Oceans in Crisis - Ocean Worlds: The Story of Seas on Earth and Other Planets - page 183

human modification of the ocean is apparent. Here, the dead zones
are spreading.
The term 'dead zone' is a striking one, but in this case the term
reflects contemporary reality. The world today is crowded, and 7 bil-
lion people are currently only being kept alive because we have
invented means to supercharge soil fertility to boost crop yields far
above what would naturally grow. One of the sources of this fertility
is additions of phosphate 106 which, in the past, was supplied by
manure, by Chilean guano, by crushed animal bone from the slaugh-
terhouses, by fossilized dinosaur bone (this was a thriving and very
profitable trade in England for several decades), and even human
bone. In the nineteenth century, gangs of English labourers roamed
the battlefields of Europe, scouring them of the bones of millions of
dead soldiers to transport back, grind up, and spread on the fields—to
the horror of delicately natured observers. In perhaps the most bizarre
example, a large nineteenth-century find of ancient Egyptian mum-
mified cats from Egypt was sacrificed (one more time, perhaps) to
help the crops grow. It is a measure of how desperately sought this
nutrient was—and still is, for there are fears that our current supply,
from phosphate rock strata, will, sometime soon, fail to meet
demand.
The other main means to supercharge our soils, nitrogen, is in
more abundant supply as it makes up most of the atmosphere. But
fixing it into a form that can be absorbed by plants is trickier. Certain
bacteria do this naturally, but too slowly for our current insatiable
demand. When Fritz Haber (who we met in Chapter 4, seeking gold in
seawater), together with Carl Bosch, invented a means of artificially
creating nitrogen-based fertilizers from atmospheric nitrogen, the
stage was set for the subsequent more-than-tripling of human popu-
lation. The associated perturbation of the global nitrogen cycle has
been said to be the greatest since Precambrian times. 107 Since the