Answer 1:
Scientists can tackle questions like yours in a
few general ways. In empirical studies, scientists
look for answers by measuring the variables of
interest. To answer your question empirically,
researchers would have to put rats in chambers and
measure their output of methane (and similar
gases). That would be pretty pricey and I
doubt anyone would get funding for it. Another
issue is the variation in rat diets. Rats are
generalists. They’ll eat anything from peperoni
pizza to peanut butter. Since different foods have
different abilities to produce flatulence, it
would be difficult to come up with one answer.
Research on cow gas production is
interesting enough to get funded. Cow
digestive systems are basically big fermentation
tanks. So how would one measure bovine gas
output? This clip shows one system in action:
cow farts
This system collects gas that can be analyzed
later to determine which gases are being emitted.
Most of the gas that comes from the far end of the
digestive tract is carbon dioxide. Like any
mammal, cows also expel carbon dioxide when they
breathe. But they also burp up a lot of
methane. So the methane production has to
be measured at the cow’s mouth. Total gas
production for one or a few cows can be measured
empirically.
But how do scientists know the amount of gas
emitted by all cows? Often scientists have to
use estimates and models. For example, they could
take data from a few cows, find an average, then
multiply that by the total number of cows on
Earth. But they need to estimate the total number
of cows, it’s not as though every cow has a
license. Plus, different cows are different sizes
and eating different foods. According to one
source (
cow farts problem ), “livestock pushed
about 119.1 million tons of methane into the air
in 2011 alone.” A different team of
scientists might have slightly different estimates
or assumptions and arrive at a different total,
even using the same base data. That doesn’t mean
that models are useless though. They are usually
critical in determining the highest and lowest
likely values.
Even though there are many, many rats on earth,
they do not have a digestive system based on
eating low-quality food, fermenting it, burping up
cud (partially digested food and bacteria), then
fermenting it some more. So I’m going to say
that cows produce a lot more gas.
Notice that I arrived at this conclusion by
reasoning and applying what is known about the
species. That is another way to get reasonable
answers in science; using facts and logic to
reach a conclusion.
If you wanted to estimate the total number of
rats on earth, how would you do it?
Thanks for asking.
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