Download Scientific Investigation and Reasoning Scientific Investigations

Scientific Investigation and Reasoning
Scientific Investigations
Observations
Scientific investigations often begin with observations. An observation is information that you obtain
through your senses, such as sight, sound, and touch.
Hypotheses
Scientific investigations often begin with a problem or questions about an observation. A hypothesis is a
possible explanation for a set of observations or a possible answer to a scientific question. A hypothesis is
often a prediction of what will happen if you introduce a change in a system or process.
For a hypothesis to be valid, it must be testable. This means that you must be able to carry out
investigations and gather evidence that will either support or disprove the hypothesis.
Hypotheses are often based on cause-and-effect relationships and written as "If..then.." statements. For
example, a valid hypothesis could be, "If salt is added to water, then the freezing point of the water will
decrease."
Variables and Controlled Experiments
Investigations are designed to test a hypothesis. All factors that can change in an experiment are called
variables. An experiment in which only one variable is changed at a time is called a controlled
experiment.
The variable that is purposely changed to test a hypothesis is called the manipulated variable.
Manipulated variables are also sometimes called independent variables.
The factor that may change in response to the manipulated variable is called the responding variable.
Responding variables are also sometimes called dependent variables.
Scientists carefully control their variables so they can understand how the variables affect the system as a
whole. This makes the data collected from an experiment meaningful.
However, sometimes scientists collect data that is contradictory or unusual. When this happens, the
scientist should carefully go over the investigation’s design to make sure that there is only one
manipulated variable in the experiment.
Types of Scientific Investigations
Scientific investigations are organized attempts to seek out, describe, explain, and predict natural
phenomena. Scientific investigations are often performed to explore new phenomena, verify the results of
previous investigations, test theoretical predictions, and discriminate between competing theories.
There are many different types of scientific investigations that may be performed. The type of scientific
investigation that is chosen depends on the question that is being asked in the investigation. Also,
scientists sometimes combine aspects of more than one type of investigation.
Different types of investigations include:
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making models
performing a controlled lab experiment
performing a field-based investigation
observing and describing objects, organisms, or events
MAKING MODELS
Making a model of something that is too large, rare, complex, or dangerous to fully observe in person can
help scientists understand how it works.
For example, scientists can use a computer simulation program to predict weather patterns. By entering
past and present weather conditions and phenomena, scientists can collect data from a large span of time
and attempt to predict future weather patterns.
PERFORMING A CONTROLLED LAB EXPERIMENT
If the conditions of an experiment must be very precise, or if an object or organism is not being studied in
its natural setting, it may be beneficial to perform a laboratory experiment. Conditions can be controlled in
a lab experiment.
In a controlled lab experiment, there should be an independent variable, a dependent variable, and a
control. The independent variable is the factor in the experiment that is manipulated by the researcher.
The dependent variable is the factor in the experiment that changes in response to the independent
variable. Controls in an experiment are used as comparison factors, and they can help determine the
magnitude of the experiment's results.
PERFORMING A FIELD-BASED INVESTIGATION
If an object or organism needs to be studied in its natural setting, a field-based investigation will be
performed. Field-based investigations are often the best way to learn how things work in nature. It is
important to tamper with a natural setting as little as possible when performing these investigations.
OBSERVING AND DESCRIBING OBJECTS, ORGANISMS, or EVENTS
Some investigations focus mainly on observations and collecting large amounts of data. The main purpose
of these investigations is to thoroughly describe specific aspects of nature. For example, a scientist might
collect specimens of a particular kind of insect from many locations. By documenting observations about
the specimens, the scientist can precisely define several general aspects of the insect, such as its color,
leg length, head size, etc. Investigations like this provide a solid base from which more specific,
experimental investigations can develop.
Collect & Interpret Data
Making observations and collecting information are a large part of a scientist’s job. Once this information
is collected, it must be organized and presented in a clear and concise way. Tables and graphs are tools
that scientists use to organize and present information.
Collecting information for scientific investigations is a very important task. Collecting data can be done in
many different ways, such as:
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observing
measuring or counting
asking questions
performing an experiment
Once information has been collected, it should be interpreted. Most of the time, when data needs to be
interpreted, it is placed into tables or graphs.
Tables allow a lot of information to be presented in a small space by organizing data efficiently. The
information found in tables can be interpreted to form conclusions about the data and the topic of the
investigation.
