----------------------- 2744 - LIFE - will we find it on other planets?
-
- Planet Earth has been around for the past 4.5 billion years, or, the last third of the Universe's history. We can trace the existence of life back more than four billion years, teaching us that life arose on Earth very early on. If it wasn't immediately coincident with the formation of our planet, it certainly arose within the first few hundred million years of Earth's history.
-
- Life survived and thrived for billions of years before human beings arose. Apparently we are the first intelligent and technologically advanced species on our planet. How likely is there similar life in the Universe? How likely is there intelligent life?
-
- While we haven't found either beyond Earth just yet. We have not determined whether that life either "rarely", or, "commonly" occurs on Earth-like worlds. We are beginning to conclude that life may be common, but “intelligence” is rare. Here's why:
-
- Here on Earth, life arose very early on in our planet's history, while intelligent life only arose after billions of years of successful other life. This history can help us estimate probabilities for whether life is common or rare, along with intelligent life's likelihood, on Earth-like worlds.
-
- It's very difficult to know what the true probability of life arising on Earth is, or what the odds that intelligent, technologically advanced life would arise. In order to know such a thing, what we would ideally want to do is to create that same environment that was present on Earth back at the time of its formation many times over, watch each of those environments evolve over 4.5 billion years, and see what comes out.
-
- That is how science ideally works at a fundamental level: experimentally. You want to know something about the behavior of a system, so you create that system and observe its behavior over and over again. When you have a large enough sample size, you see what the results are and draw your conclusions based on that. It's the simplest approach to any “scientific question“.
-
- The evolution of the atmosphere is one of the strong indirect pieces of evidence we have for Earth having an active biological history going back all the way to immediately after its formation.
- Although the exact ratios of the different atmospheric components of Earth throughout its entire history are unknown, there were large amounts of methane present in the atmosphere prior to 2.5 billion years ago and virtually no oxygen. With the arrival of oxygen, the methane was destroyed, and the planet's greatest ice age began.
-
- Trilobites fossilized in limestone are organisms can have their lineage traced back to a universal common ancestor that lived an estimated 3.5 billion years ago, and much of what's occurred in the past 550 million years is preserved in the fossil records found in Earth's sedimentary rocks.
-
- In reality, you might only have one planet around one star, but if you could know the outcomes of a very large number of systems that were made of identical planets around identical stars, you would know what the probability was of your particular planet getting a specific outcome. Just as you know the probability of getting two six-sided dice to sum up to 7 is one-sixth, you could know the probability of life (or intelligent life) arising on Earth.
-
- But in practice, we cannot take this approach for planet Earth. With only one system, we cannot perform the experiment many times and determine the frequency of the desired (and undesired) outcomes.
-
- In Bayesian probability, the reasoning goes backwards instead of forwards. What you are evaluating isn't the overall probability of outcomes, but rather the probability of one particular hypothesis being valid compared to all the possible hypotheses. It's the best tool to use when you only have one system with one outcome.
-
- To give an example for planet Earth: We know that life arose on Earth relatively early on. The earliest fossils go back 3.8 billion years and there are zircon deposits that are thought to have a biological origin that go back 4.1-to-4.4 billion years, and our planet is only about 4.5 billion years old.
-
- On the other hand, complex life didn't arise until shortly before the Cambrian explosion , just 600 million years ago, and intelligent, technologically advanced life only came to be with the arrival of human beings.
-
- That's our one system, along with its outcome. An ocean-covered planet with a modest CO2 atmosphere, with the other properties of planet could potentially be an inhabited planet suitable for life arising on it.
-
- We cannot responsibly call a planet 'Earth-like' or not until we understand more about what conditions lead to which outcomes. So, what are the possible hypotheses that could lead to this? Realistically, there are only four.
-
---------------- Life commonly arises on planets like Earth, and becomes intelligent frequently.
-
---------------- Life commonly arises on planets like Earth, but becomes intelligent only rarely.
-
---------------- Life only rarely arises on planets like Earth, but when it does, it becomes intelligent frequently.
-
- --------------- Life only rarely arises on planets like Earth, and when it does, it becomes intelligent only rarely.
-
- You could start off with billions of planets around billions of stars that were decidedly very much like Earth, and watch what unfolded. Unfortunately, we absolutely cannot do that; we don't even know what it is that makes a world "Earth-like" in any meaningful way. There is too much we don't know to even talk about "Earth-like" planets with any confidence whatsoever.
-
- But with Bayesian probabilities, you can do more than just throw up your hands in surrender. You can assume, as a starting point, that each of the relevant questions has a 50:50 probability, where there's a 50% chance that life arises commonly and a 50% chance that it arises only rarely. Similarly, assuming life arises, there's then a 50% chance that it becomes intelligent frequently and a 50% chance that it becomes intelligent only rarely.
-
- What you then do is “model“, based on the probabilities you assumed, how frequently you get an outcome that aligns with the observed results. In this case, getting life and/or intelligent life out of them in a way that aligns with what happened on Earth.
