Quiquqiquqiqizz Flashcards
(20 cards)
It is a chronological framework
used to organize Earth’s history, spanning 4.6 billion
years. It is divided into Eons, Eras, Periods, and Epochs.
Each division highlights critical geological, climatic, and
biological milestones, including the evolution of life
and mass extinction events.
Geologic Time Scale
Formation of Earth (~4.6 billion years ago)
from a cloud of gas and dust.
Hadean Eon
Known as the “Age of Ancient Life.”
Spans six periods, beginning with the rapid
diversification of life and ending with the
largest mass extinction.
Paleozoic Era (541–252 million years ago)
Known as the “Eon of Visible Life.”
Life diversified significantly, and complex
ecosystems emerged.
Divided into three Eras: Paleozoic, Mesozoic, and Cenozoic.
Phanerozoic Eon (541 million years ago–Present)
Marks the lead-up to the “Cambrian Explosion” of life in the next eon.
Great Oxygenation Event (~2.4 billion years ago): Oxygen levels increased in the atmosphere due to cyanobacteria.
Emergence of the first eukaryotes (cells with nuclei and organelles).
Proterozoic Eon (2.5 billion–541 million years ago)
Cambrian Explosion: Rapid increase in
biodiversity; most animal phyla (e.g.,
arthropods, mollusks, echinoderms) appeared.
Early marine ecosystems dominated by
trilobites and brachiopods.
First chordates (ancestors of vertebrates)
appeared.
First jawless fish at the end of the Cambrian period
No life on land; all organisms were marine.
Cambrian Period (541–485 million years ago)
Cold climate
First corals
Marine algae and sponges appeared
First jawless fish evolved into early vertebrates,
becoming armored fish
Plants began colonizing land (non-vascular
plants like mosses).
Major glaciation and sea-level drop caused the
Ordovician-Silurian Extinction, wiping out ~85%
of species.
Ordovician Period (485–443 million years ago)
Known as the “Age of Fishes.”
Key Events:
Sea level was high
Jawed fishes, sharks, and lobe-finned fishes
(ancestors of tetrapods) diversified.
First forests, ferns and seed-bearing plants
appeared, no flowering plants yet
First tetrapods (proto-amphibians) emerged.
Trilobites are declining.
Ended with the Late Devonian Extinction, likely
due to oxygen depletion in oceans (~75% of
species lost).
Devonian Period (419–359 million years ago)
Events:
Vascular plants evolved, enabling plants to grow taller.
Early terrestrial arthropods (millipedes, arachnids) colonized land.
Coral reefs expanded.
Jawless fish evolved into jawed fish
Silurian Period (443–419 million years ago)
Pangaea is moving.
Known as the “Age of Reptiles.”
Dinosaurs, mammals, and birds evolved.
Mesozoic Era (252–66 million years ago)
Key Events:
Ideal time for dinosaurs.
Dinosaurs like Stegosaurus and Brachiosaurus
thrived.
First birds (e.g., Archaeopteryx) appeared, due
to evolution of insectivores.
Theropod Dinosaur Hypothesis.
Oceans were dominated by ichthyosaurs and
plesiosaurs.
Small burrowing mammals underground.
Conifers continue to flourish (“Age of Cycads”).
Jurassic Period (201–145 million years ago)
Key Events:
Flowering plants (angiosperms) evolved and
spread.
Insect diversification.
Tyrannosaurus rex and Triceratops lived during
this time.
Small birds and mammals also diversify.
Ended with the Cretaceous-Paleogene
Extinction (K-Pg) (~75% of species lost, caused by an asteroid impact forming the Chicxulub Crater).
Cretaceous Period (145–66 million years ago)
Dry climate.
Formation of the supercontinent Pangaea.
Early mammal-like reptiles (therapsids) and the
first gymnosperms (conifers).
Reptiles started to diversify.
Trilobites were completely wiped out
Ended with the Permian-Triassic Extinction (The
Great Dying), the largest mass extinction (~96%
of species lost).
Permian Period (299–252 million years ago)
Key Events:
Recovery from the Permian extinction.
First dinosaurs and mammals appeared.
Mammals were competing with reptile but still
overwhelmed.
Crocodiles were abundant.
Evolution of insects from incomplete
metamorphosis into complete metamorphosis.
Ended with the Triassic-Jurassic Extinction
(~76% of species lost, possibly due to volcanic activity).
Triassic Period (252–201 million years ago)
Known as the “Age of Mammals.”
Life diversified into forms recognizable today.
Cenozoic Era (66 million years ago–Present)
Key Events:
Mammals diversified after the extinction of
dinosaurs.
Grasslands expanded, ruminants diversify.
Primates evolved.
Paleogene Period (66–23 million years ago)
Early humans (genus Homo) evolved.
Climate cooled, leading to Ice Age.
Neogene Period (23–2.6 million years ago)
Warm and humid climate, with no polar ice
caps.
Recovery of ecosystems after the asteroid
impact.
Mammals diversified and increased in size,
filling ecological niches left by extinct
dinosaurs.
First primitive primates appeared.
Flowering plants (angiosperms) continued to
dominate; the first modern rainforests began
forming.
First cactus and palm trees.
Early birds diversified.
Paleocene Epoch (66–56 million years ago)
It represents the post-Ice Age
period, characterized by the rise of human
civilization and the development of the
modern world.
Holocene Epoch (11,700 years ago–Present)
Known as the Ice Age, characterized by
repeated glaciations and human evolution.
Pleistocene Epoch (2.6 million–11,700 years ago)
