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Earth Science. November 12, 2005 Dr. Clodfelter. Geologic Time Scale. The Geologic Time Scale. The history of the Earth is broken up into a hierarchical set of divisions for describing geologic time. The Geologic Time Scale, cont.
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Earth Science November 12, 2005 Dr. Clodfelter
The Geologic Time Scale The history of the Earth is broken up into a hierarchical set of divisions for describing geologic time
The Geologic Time Scale, cont. Highlights of recent fossil finds from throughout geologic time (from most ancient to most recent) are: • Precambrian Era: the first fossil bacteria, sponges, corals, and algae appear • Cambrian Period: abundant invertebrate fossils such as mollusks, crustaceans
The Geologic Time Scale, cont. • Triassic Period: the first fossils of primitive dinosaurs appear • Jurassic Period: the first fossil mammals and birds; first fossil flowering plants appear • Cretaceous Period: large fossil dinosaurs appear
Precambrian Eon4.5 Billion to 543 Million Years Ago • Nearly 4 thousand million years after the Earth began • The first animals left their traces • Makes up roughly 7/8 of the Earth's history
Archaean Era3.8 to 2.5 Billion Years Ago • The atmosphere was very different from what we breathe today • The Earth's crust cooled enough that rocks and continental plates began to form • Life first appeared on Earth • bacteria microfossils
Phanerozoic Eon543 Million to • Majority of macroscopic organisms, fungal, plant and animals lived • Appearance of animals that evolved external skeletons – like shells – and animals that formed internal skeletons – like vertebrates
Paleozoic Era543 to 248 Million Years Ago • In the beginning, multicelled animals underwent a dramatic "explosion" in diversity • At the end, the largest mass extinction in history wiped out approximately 90% of all marine animal species
Mesozoic Era248 to 65 Million Years Ago • Mesozoic means "middle animals” • Lasted 70 Million Years • Time of transition • The world-continent of Pangaea existed • The time in which life as it now exists on Earth came together • Important today because of the fossils and oil left behind
Mesozoic Era248 to 65 Million Years Ago Divided into three time periods: • the Triassic (245-208 Million Years Ago) • the Jurassic (208-146 Million Years Ago) • the Cretaceous (146-65 Million Years Ago)
Dinosaurs in the Mesozoic Era Dinosaurs... • Evolved in the Triassic Period • Became more diversified in the Jurassic Period • Became extinct in the late Cretaceous Period • Fossils of some of the last dinosaurs to walk the Earth can be found in Montana
Cenozoic Era • The most recent of the three major subdivisions of animal history • The other two are the Paleozoic and the Mesozoic • Spans only about 65 million years • Sometimes called the “Age of Mammals”
A Continental Jigsaw Puzzle: Putting the Pieces Together • 1911 • German meteorologist • Alfred Wegener • theorized that about 300 million years ago all the continents we know today were joined together in a single continent • he named it “Pangaea” (pronounced Pan JEE uh)
A Continental Jigsaw Puzzle: Putting the Pieces Together, cont. • Wegener suggested that Pangaea split apart and its pieces began to “drift,” or move away from each other • He put together his own evidence, as well as others’, to support his Theory of Continental Drift
A Continental Jigsaw Puzzle: Putting the Pieces Together, cont. • At first, Wegener’s ideas were very popular because his evidence seemed quite convincing • Yet a number of observations still remained unexplained • What forces caused the continents to move? • Due to these remaining problems, Wegener’s theory rapidly lost support and continental drift became “just another theory”
What are Crustal Plates? • Earth’s crust isn’t one continuous surface like the skin of an orange • It is made up of gigantic pieces, like pieces of a jigsaw puzzle • Each piece is called a crustalplate • Some plates form the floor of the oceans while other carry the continents
How do the crustal plates move?
Crustal Plates • Molten rock around the Earth’s core heats up the mantle above • Currents of molten rock rise up through the mantle like boiling water • As each current hits the underneath of the crustal plates, it starts to spread out • This slowly pushes or tears the crust apart
Crustal Plates • The plates are always on the move • There are three basic types of plate boundaries • where they are sliding past each other • where plates are separating • where they are converging (approaching each other)
Crustal Plates • Spreading Center - the boundary between separating plates • Usually found in mid-ocean and are marked by rugged mountain chains called mid-ocean ridges • As plates move apart a gap continuously opens between them • Molten rock from the earth’s interior flows into this gap • New crust is continuously formed
Crustal Plates • When plates collide, the force can fold and thrust upward to form mountains • Or the force can push the ocean floor downward to form a deep valley called a trench • Here, molten rock can break through the seabed to form chains of islands like the Hawaiian Islands
Crustal Plate Activity Crustal plate activity can… • Cause earthquakes, volcanic activity, and tsunamis • Earthquakes are signs of the great stresses and which affect the Earth’s crust • Over a million earthquakes occur every year • Tsunamis are giant tidal waves and can travel at 500 mph!
Dinosaur Fossils • Dinosaur Fossil bones have been found in many different parts of the world • Further supports Wegener’s single continent theory • The dinosaurs disappeared suddenly • Different theories as to why • Most widely accepted is the Big Bang Theory
Big Bang Theory • Scientists theorize that a meteor hit the Earth at nearly the speed of light (186,000 miles per second!) • Caused a total black out of the sun • This meteor is believed to have caused the Gulf of Mexico
Earth's Fast Facts • The Earth weighs about 6000 million million million tons • Two-thirds of the earth is covered by water • It would take more than 250 days to walk around the equator • Every year, North America and Europe separate by 3/4ths of an inch • Scientists predict that life on Earth will only last 50 million more years
Earth = Onion • Crust – outermost layer, solid rock, but very thin like skin • Mantle – denser and heavier than the crust, inner part of the mantle is described as “plastic” because it is semi-liquid rock • Core – outer part is made of molten liquid rock that is very dense and heavy, “core” of the core becomes solid and even more dense
Magma • Forms when rocks deep under the Earth’s crust melt • Heat from friction as the rocks rub together can also form magma • In places where the Earth’s crust is weak, magma wells up on the surface as volcanoes or lava flows • As it cools, it becomes solid forming new rock
Rocks • Igneous Rock – formed form cooled magma • Sedimentary Rock – formed by the combining together of broken bits of other rocks or sediments • Metamorphic Rock – changed by extreme pressure or heat
Rocks • Contain complex chemicals called minerals • Kinds of Minerals+ Size of Crystals= how the rock was Formed • Small crystals = rapid cooling • Large crystals = more lengthy cooling
Krakatoa, Indonesia • Volcanic eruption was heard 3,000 miles away • Caused great tidal wave that killed perhaps 36,000 people • Crystals from the magma are smaller because they cooled quickly
Crater Lake, Oregon • The caldera has filled creating one of the deepest lakes • It may erupt again
Sedimentary Rock • Made by the action of water and wind as they laid down like layers of a cake • Pressure increases and they are warmed by the heat from deep in the Earth • Sediment becomes a solid mass of rock
Sandstone Limestone Sedimentary Rock
Decaying Plant Material Peat Coal
How are Fossils Formed? • Sea Creature dies and sinks to the sea bed • The soft body slowly decays creating oil with a layer of gas sitting on top • Skeleton is covered in layers of mud which gradually become solid rock • Sea bed rises above sea level • Erosion moves rock covering fossils so they are now exposed on land
