Oxygen, a colorless gas that is otherwise known as Element
Number 8 on the Periodic Table of Elements, is the most reactive gas of the
non-metallic elements and comprises about 21% of the Earth’s atmosphere.
According to a study funded by NASA, Oxygen has been present
on the earth for approximately 2.3-2.4 billion years, and it began to appear in
our atmosphere at least 2.5 billion years ago. While it is not entirely clear
why oxygen abruptly became such a prominent element in the Earth’s atmosphere,
but many assume that geologic changes on the earth played a large role in the
process.
Oxygen has the atomic number 8, the atomic symbol O, and an
atomic weight of 15.9994. According to the Thomas Jefferson National
Accelerator Facility, oxygen is the third most abundant element in the
universe. Organisms that use oxygen to breathe, known as cyanobacteria, inhale
carbon dioxide and breathe out oxygen through photosynthesis, as do modern-day
plants. It is likely that cyanobacteria are the cause of the first apparition
of oxygen in earth’s atmosphere, which is a phenomenon referred to as the Great
Oxidation Event.
The photosynthesis of cyanobacteria was probably occurring
long before a significant amount of oxygen was accumulated in the earth’s
atmosphere. A study published in the journal
Nature Geoscience in 2014 discovered that oxygen generated from photosynthesis
began in marine environments approximately half a billion years ago prior to it
beginning to accumulate in the atmosphere about 2.5 billion years ago.
While those living on earth today are very dependent on
oxygen, the beginning accumulation of this element in the atmosphere was
somewhat disastrous. The atmospheric change led to a mass extinction of
organisms that do not need oxygen, known as anaerobes. These anaerobes that did
not have the ability to survive in environments with oxygen began to die off.
The initial indication to humans that oxygen existed in the
atmosphere occurred in 1608, when Cornelius Drebbel, a Dutch inventor,
discovered that heating potassium nitrate resulted in the release of a gas.
That gas remained unidentified until the 1770s, when three chemists began to
discover it around the same time. Joseph Priestly, an English chemist was able
to isolate oxygen by using sunlight to sign light on mercuric oxide and then
collecting the gas that was generated as a result of the reaction. Preistly
published this discovery in 1774, becoming the first scientist to actually
publish these oxygen-related findings. Oxygen was given its name from the Greek
words “oxy” and “genes,” which together mean “acid-forming.”
While the presence of too little oxygen can pose a threat,
so can the pretense of too much oxygen. For example, around 300 million years
ago, the earth experienced atmospheric oxygen levels of 35% and insects grew to
extreme sizes.
Oxygen is formed through the fusion of a carbon-12 and a
helium-4 nucleus inside the hearts of stars. However, recently, scientists have
gained the ability to study the structure of oxygen by looking at its nucleus. And in March of 2014, a physicist at North
Carolina State University and his team discovered the nuclear structure of
oxygen-16. This is important because it helps us understand the process of
nuclei formation in stars.
An additional set of researchers placed their focus on
oxygen’s role in life on Earth. According to researchers at the University of
Southern Denmark, animal life did not appear on Earth until much later than the
Great Oxidation Event, with simple animals appealing just around 600 million
years ago. While many theorize that the appearance of oxygen led to the
existence of animals, animals were actually not present on earth during the
first prominent rise of oxygen levels in the atmosphere. On the contrary, it is
believed that something other than the appearance of oxygen caused the first
rise in animal life. While it may be true that rising levels of oxygen led to
varied and diversified ecosystems that are present today, there are still
several modern-day animals that can survive in extremely low-oxygen areas in
the ocean.