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There are creatures that do not seem to have a natural limit on their life span. They only die when they are killed by accident or the action of sickness parasites and pathogens. Other creatures are apparently programmed to die at a given time, and under a given set of conditions. So why do we die? What is death for?
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This episode turned out to be both long and hard. Feel free to snicker at this point. It was long because I couldn’t resist the numerical pun. To match this episode’s number with its subject, I had to squish together the development of eukaryotes with the development of sexual reproduction. Fortunately, they may both have come about because of interactions taking place within microbial mats. It was hard because the subject turns out to be more complicated than I had thought.
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Sometimes, a new species will come into being, and explode across the planet. The population increases drastically within a short time period as they learn to use new materials and new forms of energy. Sometimes, they produce material that is poisonous to forms of life that previously hadn’t encountered such substances. Many species can be pushed to the edge of extinction and beyond. This happened approximately 2.5 billion years ago, with the rise of cyanobacteria. The toxic material that was being produced was oxygen. Though it was catastrophic at the time, the presence of oxygen allowed for a new form of life, which could use the free oxygen as an energy source. This allowed for the arrival of the animals, and eventually, us.
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This is probably the least coherent episode to date. Though the precursors of life can apparently be produced by processes taking place anywhere from the deep sea to deep space, how to get from those starting chemicals to a living cell is still unknown. Rather than a lack of theories, there are just too damn many of them, all of them seemingly at least plausible, and little or no way to decide between one or another. Perhaps they all happened. Perhaps none of them. Perhaps the actual process has yet to be described. Perhaps pieces of the puzzle simply took too long, or require temperatures and pressures that cannot be reproduced in a laboratory.
Here’s a link to a Nova special on this subject that covers it much better than I have. Mind you, they had 45 minutes to do it in, rather than the 9 minutes and change I had.
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It is theorized that our moon was formed when our planet was struck a glancing blow by an object roughly the size of Mars. The notion is known as the giant impact hypothesis. If such a large impact happened to our planet, what about the other planets. How common are giant impacts within our solar system? From the loss of the outer layers of Mercury, to the two-faced appearance of Mars, to the tipped over condition of Uranus, it seems that about half our planets were struck hard enough, by large enough objects, to have a major effect on how the planets appear today.
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According to the rare Earth hypothesis, see episode 59, a large moon is needed for the development of complex life. Our moon isn’t the biggest moon in our solar system; but the moons that are bigger are orbiting much larger planets. Our moon is the largest as a percentage of the planet it orbits. Measured in that way, no other moon comes close. So how rare is such a large moon? Where did our big beautiful moon even come from?
Here are some articles about our moon and where it may have come from.
Giant Moon-Forming Impact On Early Earth May Have Spawned Magma Ocean
New Moon-Formation Theory Also Raises Questions About Early Earth
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Today, we consider all the large planets orbiting stars other than our sun, and their tendency to adopt eccentric orbits. The possible reasons include close encounters with other stars, interactions between the planets themselves, and different ways the large planets may have formed.
Here’s an article on the large size of Jupiter, and the core accretion model, versus disk instability as possible explanations.
Here are several articles on computer simulations of planet to planet interaction, which could cause orbits to become eccentric, or planets to adopt a short-term nearly circular orbit, or even flip over.
Mystery Solved: How The Orbits Of Extrasolar Planets Became So Eccentric
The Architecture of Planetary Systems
Orbit Flips in Exoplanet Systems
Toward the end of the episode, I referenced a couple of earlier episodes. Here are links to said episodes.
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According to the “rare earth” hypothesis, see episode 59, one of the requirements for the development of complex life is a stable, and nearly circular orbit. If the orbit is too eccentric, the planet would be cooked during one part of its year, and frozen most of the rest of the time. That would mean the temperature extremes would be too much for complex life to arise. Since our solar system has planets with roughly circular orbits, it was assumed that such orbits were common. Once we started detecting planets around other stars, we found many planets whose orbits were anything but circular. As it happened, the methods first used to detect exoplanets, see episode 56, were much better at finding very large planets. More recent methods, see episode 57, have allowed us to look at planets that are closer in size to our own Earth. A recent study suggests that Earth sized planets are far more likely to adopt roughly circular orbits, a hopeful sign for the occurrence of complex life elsewhere in our Galaxy.
Here are a couple of articles about the study. Both of them say about the same thing, but each one includes slightly different details.
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After a somewhat disjointed primer on organic chemistry, we talk about how the radiation of a protostar, bathing the protoplanetary disk, See the previous episode, can create the early chemical building blocks of life. This has happened in laboratory experiments, and the chemicals have been observed around young stars, in the material of comets, and in meteorites. This suggests that the very beginning of what would become life, happened during the very beginning of what would become our solar system, while we were not quite a star, not quite a planet and not quite life.
Here are a couple of articles about the laboratory experiments.
Amino Acids and Their Production during the Photolysis of Astrophysically relevant Ices
‘Building blocks for life’ may originate in space
Here are a couple of articles about sugar, detected in space!
Sugar Found In Space: A Sign of Life?
Space Sugar Discovered Around Sun-Like Star
Here’s an article on when a space craft examined material from a comet, discovering amino acids.
Building Blocks of Life Found in Comet’s Atmosphere
Burning through the atmosphere can get warm enough, but here’s an article that describes a meteorite that was heated much more, before it wiazed through the air and hit the surface of Earth. And yet, it still brought amino acids along for the ride.
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As a nebula collapses, there are forces which resist the collapse. Things like rotation, ionization and heat can overwhelm gravity and keep a given chunk of dust and gas from ever managing to start nuclear fusion and become a star. Those same forces, if the cloud manages to become a star, can help to form planets.
Here’s an article on how our solar system got the infusion of heavy elements needed to form rocky planets like our Earth.
A Step closer to understanding the birth of the sun
Here’s an article on an early stage collapsing cloud of dust and gas in the Eagle Nebula that has roughly the same amount of material as our solar system.
And here’s an article wherein a protostar was observed to increase in temperature, possibly from the in fall of material from its surrounding disk.