Geologic Time Scale Flashcards
the change in the characteristics of a species over several generations; simply put, it is change over time
evolution
author of “On the Origin of Species”, developed the theory of natural selection
Charles Darwin
refers to the process where over long periods of time, helpful variations can appear in a species, while “unfavorable” ones disappear
natural selection
divides up the history of the earth based on life forms that have existed during specific times
geological time scale
a unit or division of geological time
geochronological units
the longest subdivision; based on the abundance of certain fossils
eons
second largest subdivision; marked by the major changes in the fossil record
eras
based on the types of life existing at the time
periods
shortest subdivision; marked by differences in life forms and can vary from continent to continent
epochs
a method used to determine the age of an object based on the known decay rate of radioactive isotopes
radiometric dating
determines the order of past events without necessarily determining the age of objects
relative dating
also known as radiocarbon dating, a type of radiometric dating that determines the age of an organic material by measuring the radioactivity of its carbon content
carbon dating
the time on earth when it is still forming so no fossils or records or life are found in this eon
Hadean Eon
starts when the earth started to cool down, cyanobacteria started to thrive
Archean Eon (archea = ancient)
around this time, photosynthetic bacteria spewed tons of oxygen into the atmosphere which gave rise to the first complex life forms (Charnia and Dickinsonia)
Proterozoic Eon
it means current; the now
Phanerozoic Eon
The Hadean, Archean, and Proterozoic Eon make up the _______ Eon.
Precambrian Eon
is the oldest era, the early life forms thrived in water
Paleozoic Era
explosion of life, life starts in water, marine invertebrates (trilobites and brachiopods) were dominant, supercontinent Gondwana forms near the South Pole (present-day Florida)
Cambrian
1st animals with bones appeared, a very cold time on earth; the first mass extinction happened due to the ice caps in present-day Africa, Gondwana, Baltica, Siberia, and Laurentia were the four main continents
Ordovician
first land plants and animals appeared, Laurentia collides with Baltica and closes the lapetus Sea, first millipede fossils and sea scorpions were found in this period
Silurian
age of the fish, pre-Pangea forms, present-day Arctic Canada was at the equator and hardwoods began to grow; amphibians, evergreens, and ferns appear
Devonian
first seed plants appeared, North America is covered by shallow seas; bryzoa, brachiopods, and blastoids flourished
Mississippian
modern North America begins to form, ice covers the Southern hemisphere and coal swamps formed along the equator; lizard and winged insects first appeared
Pennsylvanian
marks the last period of the Paleozoic, Pangea forms, the Appalachian mountain range rises, the deadliest mass extinction called the “Permian-Triassic Extinction” occurred that wiped out 95% of life on Earth
Permian
dinosaurs dominated this era, ______ means ‘middle life’
Mesozoic Era
first dinosaurs appeared; first mammals (small rodents) appeared; after the mass extinction, life and fauna needed to re-diversify; rocky mountains formed; first turtle fossils were found from this period; Pangea breaks apart
Triassic
Pangea was still breaking apart; the “Golden age of dinosaurs”; the first birds appeared; North America continued to shift away from Africa
Jurassic
T-Rex flourished; first snakes and primates appeared; first flowering plants; deciduous trees; the 5th mass extinction (Cretaceous-Paleogene extinction) caused all the dinosaurs to be extinct
Cretaceous
the earth’s current geological era, also known as the “age of the mammals”
Cenozoic Era
first horses appeared and tropical plants dominated the land
Paleocene (under tertiary)
grasses spread and large mammals thrived
Eocene (under tertiary)
dogs, cats, and apes appeared
Oligocene (under tertiary)
horses, mastodons, camels, and tigers roamed free
Miocene (under tertiary)
hominids developed and the Grand Canyon was formed
Pliocene (under tertiary)
modern humans developed; the last ice age happened
Pleistocene (under quaternary)
humans flourish; one that we are currently living in
Holocene (under quaternary)