Tables should include all the important data in an experiment, especially the independent and dependent
variables. It is easiest to see patterns in the data in a table if the data is put in order instead of randomly
ordered. For example, the data could be put in order according to the size of the independent variable or
the dependent variable.
For example, if Kolbe is measuring the resistance of various materials, he put the materials in his table in
order of increasing resistance.
Sample ID:
B4
Material
Length Resistance
red/gold metal 1.5 cm
0.5 Ω
A1
silver metal
1.5 cm
2.1 Ω
C10
golden metal
1.5 cm
8.3 Ω
F23
green leaf
1.5 cm
1,275 Ω
Putting the data in this order makes it clear that metals tend to have low resistances. However, there is
one problem with this table: Kolbe did not need to include the length of each sample.
While tables are used for organizing information, graphs are used to present information visually.
Different types of graphs are used for presenting information in different ways.
Circle Graphs
Circle graphs are best used to show how a whole is divided into parts (or percentages of a whole).
Circle graphs, or pie charts, are circular-shaped graphs that are broken into sections. The sections
represent different parts of the whole, and all of the sections combined should add up to the total. Section
sizes in the graph correspond to the percentage or amount of the whole that it represents. For example,
a section that represents 50% of the total should take up half of the graph.
Good examples of questions that may use circle graphs include:
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percentages of students in different classes (out of students in the school)
number of people that reside in each continent (out of entire population)
Example 1:
Anna has a bag of one hundred pieces of candy, which are either purple, blue, red, yellow, or green. She
wants to know which color of candy she has the most of in her bag. She counts the candy and records her
results. From her results, she makes the following graph.
Which color of candy does Anna have the most of?
From looking at the graph, you can tell that Anna has more pieces of blue candy than any other color.
Bar Graphs
Bar graphs are best used to show how a number of objects or events compare in relationship to a single
property.
A bar graph uses bars to compare one property of different objects or events. Each bar represents one
object or event, and there can be two or more bars present on one graph. The bar for each object is a
certain length, which is determined by the amount or occurrence of the property being compared in
relation to the other bars. Thus, the longer the bar, the greater the amount of the object or frequency of
the event.
Bar graphs consist of a horizontal and a vertical scale. One scale identifies the objects to be compared and
the other scale is numerical. The numerical scale must be consistent. A graph can be misleading or
difficult to read if the wrong scale is chosen.
Good examples of questions that may use bar graphs include:
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the favorite color of students in a class
number of each type of animal in an area
Example 2:
Mr. Ward wants to know how much each student in his class participates on a certain day. He decides to
test this by counting the number of times that each student raises his hand during class. Mr. Ward records
his results and makes the following bar graph.
Which student participated the most in class?
Using the number of times a student raised his hand in class to measure the amount of participation,
Ashley participated most in class on that day.
Line Graphs
Line graphs are best used to show a relationship between two measured quantities, usually as a trend
over time.
Line graphs are usually made up of data points on a graph, with a line that connects them or is drawn to
best fit the most points. There are two axes on a line graph. The x-axis, or the horizontal axis, is where
the independent variable (manipulated by the experimenter) is placed. The y-axis, or the vertical axis, is
where the dependent variable (not manipulated by the experimenter) is placed. Line graphs are often
used to see trends over time, with the time normally being the independent variable.
Good examples of questions that may use line graphs include:
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plotting plant growth vs. days
plotting temperature vs. time of day
plotting the year vs. number of animals present in an area
Example 3:
Angie is growing a plant. She measures the plant each week for ten weeks and records the height of the
plant. After the ten weeks, Angie makes a line graph of the information that she collected.
How tall was Angie's plant after 5 weeks?
Angie's plant was 25 inches tall after five weeks.
Scatterplots
Scatterplots are best used to find out whether two variables are related.
A scatterplot is used to examine two sets of data and to investigate the possible relationship (or
correlation) between two variables. The pattern of the points suggests how closely the data are related.
Example: This scatter plot is used to determine the correlation between the number of hours a student
studied and the scores on his tests.
Calculating Mean Value
When interpreting scientific data, often it is useful to find the central tendency or "middle" of a data set.
The mean is one way to calculate the central tendency of a set of data.
Calculating Mean: Add up the numbers then divide by the number in the set to get the mean.
