a view of earth’s past earth and space science austin high school 2015-2016
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Geological Time Earth’s surface is constantly changing
As conditions change, organisms flourish an than later become extinct
Evidence of change is recorded in the rock layers of earth’s crust
To describe the sequence and length of change, scientist have developed a geologic time scale
The scale outlines the development of earth ad life on earth
The Geological ColumnApplying the principle that old layers of rock are below young
layers scientist determine the relative ages of sedimentary rock in different areas around the world
No single area on earth contain a record of all geologic time, scientist combined their observations to create a standard arrangement of rock layers
The Geological ColumnOrdered arrangement of rock layers is called a geologic
column
Geologic column represent a timeline of the earth’s history
Oldest rock at the bottom of the column
Columns are distinguished by the rock type and kinds of fossils the layers contain
Fossils in upper layers layers resemble modern plants/animals, where lower (older) layers fossils differ from those living today
The fossils discovered in old layers are from species that have been extinct for millions of years.
Using a Geologic ColumnGeological columns were first developed using factors such
as average rates of sediment deposition to estimate the age of rock layers
Development of radiometric dating (ex. Carbon dating) to determine the absolute ages of rock layers with more accuracy
Geologic columns can now be used to estimate the age of rock that cannot be dated radiometrically
A comparison between a given rock layer and a similar layer in a geologic column (contains same fossils or same relative position) can be used to determine age
Division of Geologic TimeGeological history of earth is marked by major change in
earth’s surface, climate, and types of organisms
Geologist use these indicators to divided the geologic time scale into smaller units
Geological time is generally characterized by fossils of a dominant life-form.
Scientist commonly use abbreviations when they discuss geologic time (so long) Ma = mega annum, which means “one million years”
Eons and ErasLargest unit of geologic time is an eon
Geologic time is divided into four eonsThe Hadean eonThe Archean eonThe Proterozoic EonThe Phanerozoic Eon
The first three eons are part of a time internal commonly known as Precambrian time
Precambrian is a 4 billion year interval that contains most of earth’s history
Very few fossils exist in early Precambrian rocks, so dividing Precambrian time into smaller time units is difficult
Precambrian
Eons and ErasAfter Precambrian time the Phanerozoic eon began
This eon is divided into smaller units of geologic time called eras
The first era of the Phanerozic eon was the Paleozoic Era which lasted 291 millions years
Paleozoic rocks contain fossils of wide variety of marine and terrestrial life forms
The Mesozoic Era Began after and lasted 186 million years
Mesozoic fossils include early forms of birds and reptiles
The present geologic era is the Cenozoic Era which began 65 million years ago.
Fossils of mammals are common in Cenozoic Rocks
Period and EpochsEras are divided into shorter time units called periods
Each period is characterized by specific fossils and are usually named for the location in which the fossils were first discovered
Where rock records are most complete and least deformed, ad detailed fossils record may allow scientist to divide periods into shorter time units called epochs
Epoch may be divided into smaller units of time called ages which are defined by the occurrence of distinct fossils in the fossil records
EvolutionFossils indicate the kinds of organisms that lived when rock
formed
By examining rock layers and fossils scientist have discovered evidence that species of living things have changed overtime, process called evolution
Evolution is the gradual development of new organisms from preexisting organisms
Evidence for evolution includes the similarity in skeletal structures of animals
Theory of evolution by natural selection was proposed by 1859 by Charles Darwin
Evolution and Geologic ChangeGeologic and climate change can affect the ability of some
organisms to survive
Using geologic evidence, scientists try to determine how environmental changes affected organisms in the past
Fossils records show that some organisms survived environmental changes while other organisms disappeared
Fossils are used to learn why some organisms survived long periods of time without changing while other organisms changed or became extinct
Precambrian TimeEarth was formed about 4.6 billion ears ago as a large cloud or
nebula spun around the newly formed sun
Material spun around the sun, particles of matter began to clump together and eventually formed earth and the other planets of the solar systems
The time interval that began with the formation of Earth and ended about 542 million years ago called known as Precambrian time.
