Geologic Time Scale Flashcards
the “calendar” for events in Earth history. It subdivides all time into named units of abstract time called—in descending order of duration—eons, eras, periods, epochs, and ages.
- chronological, relates rock and fossils
geologic time scale
time span of all 4 eons on earth
4.6 billion years
eons on earth
hadean, archaean, proterozoic, phanerozoic
informal division of Precambrian time occurring between about 4.6 billion and about 4.0 billion years ago. This Eon is characterized by Earth’s initial formation—from the accretion of dust and gases and the frequent collisions of larger planetesimals—and by the stabilization of its core and crust and the development of its atmosphere and oceans.
- enormous amounts of heat that likely prevented much of the rock from solidifying at the surface (hellish)
- calmed later on leading to the presence of carbohydrates, protein, lipids, and nucleic acid (due to meteors?)
hadean eon
Eon
(4-2.5 billion years ago) methane droplets in the air shrouded the young Earth in a global haze. There was no oxygen gas on Earth. Oxygen was only in compounds such as water. Complex chemical reactions in the young oceans transformed carbon-containing molecules into simple, living cells that did not need oxygen to live. (Extremophiles, Archaean - those that thrived in harsh environments) Instead, they made energy out of sulfur and other elements.
- the rise of the 1st living things - archaea bacteria (prokaryotes)
- presence of cyanobacteria - They made gaseous, or free, oxygen from carbon dioxide, water, and sunlight—the process called photosynthesis. As cyanobacteria created more free oxygen, the amount of oxygen in the atmosphere reached one percent of today’s level, which is 21 percent
archaean eon
eon (prototypes of life)
the younger of the two divisions of Precambrian time
- extended from 2.5 billion to 541 million years ago
- the atmosphere and oceans changed significantly.
- the fossil remains of bacteria and blue-green algae as well as the first oxygen-dependent animals, the Ediacara fauna.
- hosting the transition to an oxygenated atmosphere.
- the Great Oxygen Event, Snowball Earth, formation of the supercontinent Rodinia, and the evolution of eukaryotic cells and of multicellular organisms (bc of oxygenated atmosphere).
proterozoic eon
occurred when cyanobacteria living in the oceans started producing oxygen through photosynthesis. As oxygen built up in the atmosphere anaerobic bacteria were killed leading to the Earth’s first mass extinction
the great oxygen event
What possibly caused the snowball earth during proterozoic era
decline in the CO2 level (probably bc of cyanobactera), reduced concentration of greenhouse gases, such as methane and/or carbon dioxide, perturbations of Earth’s orbit, etc.
or
Possibly by a lowering of atmospheric greenhouse gases to near-present levels through tectonically-mediated rock weathering, when the Sun was considerably dimmer than present.
defined as the supercontinent that existed in early Neoproterozoic time
rodinia
The name means: “before the Cambrian period.” This old, but still common term was originally used to refer to the whole period of earth’s history before the formation of the oldest rocks with recognizable fossils in them.
- covers almost 90% of the entire history of the Earth. It has been divided into three eons: the Hadean, the Archean and the Proterozoic.
- only microfossils?
pre-cambrian era
the eon of visible life
- evident life
- the current geologic eon in the geologic time scale, and the one during which abundant animal and plant life has existed. It covers 538.8 million years to the present
phanerozoic eon
eras under phanerozoic eon
paleozoic, mesozoic, cenozoic
era under phanerozoic eon
major interval of geologic time that began 541 million years ago with the Cambrian explosion and ended about 252 million years ago with the end-Permian extinction, the greatest extinction event in Earth history.
- the time when pangaea was formed
- takes its name from the Greek word for ancient life.
- began with the breakup of one supercontinent and the formation of another. Plants became widespread. And the first vertebrate animals colonized land
paleozoic era
periods under paleozoic era
cambrian, ordovician, silurian, devonian, carboniferous, permian
period under paleozoic era
part of the Paleozoic era, produced the most intense burst of evolution ever known.
- earliest time division of the Paleozoic Era, extending from 541 million to 485.4 million years ago.
- land plants had not yet evolved, so the terrestrial world was devoid of vegetation. However, in the oceans (underwater) many marine invertebrates, including sponges and brachiopods (lamp shells),
- ended by an extinction event (mostly invertibrates)
cambrian period
the unparalleled emergence of organisms between 541 million and approximately 530 million years ago at the beginning of the Cambrian Period. The event was characterized by the appearance of many of the major phyla (between 20 and 35) that make up modern animal life.
- an extraordinary diversification of marine animals,
Cambrian explosion
the second period of the Paleozoic Era. It began 485.4 million years ago, following the Cambrian Period, and ended 443.8 million years ago.
- This is best known for its diverse marine invertebrates, including graptolites, trilobites, brachiopods, and conodonts (early vertebrates). More recently, tetrahedral spores that are similar to those of primitive land plants have been found, suggesting that plants invaded the land at this time.
- when invertebrates evolved, and vertebrates emerged from underwater
- jawless fish
- ended by the 1st extinction event in phanerozoic era
Ordovician period
The extinction was a most likely a result of global cooling and reduced sea levels, which dramatically impacted the many marine species living in warm, shallow coastal waters. (probably due to the depletion of C02, too many plants)
the first of the “big five” major mass extinction events in Earth’s history,
- A major ice age is known to have occurred in the southern hemisphere and climates cooled worldwide.
- those that survived underwater adapted to walk
ordovician-silurian extinction
period under paleozoic era
the third period of the Paleozoic Era. It began 443.8 million years ago and ended 419.2 million years ago
- first land plants, insects, and jawed fish
Silurian period
period under paleozoic era
an interval of the Paleozoic Era that follows the Silurian Period and precedes the Carboniferous Period, spanning between about 419.2 million and 358.9 million years ago.
- age of fishes
- Late in the period the first four-legged amphibians appeared, indicating the colonization of land by vertebrates.
- first land animals
- ended with an extinction event
- cartilagenous fishes
devonian period
A second mass extinction
- primarily affected the marine community
- dissolved oxygen in oceans decreased (bc kumonti autotrophs), prohibiting decay and allowing the preservation of organic matter, which then over time underwent through anaerobic respiration and became oil
late devonian extinction event
period under paleozoic era
- is a geologic period and system of the Paleozoic that spans 60 million years from the end of the Devonian Period 358.9 million years ago (Mya), to the beginning of the Permian Period, 298.9 million years ago.
- “coal bearing”
- when moss and swamps underwent decomposition anaerobically, overtime turning into coal
- takes its name from large underground coal deposits that date to it.
- pangaea is forming
- first reptiles and large cartilaginous fishes appear
- evolution of lungs?
- age of amphibians?
carboniferous period
period under paleozoic era
the last period of the Paleozoic Era. began 298.9 million years ago and ended 252.2 million years ago, extending from the close of the Carboniferous Period to the outset of the Triassic Period.
- Earth’s crustal plates formed a single, massive continent called Pangaea.
- reptiles replaced amphibians in abundance, but is also the age of amphibians
- ended with the greatest extinction event
permian period
colloquially as the Great Dying, formed the boundary between the Permian and Triassic geologic periods, and with them the Paleozoic and Mesozoic eras respectively, approximately 251.9 million years ago. It is the Earth’s most severe known extinction event,with the extinction of 57% of biological families, 83% of genera, 81% of marine species and 70% of terrestrial vertebrate species. It was the largest known mass extinction of insects. (due to volcanic activity and high levels of CO2 - climate change)
- about 90% of species were wiped out
permian-triassic extinction event
