Page 10 - The Dinosaur Book and Other Wonders of the Prehistoric World (DK-Smithsonian)

Timeline

Introduction of life

The story of life on Earth is written in the rocks. Over millions of Early Earth KEY
years, sediments like sand and clay settle on the floors of lakes Paleozoic Era
and oceans and harden to form layer after layer of sedimentary
rock. Trapped in these ancient deposits are the fossilized Mesozoic Era
remains of prehistoric organisms, with each layer capturing Cenozoic Era

a snapshot of life from a different period in history. Million years ago MYA

251–200 MYA 200–145 MYA

Triassic Jurassic
Reptiles ruled the world in The Jurassic saw the rise
the Triassic. They gave rise of the colossal plant-eating
to the first dinosaurs, the Rhamphorhynchus sauropod dinosaurs such as
first flying reptiles, and Brachiosaurus, as well as the
the first true mammals, giant meat-eating theropods
which were little bigger that preyed on them. Smaller
than shrews. Crocodiles theropods evolved into the first
and turtles appeared, and birds. Deserts shrank and forests
the giant aquatic reptiles of conifer trees, monkey puzzles,
cruised the ocean. and ferns spread across the land. Allosaurus

299–251 MYA
Permian
Moschops Earth’s climate dried out in the Permian, and
deserts replaced forests. Reptiles and related
animals called synapsids were the dominant land
animals. Unlike amphibians, which breed in water,
reptiles laid waterproof eggs and could breed on
land. At the end of the Permian, most of
Earth’s species were wiped out by
a catastrophe of
Edaphosaurus unknown cause.

4.6–0.5 billion years ago 542–488 MYA

Precambrian Cambrian
The Precambrian is a supereon A wide range of new animal fossils
that makes up nearly nine-tenths appear in rocks from the Cambrian
of Earth’s history. For most of it, the Period. A sudden burst of evolution—
only life forms were single-celled the Cambrian explosion—seems to
organisms in the ocean, such as have produced animals with the first
cyanobacteria. Fossilized imprints limbs, heads, sense organs, shells, and
of much larger, leaf-shaped exoskeletons. All the major categories
organisms that might have been of invertebrate alive today originated
animals appeared about 600 million in the Cambrian, from mollusks and
years ago. Known as the Ediacaran arthropods to echinoderms such as
organisms, these life forms vanished Helicoplacus (a relative of starfish).
at the end of the Precambrian.
8 Cyanobacteria Helicoplacus

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