Example: Find the mean of the following: { 66 m, 72 m, 83 m, 89 m}
Mean =
66 m + 72 m + 83 m + 89 m
4
Mean =
310 m
4
Mean =
77.5 m
Units of Measurement
A variety of properties can be used to help identify and classify matter. The major measurable properties
of matter are shown below. When measuring matter, it is important to use the correct measurement units.
Measurable Properties of Matter
Property
Definition
Common Units
mass
the amount of matter in an object
milligrams, grams, kilograms
weight
the force exerted upon an object due to gravity
ounces, pounds, newtons
length
the measure of how long an object is
millimeters, centimeters, meters,
kilometers
volume
the amount of space an object takes up
milliliters, liters
temperature
the measure of "hotness" or "coldness" of an object
or environment
degrees Celsius
density
the amount of matter in an object per unit volume
kg/L, g/mL
Lab Tools
Laboratory tools are used to make measurements and gather data in lab. Knowing how to use these tools
is important for making precise and accurate measurements.
Common laboratory tools include a science notebook, triple beam balance, graduated cylinder, test
tube, beaker, measuring cup, petri dish, hotplate, ruler, spring scale, compass, microscope,
binoculars, hand lens, telescope, stopwatch, and thermometer.
Science
Notebook or
Journal
A science notebook, which may also be called a
journal, is an important tool for controlled
laboratory experiments and also for doing
fieldwork. The hypothesis, procedures, data, and
observations for each investigation should be
recorded using words, pictures, or data tables in
the notebook.
Triple Beam
Balance
A triple beam balance is used to measure the mass
of solid objects. It has three beams that each
measure mass to a different unit place (ones, tens,
hundreds). Units of mass include milligrams,
grams, and kilograms.
Graduated
Cylinder
A graduated cylinder is used to measure the volume
of liquids in milliliters (mL) or liters (L). It is read by
looking at the very bottom of the curve of liquid in
the cylinder. This curve of liquid is called a
meniscus.
Test Tube
A test tube is a long, narrow type of glassware in
which liquids can be stored and heated. Test tubes
have round bases and are stored in test tube racks
or mounted on test tube stands.
Beaker
A beaker is a type of glassware. It can be used to
store liquids, heat liquids, and measure the
volumes of liquids. Beakers have broad, flat bases.
Beakers usually measure liquid volumes in milliliters
(mL).
Measuring Cup
A measuring cup is used to measure the volume, or
amount, of a liquid. To measure how much liquid is
in a measuring cup, look at the lines in the front,
and see what line the top of the liquid is at.
Measuring cups can measure volume in metric
units, such as milliliters (mL), or in U.S. system
units, such as ounces and cups.
Petri Dish
Petri dishes are most often used for growing
cultures of microorganisms, such as bacteria or
mold. They may also be used as containers in the
lab.
Hot Plate
A hot plate is a type of lab equipment used to heat
substances (usually liquids). It has a flat platform
where a beaker containing a liquid can be placed.
Ruler, Meter
Stick, and Tape
Measure
Rulers, meter sticks, and tape measures are used
to measure length. These tools usually have two
edges—one that measures in metric units
(millimeters, centimeters, and meters), and one
that measures in U.S. system units (inches and
feet).
Spring Scale
A spring scale is used to measure the weight, or
gravitational force, of an object. It is used by
attaching an object to the hook at the end of the
scale, then the weight is displayed on the tube of
the scale in Newtons (N) or pounds (lb).
Compass
A compass is a tool that detects magnetic fields.
When no local fields are present, a compass will
detect Earth's magnetic field. The arrow of a
compass generally points North, so a person using
a compass can tell which direction (North, South,
East, or West) he or she is facing.
Microscope
A microscope is used to view objects that are too
small to be seen with the naked eye, such as cells.
Binoculars
Binoculars are used for seeing objects that are
distant, but not as far away as space.
Hand Lens
A hand lens is used to look at objects up close. It
makes objects appear larger.
Telescope
A telescope is used to view objects that are very far
away, such as planets and moons.
Stopwatch
A stopwatch is used to measure time in seconds
and minutes.
Thermometer
A thermometer is used to measure temperature in
either
°C or °F. A thermometer is read by looking at the
number that is displayed at the top of the red line
inside of the thermometer.
Computers & Calculators in Science
It is sometimes useful to use a computer or a calculator to analyze, interpret, or communicate data from a
scientific investigation.
