Biology (Holt)

Formation of the Basic

Chemicals of Life

Most scientists think that life on Earth developed through natural
chemical and physical processes. It is thought that the path to the
development of living things began when molecules of nonliving
matter reacted chemically during the first billion years of Earth’s
history. These chemical reactions produced many different simple,
organic molecules. Energized by the sun and volcanic heat, these
simple, organic molecules formed more-complex molecules that
eventually became the building blocks of the first cells. The hypoth-
esis that many of the organic molecules necessary for life can be
made from molecules of nonliving matter has been tested and sup-
ported by results of laboratory experiments.

1 How Did Life Begin?

Modeling Radioactive Decay

You can use some dried corn, a box, and a watch to

make a model of radioactive decay that will show

you how scientists measure the age of objects.

Materials

approximately 100 dry corn kernels per group, cardboard box,

clock or watch with a second hand

Procedure

1.On a separate sheet of

paper, make a data table like

the one below.

2.Assign one member of your

team to keep time.

3.Place 100 dry corn kernels

into a box.

4.Shake the box gently from

side to side for 10 seconds.

5.Keep the box still and

remove and count the

kernels that “point” to the

left side of the box, as shown

below. Record in your data

table the number of kernels

you removed.

6.Repeat steps 4 and 5 until all

kernels have been counted

and removed.

7.Calculate the number of

kernels remaining for each

time interval.

8.Make a graph using your

group’s data. Plot “Total

shake time (seconds)” on

the x-axis. Plot “Number

of kernels remaining” on the

y-axis.

Analysis

1. Identifywhat the removed
   kernels represent in each step.


2. Calculatethe half-life of
   your sample, in seconds, that
   is represented in this activity.


3. Calculatethe age of your
   sample, in years, if each
   10-second interval represents
   5,700 years.


4. Evaluatethe ability of this
   model to demonstrate
   radioactive decay.

Total shake time Number of kernels Number of kernels

(seconds) removed remaining

10

20

30

http://www.scilinks.org

Topic: Radioactive Decay

Keyword: HX4154

2B 2C 3E