About (1) __________, the earth was formed as the solar system came into

existence with the other planets rotating around the sun. (2) __________ is said to be

geologically violent because of the continuous bombardment by meteorites and

volcanic eruptions. With this condition, minerals were formed from the elements and

compounds contained in the molten material. The oldest material found on earth is

the (3) __________ that is estimated to be 4.3 billion years old. Life on earth is believed

to begin 3.5 billion years ago with single –celled prokaryotes, as discovered in

sedimentary rock formations called (4) __________. As early as (5) __________, the first

photosynthetic organism thrived the earth which is blue green algae called

cyanobacteria. It was 2.0 billion years ago when the first eukaryotes appeared and

the influx of multicellular organisms occurred 1.2 billion years ago. During the

Paleozoic Era which lasted 542 to 251 MYA, the Cambrian and Ordovician Period

has been known as the age of invertebrates when trilobites and cephalopods became

dominant in the (6) __________. The (7) __________ is the age of reptiles that has a

span of 251 to 65.5 MYA divided into Triassic, Jurassic and Cretaneous Period. (8)

__________ is the era of recent life and based on paleontological evidence (9) __________

have evolved 250 thousand years ago. (10__________ are the only surviving species

and one of the living evidences that life have existed on earth.