Calculators
Calculators are tools that are used for simple math-related tasks, such as
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basic calculations—addition, subtraction, multiplication, and division
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finding the mean or average of numbers
Computers
Computers are tools that can be used for complex tasks, such as
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calculations with multiple steps
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creating graphs and charts of data
Weather Tools
Meteorologists are scientists who study weather. Meteorologists use several different types of tools to
measure different characteristics of weather.
For example:
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A thermometer is used to measure temperature.
An anemometer is used to measure wind speed.
A wind vane is used to measure wind direction.
A barometer is used to measure air pressure.
A rain gauge is a tool used for measuring the amount of rain that falls in a given period of time.
Thermometer
A thermometer is used to measure temperature in degrees Fahrenheit or Celsius.
Snow Gauge
A snow gauge is used to measure the amount of snow that falls in a given period of
time.
Anemometer
An anemometer is used to measure wind speed in one area.
Wind Vane
A wind vane is a tool used for measuring wind direction.
Rain Gauge
A rain gauge is a piece of equipment designed to measure the amount of rain that
falls in a given period of time.
..
Barometer
A barometer is used to measure air pressure.
.
.
Spectroscopes
Spectroscopes are devices that separate electromagnetic radiation into different wavelengths. These
devices can be used for many purposes. In astronomy, spectroscopes are used to determine what planets,
stars, and other objects are made of. For example, scientists use spectroscopes to separate visible light
from stars into bands of color. By comparing patterns in these bands with known patterns of various
elements, the scientists can determine the stars' compositions.
But stars and planets aren't the only objects that can have their emission patterns analyzed with
spectroscopes. Virtually anything that emits or reflects light can be analyzed with a spectroscope. While
the Sun emits light of almost every visible color (which makes its emission spectrum nearly continuous),
most human-made objects emit only certain types of light.
The spectrum of light emitted by an
incandescent light bulb can be determined
with a spectroscope. Its emission pattern
is shown on the right. This spectrum is
very nearly continuous, making it similar
to sunlight.
The spectrum of light emitted by a
florescent light bulb can be determined
with a spectroscope. Its emission pattern
is shown on the right. This spectrum is not
continuous, since it shows individual
bands of light.
Laboratory and Field Safety
The following rules are essential for keeping you and your classmates safe in the lab:
General Lab Safety
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Read the entire lab procedure before you begin an experiment.
Only perform the assigned experiment when the teacher has given you permission to do so, and
when the teacher is supervising.
Know where all the safety and emergency equipment (e.g. eyewash station, fire extinguisher, fire
blanket, first-aid kit, etc.) is located in the lab.
Only bring necessary materials into the lab area; keep your work area uncluttered.
Personal Safety
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Always wear closed-toe shoes, safety goggles, a protective lab apron or lab coat, and protective
gloves when working in the lab.
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If possible, wear clothes made of cotton. Synthetic materials can melt onto your skin if they catch
fire.
If a chemical gets in your eye(s), go to an eyewash station and flush your eyes with water for at
least 15 minutes. Notify the teacher.
Tie back long hair, and roll up loose sleeves.
Never eat, drink, or apply makeup in the lab.
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Do not touch your face or eyes while conducting an experiment.
If you have to cut something, cut in a direction that is away from your body.
Wash your hands thoroughly with soap and water after completing experiments.
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Chemical Safety
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Never taste any chemicals in the lab.
Avoid contaminating stock solutions; never return unused chemicals to their original container.
Do not directly inhale any gas or vapor; use your hand to waft the fumes toward your nose.
Always pour an acid or base into water, not vice-versa. Use the mnemonic A&W to help you
remember that you should add Acid to Water, not water to acid.
Report any chemical spill to your teacher immediately.
Glassware, Heating, and Electrical Safety
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Do not use glassware with cracks and chips; ask the teacher for a replacement.
Never insert glass tubing into a rubber stopper without teacher permission.
Never use electrical equipment with a damaged cord.
When heating chemicals in a test tube, point the opening of the test tube away from yourself and
others.
Use tongs or insulated gloves to hold or pick up hot objects.
Field Safety
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Notify the teacher of any allergies or medical conditions that you may have prior to going into the
field.
Don't touch any plants or animals without the teacher's permission.
Never put any part of a wild plant in your mouth.
Don't drink unpurified water.
Wear long pants, long sleeves, socks and closed-toe shoes
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Don't wander off alone.
Wash your hands after being in the field.
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Lab Materials
When working with materials in the laboratory, it is important to store or dispose of the materials
correctly. This will help avoid injuries, damage to the environment, and damage to equipment.
