• Earth forms from space dust, rocks, and gases.

• It is not a nice place to live. In fact, nothing lives there. © Microsoft Clipart

• First prokaryotes (single-celled organisms with no nucleus) arise.

• They are the ancestors of modern day bacteria and cyanobacteria.

• First single-celled organisms with nuclei (eukaryotes) arise.• They are the ancestors of modern day protists.

• The first soft-bodied invertebrates evolve.• They will evolve into sponges, jellyfish, mollusks,

and worms.• They are the first animals.

• The first hard-bodied invertebrates evolve.• They will become the arthropods (crustaceans, insects, and

arachnids).

• Fish first appear on Earth.• They are very similar in appearance to lampreys

of today• They are the first vertebrates.

• First vascular land plants.• They were fern-like organisms.

• The first amphibious creatures crawl onto land.• They are ancestors of frogs and salamanders.• They breathe through lungs as well as through

the skin.

© G.R. Morton, 1997

• The first true reptiles appear.• They have scales, lungs, and lay eggs with hard,

leathery shells.

© Microsoft Encarta

• The first dinosaurs and the first mammals appear. They are warm-blooded.

• They will lead way to bigger dinosaurs, bigger mammals, and birds.

• Evolution of the first birds.• They are originally dinosaurs with feathers. They

also develop hollow bones to make them lighter.

• The first placental mammals evolve.• They nourish their unborn offspring with

placentas and give birth to live young.• They soon become the dominant mammalian

form on Earth.

• The first human beings appear.• They are almost like us, but not quite, being a

little smaller and a little less upright, and a lot hairier.

• Homo sapiens (us) will not show for another 1.7 million years.

• ClipArt courtesy of Microsoft ClipArt• Amphibian image courtesy of Morton, G.R.

retrieved August 27, 2002 from http://www.glenn.morton.btinternet.co.uk/transit.htm

• All other images © Microsoft Corporation. Microsoft Encarta Encyclopedia 2002.