds appear. Radiation of marine reptiles.
		Triassic			245	Origin of mammals, dinosaurs and true flies. Less diverse marine fauna.
	P A L E O Z O I C	Permian			286	Gymnosperms, amphibians dominant. Beetles, stoneflies appear. Major extinction of 95% of marine species and 50% of all animal families.
		Carboniferous		Pennsylvanian	325	First reptiles, cockroaches and mayflies appear. Extensive coal swamp forests. Sponge reefs.
				Missippian	360	Echinoderms, bryozoans dominant in oceans. Early winged insects. First coal swamp forests.
		Devonian			410	First amphibians. Extensive radiation of fish, land plants. Many corals, brachiopods and echinoderms.
		Silurian			440	First spiders, scorpions, centipedes, early insects, vascular plants, jawed fish and large reefs appear.
		Ordovician			505	First land plants, primitive fungi, sea weed appear. Diverse marine life: corals, molluscs, bivalves, echinoderms, etc.
		Cambrian			543	Rise of all major animal groups. Metazoan life abundant; trilobites dominant. First fish. No known terrestrial life.
PROTEROZOIC EON					570	Origin of multicelled organisms. First sponges, colonial algae and soft-bodied invertebrates.
ARCHEAN EON					2,500	Oxygen levels rise as a result of photosynthetic organisms. First eukaryotes (single-celled algae): 1.4 billion years old. Earliest life, anaerobic prokaryotes (bacteria, archaeans) originate 3.5 billion years ago.
HADEAN EON					3,800-4,600	No life known. Cooling and solidifying of Earth's crust.

Links:

Radiometric Dating Bill Nye Discoveries Video

Gizmo Half-Life

KT Boundary Discovery Video

Radioactivity

Index Fossils