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Laboratory Tools
Most laboratory tools can be reused for many experiments, as long as the tools are not damaged.
For example, glassware can be reused as long as it is not cracked or broken. Even if a tool has
come into contact with a harmful material, it can usually be cleaned using a variety of methods.
Sometimes lab materials break or become unusable for some other reason. If a material is
recyclable, such as most plastics, metal, glass, and paper, it should be recycled—but only when it
cannot be reused. A cracked glass beaker or a broken plastic petri dish are two examples of lab
equipment that could be recycled.
Equipment and tools that have been used in the lab should never be reused as food or drink
containers.
Disposal of Materials
Scientists should try their best to reduce the amount of waste generated during an experiment. Not
only does this save money, but it also makes the lab a safer place and helps protect the
environment. Because some waste is unavoidable, it important to know how to dispose of it
properly.
Waste materials that cannot be reused for another lab may be disposed of in many ways. Some of
the main ways are shown below. Always ask your teacher before disposing of any laboratory
material.
Trash Can - The trash can is usually used for the disposal of dry, harmless materials that cannot
be reused or recycled.
Sink - The sink is usually used for the disposal of water. Some chemicals shoud not go in the sink
even though they are not dangerous. For example, corn starch and oil are not dangerous
chemicals, but they will eventually solidify and clog the drain pipes. You should only put chemicals
into the sink if your teacher has told you that it is safe to do so.
Waste bottles - Chemicals should be used sparingly. Any chemical waste should be placed in its
appropriate waste bottle (with a lid) for the teacher to dispose of at the proper time. Different
types of chemical waste should not be mixed together unless a teacher gives specific instructions
to do so. Some chemicals can form toxic fumes or even expolde when they are mixed.
Biohazard container - After a biological material (such as bacteria) is used in an experiment, it
should be sealed and placed in a biohazard receptacle. The teacher will dispose of the stored waste
at the proper time.
Scientific Evidence
The goal of any scientific experiment is to answer a question or to better understand a process or system.
After an experiment is complete, scientists must analyze the data, draw conclusions, and
communicate their results using evidence from the experiment.
ANALYZING DATA
Scientists perform investigations because they are curious. That is, they want to learn more about
something. When an experiment is complete, the scientist studies the data to find out what it means. The
scientists tries to understand how one factor, or variable, in the study affected another. For instance,
imagine a scientist planted 20 bean seeds in each of 7 cups. She placed the cups in each of 7 different
temperatures. If the scientist had gathered the following data:
Temperature Number of Sprouted
(in °F)
Bean Seeds
55
2
60
5
65
7
70
12
75
15
80
9
85
4
she might determine that temperature affects the sprouting rate of bean seeds, and that more of these
bean seeds sprout at 75° than at 55°.
DRAWING CONCLUSIONS
After gathering and interpreting data, a scientist draws conclusions about the hypothesis. The evidence
may prove that the scientist's hypothesis was correct. The evidence could also prove the hypothesis was
incorrect. Either way, the scientist has learned something.
Scientists must check conclusions they and other scientists draw and check each others’ hypotheses,
experiments, and conclusions to make sure that they are accurate.
Checking work is made easier through the keeping of honest, careful records about observations and
experiments. These records should never be changed or altered to fit a conclusion or idea or to hide
something. When reporting what is learned during an experiment, it is important to offer reasons for all of
the findings and to make sure all conclusions are supported by the evidence, and are not made from hope
or guesses.
USING EVIDENCE TO COMMUNICATE RESULTS
Scientists show openness when they are willing to provide all of the information about their experiments
to others. This allows the other scientists to review the work. Sometimes other scientists will disagree
about how to interpret data collected during an investigation. When scientists review the results of
another scientist’s experiment, they are often skeptical. That is, they question the validity or reality of the
data. The scientists may try to learn if the results are reliable by asking the following questions:
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Was the sample size large enough?
Was the experiment controlled?
Are the findings reliable?
Can the data be interpreted in a different way?
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Evaluating Models
Models are objects, drawings, or ideas that are very similar to the real thing, but are different in some
ways.
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A globe, for example, is a model of the planet Earth.
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A globe is a good model of planet Earth. Both objects are round, and have land and oceans shown
on them. However, the model globe is much smaller than the real planet Earth, and it is made of
different materials.
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Although models are always a little different from the real thing, they are very useful for helping
people learn about the real thing.