This division of geologic time makes up about 88% of Earth’s history
Relatively little is known about what happened during this time
Information is lacking because rock record is difficult to interpret
Precambrian are so severely deformed and altered by tectonic activity that the original order of the rock layer is rarely identifiable
Precambrian RocksLarge areas of exposed Precambrian rocks, called shields
exist on every continent
Shields are a result of several hundred millions years of volcanic activity, mountain building, sedimentation, and metamorphism
Precambrian shield were lifted and exposed at earth’s surface
Half of the valuable minerals deposits in the world occur in rocks of Precambrian shields
Valuable minerals include nickel, iron, gold, and copper
Precambrian LifeFossils are rare in Precambrian rocks because life-forms lack
bones, shells, or other hard parts that commonly form fossils
Precambrian rocks are old, nearly 3.9 billion years
Volcanic activity, erosion, and extensive crustal movements probably destroyed most of the fossils that may have formed
The most common Precambrian fossil are Stromatolites
Stromatolites are reef like deposits formed by blue-green algae
Stromatolites indicate tha shallow seas covered much of Earth during periods in Precambrian time
Imprints of worms, jellyfish, and single-celled organisms have also been discovered from late Precambrian time
The Paleozoic Era• Cambrian Period• Ordovician Period• Silurian Period• Devonian Period• Carboniferous Period• Permian Period
The Paleozoic EraGeological Era that began 542 million years ago and ended
about 251 million years ago
At the beginning of this era, Earth’s landmasses were scattered around the world
By the end, landmasses had collided to form the super-continent Pangaea
Tectonic activity created new mountain ranges and lifted large area of land above sea level
Paleozoic rocks hold an abundant fossils records
# of plant and animal species on earth increased dramatically at the beginning of this Era
The Cambrain PeriodVariety of marine life-form appeared during this periods
life-forms were more advanced than previous life-forms and quickly displaced the primitive organisms as the dominant life-forms
Marine invertebrates, animals that do not have backbones, thrived in the warm waters
Most common invertebrates were trilobites
2nd most common animal, brachiopods, a group of shelled animals
Other common Cambrian invertebrates included worms, jellyfish, snails, and sponges
No evidence of land-dwelling plants or animals discovered
The Ordovician PeriodDuring this period trilobites began to shrink
Clamlike, Brachiopods and cephalopods became dominant invertebrates life-forms
Large # of corals appeared
Vertebrates, animals that have backbones, had appeared
Most primitive vertebrates were fish
Ordovician fish did not have jaw or teeth and their bodies were covered with thick, bony plates
No plant life on land
The Silurian PeriodVertebrate and invertebrate marine life continued to thrive
Echinoderm (relatives to modern sea stars) and corals became more common
Eurypterids, Scorpion-like sea creatures existed during this period
Fossils of giant of these creatures nearly 3 meters long were discovered in western New York
Near the end of period, earliest plant and animals evolved on land
The Devonian PeriodCalled the Age of Fishes
Many fossils of bony fishes were discovered in rocks
Lungfish, were fish that has the ability to breathe air
Fist amphibians evolved, resembled huge salamanders
During this periods, land plants began to develop
In the sea, brachiopods and mollusk continued to thrive
The Carboniferous PeriodClimate was generally warm and high humidity
Forest and swamps covered much land
Amphibians and fish continued to flourish
Insects, giant cockroaches and dragonflies were common
This period is divided into two periods: Mississippian and Pennsylvanian
Vertebrates that were adapted to life on land appeared, these early reptiles resembled large lizards
The Permian PeriodPermian period marks end of Paleozoic Era
A mass extinction of large number of Paleozoic life-forms occurred
Collision of tectonic plates created the Appalachian Mountains
Shallow inland seas that had covered much of earth disappeared
As sea retreated, many species of marine invertebrates became extinct
Reptiles and amphibians survived the environmental changes and dominated Earth in the million years that followed
End of Permian, 90% of marine organism and more than 70% of land organisms died
The Mesozoic Era Geological era began about 251 million years ago and ended
about 65 million years ago
Earth’s surface changed dramatically, Pangaea broke into smaller continents and tectonic plated drifted and collided
Collision uplifted mountain ranges such as the Sierra Nevada in California and Andes in South America
Shallow seas and marshes covered much of the land
Climate was warm and humid
Lizards, turtles, crocodiles, snakes, and variety of dinosaurs flourished
Also known as the “Age of Reptiles”
This Era has rich fossil records and is divided into three periods
The Triassic PeriodDinosaurs appeared during this period
Some dinosaurs were the size of squirrels and some weighed as much as 15 tons
Forest were lush with cone-bearing trees and cycads which are plants that resemble the palm trees of today
Reptiles called ichthyosaurs lived in the Triassic oceans
During this time the first mammals, small rodent-like forest dwellers appeared
The Jurassic PeriodDinosaurs became the dominant life-form
Fossils indicate two major groups of dinosaurs evolvedSaurischians = “lizard-hipped”
Included herbivores (plant eaters) and carnivores (meat eaters)Ornithischians = “bird-hipped”
Flying reptiles called pterosaurs were common during this period
The Cretaceous PeriodDinosaurs continued to dominate
Tyrannosaurus rex existed during this time
Other dinsosaur included ankylosaurs, ceratopsians, hadrossaurs
Plant life become very sophisticated
Earliest flowering plants or angiosperms appeared
Most common of these plants included trees (magnolias and willows),
Dinosaurs became extinct
The Cenozoic EraDivision of time that began 65 million years ago and
includes the present time
Continents moved to their present-day positions
Plated collided to form Alps and Himalayas Mountain ranges
Dramatic change in climate occurred
Mammals became the dominant life-form and underwent many changes
“Age of the Mammals”
Cenozoic EraDivided into 2 periods:
Tertiary period - First primates appear and flowering plants become the most common.
Quaternary period - Humans evolve and large mammals like woolly mammoths become extinct.
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