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Geologic Time Scale. Rocks and fossils tell us about our world’s past. Each ring represents a year. Width of the ring tells us how much the tree grew that year. Thick rings mean enough water for good growth. Helps develop weather patterns. Tree Rings. Greenland and Antarctica
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Each ring represents a year. • Width of the ring tells us how much the tree grew that year. • Thick rings mean enough water for good growth. • Helps develop weather patterns Tree Rings
Greenland and Antarctica • Snow has built up massive layers of ice • Scientists drill a hole in the ice and take out a tube of ice • This shows a vertical timeline of Earth’s past. Ice Cores
Scientists analyze the trapped air to see how the atmosphere has changed. • Dust or ash trapped show when volcanic activity. • Different levels of ice show temperature differences. Ice Cores
Fossils should be arranged in order for things to make sense • Shows the age in relation to other things. • There are many things that cannot be given exact ages. Relative Aging
The older the rocks, the further down they are. • Things found in the layers show us how old they are. • Movement of plates can disturb the layers. • Compare disturbed and undisturbed layers.
Sedimentary rock can be disturbed by igneous rock. • How? • Magma pushes up through the sedimentary rock. Igneous Rock
If the molten rock erupts, if forms a new layer. • The igneous rock is younger than the sedimentary rocks under it, but older than the sedimentary rocks above.
The actual age of something is called its absolute age. • Atoms breakdown or change into other elements. • That breakdown is called radioactivity. Radioactive Dating
The radioactivity is important because the atom will breakdown at the same rate forever. • Half-life is the amount of time it takes for half of atoms in a sample to change. • Some are fractions of a second, some are billions of years.
Geologic time scale divides Earth’s history into parts based on major events.
Eon • Largest unit of time • Earth’s 4.6billion year history has 4 eons. Divisions of Geologic Time
Era • Eons are divided into eras. • Most recent eon has three eras • Paleozoic • Mesozoic,and • Cenozoic
Period • Each era is divided into periods
Epoch • The periods of the Cenozoic, the most recent era are further divided into epochs
The first three Eons are called Precambrian time and make up approximately 90% of Earth’s history. • Any fossils from this time are too small to be viewed without a microscope.
The most recent eon • Began 544 mya • Divided into three eras: • Paleozoic • Mesozoic • Cenozoic Phanerozoic Eon
All life was in the ocean • Fish, the first life with a backbone developed during this time. • Towards the end of the era, life moved on to land. • Reptiles, insects and ferns were common. • A mass extinction occurred at the end of the era. Paleozoic Era
Lasts for 183 my • Best known for the dinosaurs • Mammals, birds and plants also appeared. • For some of this time, North America was covered in a sea. • Another mass extinction occurs at the end of the era. • Possible cause was a massive asteroid. Mesozoic Era
Quarternary • 2mya to the present • A series of ice ages • Mammoths, saber toothed cats, other giant mammals • Fossils of first humans found. Dated to 100,000 years ago. • Ocean levels rose and fell. Allowed humans to travel. Cenozoic Era “Age of Mammals”
Started 65 mya • Often called the “Age of Mammals” • Divided into two periods; Tertiary/Quarternary Cenozoic Era