Another example of a model is a plastic model of a human's inner organs.
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Even though a model of a human's inner organs is different from a real human, it is useful for
helping people to understand where these organs are located in a real body.
History of Science & Technology
"If I have seen further than other men, it is because I have stood on the shoulders of giants."
—Sir Isaac Newton
This famous quote from a letter to Robert Hooke by Isaac Newton expresses how one scientific
discovery or technological advance leads to another. In a very real way, humankind owes
everything it has accomplished in the field of science to every scientist over several thousand
years. Below is a small sample of some of these "giants" in chronological order.
Nicolas Copernicus was born in 1473 to German parents in what is now Poland. At the time
when he began his study of astronomy, the widely accepted theory of how planets and stars
moved had stayed basically the same for over 1,300 years. This ancient model of the universe
originated with the idea that everything should move in perfect circles about the Earth, and it
was adapted to resemble the actual motions of the planets and stars.
Based on his observations and solid mathematical
calculations, Copernicus came up with a model for
the universe in which all the planets including the
Earth revolved around a central point, the Moon
revolved around the Earth, and the Earth rotated
on its axis. Other people followed Copernicus's
lead in conducting scientific investigation
through observation and mathematics, eventually
culminating in the Renaissance.
Harmonia Macrocosmica by Andreas Cellarius
Galileo Galilei was born in Italy in 1564. He made an improved telescope and used it to
study astronomy. He discovered the first moons orbiting other planets—moons of Jupiter.
Galileo conducted systematic experiments in kinematics, studying gravity and how it
accelerated different objects. His support of Copernicus' theory that the Earth was a moving
planet like the other planets was vehemently opposed by major Christian leaders including
Martin Luther, John Calvin, and Pope Urban VIII. Copernicus's theory was considered to oppose
verses from the Christian Bible such as "He [God] has made the world firm, not to be moved."
(1 Chr 16:30)
Robert Hooke was born in 1635 in England. He
contributed to many different fields of science and
technology. He has a law of physics named after him,
was a known rival and opponent to Sir Isaac Newton,
and he later confirmed Anton van Leeuwenhoek's
microbiological discoveries.
Hooke built a compound microscope—a microscope
that used two lenses. He published his observations in
1665 in the popular book Micrographia. This book may
have inspired van Leeuwenhoek to begin building
microscopes.
Using his microscope to examine cork, Hooke became
the first to observe cells and gave them their name.
Image from Micrographia by Robert Hooke,
1665
Anton van Leeuwenhoek was born in Holland in 1632. He became very skilled at grinding
lenses and was able to build simple microscopes that could magnify objects 200 times while
still giving a clear image. This was such a vast improvement over earlier microscopes that some
people consider him to have invented the microscope. His novel, clear view into the microscopic
allowed Leeuwenhoek to observe and describe microorganisms. Because he was the first to
study such tiny life in detail, he is sometimes called the father of microbiology. A replica of
one of Leeuwenhoek's microscopes is shown below.
Image by Jacopo Werther
Isaac Newton was born in 1642 in England. He attended Cambridge University and, while still
young, formulated his laws of motion, calculus, and the theory of gravity. He applied the
law of gravity to explain tides on the Earth and the motion of planets around the Sun. Newton
also contributed to optics and other fields of physics.
James Hutton was born in 1726 in Scotland. His study of geology led him to theorize that the
features of the Earth—mountains, hills, rocks, etc.—were continually being formed and worn
away by processes such as erosion and deposition. He also realized that processes such as
volcanic eruptions and the formation of certain rocks depended on the heat from inside the
Earth.
Charles Darwin was born in 1809 in England. His interests and contributions spanned the
fields of taxonomy (the classification of living things), geology, paleontology (the study of
ancient life forms), and anthropology (the study of humans).
Darwin's time on the ship The Beagle provided
him and other scientists with valuable
observations and samples which led him to form
the theory of evolution by natural selection.
Image by José-Manuel Benitos, reproduced under GNU
Free Documentation License version 1.2
Gregor Mendel was born in 1822 in Austria. He studied the way
physical characteristics of plants were passed down from parents
to offspring. In the process, he formulated three laws of
inheritance that describe how dominant and recessive traits are
passed down through genes. Although Mendel did not use the
word genes, he is considered to be the father of modern genetics.
