Geoscience Reference
In-Depth Information
the trappings of the phlogiston theory, he correctly recognized oxygen
as an element and gave it the name we now know (meaning “acid pro-
ducer”). He too, like Scheele, explored the role of oxygen in respiration,
and more accurately than Scheele, he estimated that oxygen comprises
about 25% of Earth's atmosphere.
Many have complained that Lavoisier gave scant credit to Priestley
and no acknowledgement to Scheele in his own writings about oxygen.
Indeed, Lavoisier claimed never to have received Scheele's letter, al-
though it surfaced among Lavoisier's wife's effects in the 1890s. Did
Lavoisier receive the letter but bury it in his wife's things so he could
claim credit for the discovery of oxygen? Or, did his wife receive the
letter first and hide it so that Lavoisier could claim credit without the
knowledge of a competitor?
5
We will never know, but clearly, as often
happens in science, our ability to explain the world within an existing
paradigm becomes so inadequate that new thinking is necessary. Clearly,
the time was ripe in the early 1770s for the discovery of oxygen.
Let's continue with our brief historical digression. Although Scheele
experimented extensively with plants, he never uncovered the process
of photosynthesis. Priestley did, however, and in 1771, even before he
discovered oxygen, he had found that plants provided a substance that
could sustain a mouse and the burning of a candle. Most, however,
credit the Dutch physician Jan Ingenhousz for fully understanding how
photosynthesis works. By 1779, Ingenhousz was able to summarize his
discovery, in surprisingly modern terms: “It will, perhaps, appear prob-
able, that one of the great laboratories of nature for cleansing and puri-
fying the air of our atmosphere is placed in the substance of the leaves,
and put in action by the influence of the light.”
6
We can see that by the
end of the 1700s, there was a reasonably good understanding of the
major chemical composition of the atmosphere, including the origin of
oxygen and its role in respiration.
In the remainder of the chapter, we will continue to explore history,
but of another kind. Our goal will be to understand the evolution of
photosynthetic oxygen production on Earth. I hope we can agree that
this event was one of the major transforming events in the history of
life. With no oxygenic photosynthesis, there would be no oxygen in the
atmosphere; there would also be no plants, no animals, and nobody to
tell this story.
