Life of Earth
53 quotes
"Your cells contain not only the genetic instructions for making a human body but also old genes that the cells of your evolutionary ancestors used. These old instructions are crammed into your chromosomes like old memorabilia in an attic."
"Almost all generic diversity is in bacteria, archaea, and protists. The fungi, the plants, and all the animals are only a subset of the variation within the protist group."
"There is about as much genetic difference between a bacterium in the soil and an archaean in a hot spring than there is between a bacterium and you."
"Even the little bit of wobbling that Earth does experience has been enough to cause about twenty ice ages during the last two million years of Earth's history. We have the moon to thank for the relative stability of Earth's movements."
"Two hundred fifty million years ago, at the end of the Permian period, volcanoes in what is now Siberia erupted for about two hundred thousand years, producing layer after layer of lava; the deposits are called the Siberian Traps. The sulfur dioxide from these eruptions caused acid rain, and the carbon dioxide caused global warming, extensive enough to have at least initiated the greatest mass extinction in Earth's history: the Permian extinction wiped out about 95 percent of species. Biodiversity recovered after this event, but the recovery took almost one hundred million years."
"The origin of life itself was a lucky accident. When the oceans formed on an Earth no longer molten, conditions were hellish. ...scientists call this the Hadean period, named for Hades...Within a few hundred million years, these oceans were filled with living cells that resembled living bacteria. ...the kind of sheer luck that [may have] occurred on only a very few planets."
"As the continents arose from the oceans, minerals in the exposed rocks reacted with carbon dioxide and created inorganic limestone. At the same time, many microscopic photosynthetic organisms have carbonate shells. ...they settle to the bottom of the sea, causing a buildup that eventually becomes organic limestone."
"There has always been enough carbon dioxide to keep the Earth warm enough for life, but not too much to bake it to death."
"You may be nothing more than a complex set of chemical reactions. Solar energy raises the electrons of atoms to high levels of energy in photosynthesis, and all other metabolic reactions allow the energy to flow to background levels."
"Most enzymes are lumpy proteins that have little grooves in them into which molecules can slip and react."
"Enzymes are biological catalysts. ...Cats are also catalysts. If you wait long enough, everything in your house will eventually end up on the floor. Cats merely make them end up on the floor more quickly. ...Enzymes facilitate the natural tendency toward molecular breakdown, but they also defy this natural tendency, as long as the necessary energy and instructions are provided."
"The instructions for making... enzymes comes from DNA molecules. The DNA that encodes the instructions for one kind of enzyme, or a related set of enzymes, is called a gene."
"When one DNA molecule becomes two, the new strands are almost identical... Occasional mistakes occur during the copying process. These mistakes are called mutations. ...Most mutations... are small and have little or no significance on the organism."
"Nature selects the superior mutations. ...That is all evolution is. And there is no way in the universe to stop it, so long as no catastrophe wipes out the evolving population."
"Scientists... have used selection to get populations of bacteria to evolve the ability to use different kinds of sugar... or to tolerate different temperatures, in just a few weeks or months."
"It takes only a few years for populations of bacteria to evolve resistance to any particular kind of antibiotic..."
"Directional selection causes the average population trait to change... Stabilizing selection occurs when the average population trait remains unchanged. ...This pattern has been called stasis, or equilibrium."
"When conditions change, directional selection gears up to make the population change along with it. ...sometimes environmental conditions change and then do not change back. ...Under these circumstances, directional selection has permanent and rapid effects. ...Such bursts of evolution have been called punctuations."
"There never was a Garden of Eden, but there was, perhaps, a Garden of Ediacara... blob-like creatures that lived in the sea..."
"Squirrels are not very good predators. But if a nice dinner of meat is presented to them, who are they to turn it down. ...[a] colleague, an ornithologist, captures birds in mist nets... He discovered that a cow had been walking along the nets and biting the heads off the birds. ...another colleague ...told me that it is necessary to use two layers of chicken wire ...to protect chicks from being eaten by deer. Nonhuman vegetarians, like most human vegetarians, are tempted by meat."
"Scientists today understand that there is no single, upward staircase of evolutionary progress. All species are equally evolved."
"In some ways, bacteria can be seen as the most successful life-form on the planet. There are more bacteria, and more kinds of bacteria, than any other group of organisms. They live in a greater range of conditions and have persisted for three and a half billion years."
"Natural selection capitalizes on whatever works, whether it is of greater complexity or greater simplicity..."
"Evolution has no guiding mind or innate direction. It has simply made use of new opportunities: complexity, symbiosis, sex, and altruism."
"This is why evolution appears to have a direction: there are many more ways to become complex than to become simpler."