From Mendel's Principles of
Heredity: A Defence by
William Bateson, 1902
Louis Pasteur was born in France in 1822. After demonstrating that yeast was the cause of
fermentation—the process by which wine and beer become alcoholic—Pasteur went on to study
disease and create vaccines for various diseases. He developed a process, now named after
him, for removing microorganisms from foods and drinks. He used this process to provide
evidence to support germ theory.
George Washington Carver was born into slavery in the United States around 1864. He
spent his life in agricultural research, focusing on helping the poorest farmers in the South. He
helped educate farmers on how to enrich the soil by growing plants like sweet potatoes and
peanuts that put nitrogen back into the soil and by using crop rotation. He developed multiple
uses for crops such as peanuts to create a demand for them, changing the economy of the
South.
Image from This Dynamic Planet,
USGS
Alfred Wegener was born in 1880 in Germany. Coming
upon descriptions of similar fossils found on opposite sides
of the ocean, he spent much of his life gathering evidence
for continental drift. Geologic formations, fossils, and
evidence of ancient climates as well as the shapes of the
continents themselves supported his theory that all the
Earth's continents used to be grouped together as one
"supercontinent" and are in continual motion.
Rachel Carson was born in 1907 in the United States. She was an accomplished writer on the
subject of biology. She is best remembered for her book Silent Spring, which focused on the
effects of pesticides on the environment. Her book sparked a public outcry that led to the
banning of DDT and the founding of the Environmental Protection Agency. Without Rachel
Carson, the bald eagle (among other creatures) would probably no longer be able to survive in
the continental US.
Jane Goodall was born in 1934 in England. She spent years observing chimpanzees in
Tanzania and was for a time accepted by a troop as a member of their social group. Having not
been trained as a scientist before she started her observations, Jane Goodall saw the apes with
fresh eyes—less as objects to be studied and more as unique and complex individuals. She has
dedicated her life to spreading knowledge of great apes throughout as much of the world's
population as she can and works for their preservation.
Impact of Science - Cultural Contributions
Many different types of people, with many different interests, backgrounds, and experiences, have made
significant contributions to science.
Conventional scientists working in laboratories are not the only people who have made major
contributions to the progression of modern science.
Sometimes the focus of science is significantly changed by popular writing and activism. This was the case
with 20th Century author and biologist Rachel Carson and her world famous book Silent Spring. In the
book, which was published in 1962, Carson revealed some of the potential threats of using inorganic
chemical pesticides in agriculture. The response to Carson's book was so large that a now large and
powerful government agency, the Environmental Protection Agency, was created as a direct result.
Another unconventional scientists was Percival Lowell, who had been a successful businessman in the
late 19th Century, but then turned virtually all of his attention to astronomy. Lowell established the
Lowell Observatory in Flagstaff, Arizona, which was the first observatory ever deliberately built far from
civilization and at a high altitude. Lowell is best remembered for his efforts to verify that there are canals
carved into the surface of Mars; an idea that has since been disproved. But Lowell's detailed observations
and sometimes wild theories eventually led to the discovery of Pluto, formerly considered to be the ninth
planet in our solar system.
Sometimes scientific discoveries powerfully impact human culture, society, business, and beliefs.
Nicolaus Copernicus was one scientist whose theories about the heliocentric nature of the universe
significantly impacted astronomy as well as the dominant beliefs of his time. Copernicus' observations
about the movement of the other planets in the early 16th Century led him to believe that the Earth and
all of the other planets revolve around the Sun. Copernicus was the first to popularize this model of the
universe. It had been previously believed that the Earth was the geometric center of the universe.
In more recent times, some of the more groundbreaking scientific discoveries have come from
investigating the world of the very small. Luis Alvarez was a world famous particle physicist and
inventor, who won the Nobel Prize in Physics in 1968 for investigating resonant states of atomic nuclei;
his findings helped develop the first devices capable of observing the ultra-small quantum properties of
nuclei. He also aided in research headed by his son, which led to the modern theory of the dinosaurs'
extinction.
Louis' son, Walter Alvarez, became a famous scientist in his own right. Walter conducted research in the
1960s looking into a transition between two geologic periods, which took place about 65 million years ago,
the same time the dinosaurs went extinct. This geologic boundary, he found, had extraordinarily high
levels of a metal whose presence could only be explained by an asteroid impact with Earth. This discovery
led to the now dominant theory that most of the animals alive during the age of the dinosaurs became
extinct after a massive asteroid struck the Earth.
