With a ruler, draw a line that is 20 cm long. Divide the line into five, 4-cm segments. On a scale of each segment representing one billion years, label the following events in the history of Earth: a. formation of the earth
b. origin of life
c. evolution of photosynthesis
d. evolution of eukaryotes
e. evolution of multi-cellular life
f. the Cambrian explosion
g. first vertebrate land animals
h. evolution of dinosaurs
i. evolution of human beings

Solution:

The first traces of the life that existed on the earth can be traced back to about as old as 4.2 billion years. It indicates that life has evolved around 200 million years ago after the first appearance of the liquid water.

The origin of the life on earth is a natural process and is a series of evolution what we see today. Firstly earth was formed by dust and smoke particles and then different forms of life began to evolved on the earth.

The events of the evolution in the history of the earth is shown on the following number line below :

during the process of dna replication, brdu can replace thymidine and incorporate into the newly synthesized dna, cell proliferation thus can be reflected in the extent of brdu incorporation.