Chapter Twenty-two — Good-bye to All That
A Short History of Nearly Everything – by Bill Bryson
Chapter 22 — Good-bye to All That
- Lichens are about the hardiest visible organisms on Earth, but among the least ambitious. They will grow happily enough in a sunny churchyard, but they particularly thrive in environments where no other organism would go (on blowy mountaintops and arctic wastes, wherever there is little but rock and rain and cold, and almost no competition.
- Lichen are in fact a partnership between fungi and algae. The fungi excrete acids that dissolve the surface of the rock, freeing minerals that the algae convert into food sufficient to sustain both. It is not a very exciting arrangement, but it is a conspicuously successful one. The world has more than 20,000 species of lichens.
- It can take more than 50 years for a lichen to attain the dimensions of a shirt button.
- Attenborough has stated, “Life, even at its simplest level, occurs just for its own sake.”
- If you imagine the 4.5 billion years of Earth’s history as a 24-hour period, it would be divided as follows:
- 4:00 am – the rise of the first simple, single-celled organisms
- 8:30 pm – the first sea plants appear
- 8:50 pm – the first jellyfish arise
- 9:04 pm – trilobites swim onto the scene
- 10:00 pm – plants pop up on land
- 10:05 pm – the first land creatures arise
- 10:24 pm – the Earth is covered in carboniferous forests
- 10:25 pm – the first winged insects appear
- 10:58 pm – dinosaurs plod onto the scene
- 11:39 pm – dinosaurs vanish off the Earth
- 11:40 pm – the age of mammals begins
- 11:58 pm – humans arise
- Another way of visualizing the sweep of Earth’s history is to stretch one’s arms to their fullest extent and consider this as the whole of Earth’s existence. On this scaled, the distance from the fingertips of one hand to the wrist of the other hand is the Precambrian period. All of complex life is measured by the distance of one hand, “and in a single stroke of a medium-grained nail file you could erase human history.”
- Oxygen levels in the Devonian and Carboniferous periods, when terrestrial life first bloomed, were as high as 35% (the level is 21% now). This level allowed animals to grow to remarkably large sizes.
- Scientists can determine the levels of oxygen and other gases eons ago by using isotope geochemistry.
- The oldest indicator of a surface animal yet found is a track left 350 million years ago by a millipede-like creature on a rock in Scotland. It was over 3 feet long. Millipedes would eventually reach lengths of six feet. During the high oxygen level eras, dragonflies were as large as ravens. Tree ferns have been found that were 50 feet in length.
- Extinction has been very common among on Earth. It is estimated that 30 billion different species of organisms have existed, and 99.99% of those species have gone extinct.
- Earth has seen five major extinction periods – Ordovician, Devonian, Permian, Triassic, and Cretaceous. During the Permian extinction, at least 95% of animals known from the fossil record went extinct, and one-third of the insect species went extinct also.
- Many reasons have been proposed as causes for extinction, including global warming, global cooking, changing seal levels, oxygen depletion of the seas, epidemics, giant leaks of methane gas from the seafloor, meteor and comet impacts, runaway hurricanes known as hypercanes, volcanic upswelling, and catastrophic solar flares.
- The KT meteor impact (Cretaceous-Tertiary impact near the Yucatan Peninsula) was positively enormous. It struck with the force of 100 million megatons. If you were to explode one Hiroshima-sized bomb for every person alive on Earth today, you would still be about one billion bombs short of the destructive power of the KT meteor impact. It impacted Earth in an area where the rock was rich in sulfur, and the explosion turned an area about the size of Belgium into a gaseous sulfuric acid production area. The KT impact wiped out about 90% of land-based species but only 10% of species living in water. Water offered protection from the heat and flame. The land creatures that did survive were small and furtive. They were warm-blooded, nocturnal, flexible in diet, and cautious by nature.
- As species developed after the KT impact, some of them expanded prodigiously. There were guinea pigs the size of rhinos and rhinos the size of a two-story house. Early members of the raccoon family evolved in creatures the size of bears. One bird species called Titanis was ten feet high, weighed over 800 pounds, and had a beak that could tear the head off of most other species.
- Our fossil record is extremely scant. For the whole of the Age of Dinosaurs, less than 1000 species have been identified, and half of those are from one specimen only.
- “Humans are here today because our particular line never fractured – never once at any of the billion points that could have erased us from history.”
- Lessons to be learned? 1) Life wants to be 2) Life usually doesn’t want to be much 3) Life from time to time goes extinct 4) Life goes on!
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