Antoine Lavoisier & Conservation of Matter
In the late 1700s, Antoine Lavoisier conducted experiments in which he carefully measured the masses of
all the substances involved in various chemical reactions, including the gases used and those given off.
What he found what that the total mass before and after a chemical reaction was always the same.
Antoine Lavoisier was a French scientist who contributed significantly to chemistry. He is partially
responsible for developing the law of the conservation of mass/matter in chemical reactions.
Antoine Lavoisier helped to develop the idea of the conservation of matter.
The conservation of matter (or mass) principle states that in any isolated system, the total amount of
mass in that system will be constant through time.
So when Lavoisier conducted his experiments, he saw chemicals changing into other chemicals, liquids
changing to gases, solids changing to liquids, and many other transformations. However, over the course
of all of these transformations, even though the type of matter he had changed, the total mass of that
matter did not change.
The Curies & Radioactivity
Scientists estimate that the Earth's age is nearly 4.6 billion years. This age has been calculated from the
radioactive decay of specific radioactive elements.
This age was not immediately arrived at by scientists in the late 1800s and early 1900s. This was
because, at this time, different ways for calculating the age of the Earth were yielding different results.
In the late 1800s, William Thomson (known as Lord Kelvin), calculated that the Earth was only about 40100 million years old. This calculation was based on the planet's current temperature near the surface.
Kelvin assumed that the Earth began as a hot, molten mass of liquid rock. From this initial temperature,
Kelvin then was able to figure out how long it would take the Earth to cool to its present temperature.
Kelvin's results were not looked upon favorably by a number of prominent scientists of his time, though
virtually everyone agreed that he had made no errors in his math. Thomas H. Huxley, for one, argued that
Kelvin's result was entirely too short an amount of time to account for all of the biological evolution that
had taken place in Earth's history. Geologists also found an age as low as 100 million years extremely
difficult to accept.
As it turned out, Kelvin (as well as a number of other scientists) had based his calculations on faulty
assumptions. Specifically, until 1896, no one had any idea what radioactivity was, or what role it has
played on planet Earth.
DISCOVERY OF RADIOACTIVITY
Radioactivity was discovered by accident by French scientist Henri Becquerel in 1896.
This discovery helped to explain how the Earth could be billions of years old, but still be relatively warm.
Henri Becquerel discovered radioactivity in his laboratory, when he was attempting to show that uranium
was phosphorescent.
Phosphorescent materials can absorb energy, such as light from the Sun, and then re-emit this energy
later. Becquerel found that uranium kept emitting energy, well after it had been exposed to light. This
meant that the energy it was emitting must be coming from within.
MARIE AND PIERRE CURIE
After radioactivity was discovered, scientists Pierre and Marie Curie were among those who worked to
figure out exactly what it was.
Pierre Curie and Marie Curie in their laboratory in France
The pair isolated two new elements that were the source of most of the radioactivity of uranium ore. They
named one radium because it gave off powerful invisible rays, and the other polonium in honor of Marie
Curie's country of birth, Poland.
The Curies also showed that the amount of radiation that came from these elements changed as the
amount of radioactive material was changed. This demonstrated that radioactivity must come directly
from each individual atom's nucleus.
For this work, Pierre and Marie Curie won the Nobel Prize in Physics for 1903. Eight years later, Marie
Curie became the first person to win a Nobel Prize in two different fields, when she won it again for
chemistry.
RADIOACTIVITY AND THE EARTH'S AGE
The discovery of radioactivity and the work of scientists like the Curies helped to explain how the Earth
could be billions of years old, but still be relatively warm.
Scientists learned that new heat is continuously produced in the Earth's interior by radioactive elements.
Eventually, it was shown that the rate of heat flow from Earth's interior has been relatively constant for a
very long time, and that Kelvin's estimate for the age of the Earth was far too low.
Since Kelvin's time, it has been learned that the Earth is not a completely solid rock, but that it has many
layers and contains radioactive elements in its interior.
Unlike Kelvin's idea, scientists' understanding of radioactivity has allowed for a much longer expanse of
time between the Earth's initial molten state and the present. This is because much of the heat escaping
the Earth is not left over from the Earth's initial molten state. Instead, much of the heat is continuously
produced by radioactive decay in the Earth's interior.
Studies of specific radioactive elements have provided estimates for the ages of many geologic features,
prehistoric events, and the age of the Earth itself.
Based on rates of radioactive decay, the Earth is estimated to be nearly 4.6 billion years old.