-
- Bayesian probabilities cannot tell you what the actual odds of these outcomes are, but they can tell you which hypothesis is more likely, and by how much, which is useful information for "betting odds." If there's no meaningful information, the initial probabilities you assumed (50:50 for each case) will be unchanged. However, if the analysis favors one hypothesis over another, you'll see your betting odds shift in that direction.
-
- The fact that life arose early in Earth's history is an enormous factor in shifting the betting odds. If you go with the microfossil evidence, it gives you better than 3-to-1 betting odds that life arises commonly rather than rarely; if you use the evidence from zircon deposits, the betting odds increase to better than 9-to-1 that life is common rather than rare. If we re-ran Earth's history many times, we would expect life to arise often, rather than hardly at all.
-
- Deep under the sea, around hydrothermal vents, where no sunlight reaches, life still thrives on Earth. How to create life from non-life is one of the great open questions in science today, but if life can exist down there, perhaps undersea on Europa or Enceladus, there's life also?
-
- Deep under the sea, around hydrothermal vents, where no sunlight reaches, life still thrives. But the same procedure actually yields very little information about intelligent life. If you start with the same betting odds (50:50) for intelligent life, assuming that life has arisen, the Bayesian analysis slightly favors the rare-intelligence scenario. But the effect is slight, transforming the 1-to-1 betting odds into something that looks more like a 3-to-2 scenario, in favor of rarity.
-
- This does not mean that intelligent life is rare. It means that the information we have doesn't do a very good job of constraining whether intelligent life's emergence is rare or common.
-
- This is a stark contrast to the question of life's emergence at all: the data is good enough to conclude that the common-life scenario is more likely than the rare-life scenario. If we started with a clone of early Earth, life would likely emerge, but we cannot reach a good conclusion concerning the emergence of intelligent life.
-
- Intelligent aliens, if they exist in the galaxy or the Universe, might be detectable from a variety of signals: electromagnetic, from planet modification, or because they're spacefaring. But, we haven't found any evidence for an inhabited alien planet so far. We may truly be alone in the Universe, but the honest answer is we don't know enough about the relevant probability to say so.
-
- Venus and Mars, among other worlds in our Solar System, had their own tickets as well, and it's eminently possible that life emerged on all three worlds early on; it certainly did on Earth. Only on our world did life sustain and thrive, however, and eventually give rise to an intelligent species and a technologically advanced civilization.
-
- We cannot turn the clock back and see how things would have turned out, nor do we have techno-signature data or a surefire Earth-like exoplanet to help us understand these cosmic likelihoods.
-
- However, a clever analysis can reveal that when it comes times to place your bets, bet on life's emergence as a common occurrence as opposed to a rare one.
-
- For intelligence, however, the only information is a slight nudge in the rare direction. To learn anything more, we'll need data that we don't yet have. Stay tuned we have a lot more to learn. You are not alone in not understanding this. The best we can say is that it is what it is or you would not e reading this.
-
------------------------------ Other Reviews that tackle the question:
-
- 2426 - LIFE - Exploding stars create life , and destroy life. Our galaxy is big and mostly empty space, but it harbors millions of blackholes that are remnants of supernovas and collapsing stars. When a giant star burns all it’s fuel, no heat remains to create the pressure withstanding the compression of gravity. The force of gravity collapses the stars mass into a singularity at the center of a blackhole. These creators of life are every where.
-
- 2361 - How did life start on Earth? If geological processes somehow push particles into higher energy states they would naturally seek to return to their ground state. Maybe life is here to help nature solve nature’s energy problems. Living systems use chemical reactions to get down to lower energies. That is how living things work.
-
- 2288 - The diversity of life. Science has catalogued about 1,800,000 species that live on this Earth. But, what if I told you that represented only 1% of the life that lives here. It is true, 99% of life has not been identified and catalogued to date.
-
- 2166 - The evolution of life. Time lapse of the birth of the Universe to forever. The big picture details the time from the creation of the Universe to the death of the Universe. Because this time scale is so large, our existence here on Earth is a mere spec of time. In order to resolve human events in these Universal events the time has been magnified 10,000,000,000 times.
-
- 2148 - The Origins of Life in the Universe. Life is highly ordered and has low entropy. Life must operate far above thermodynamic equilibrium in order to stay alive. When we die entropy wins and we reach thermodynamic equilibrium in the grave. Life must continuously expend energy, metabolism, in order to avoid thermal equilibrium with the ground.
-
- 2122 - Are we alone in the Universe? Astronomers only started looking for alien life in the Universe 50 years ago. So far, we have not found any sign of alien life. Life is one thing but intelligent life is something else again. Intelligent life is even more unlikely on this tree of life and the evolution processes. If the Universe is infinite, the impossible will happen somewhere.
-
- 1942 - What is the earliest life on Earth? What is the earliest life on Earth? When did it first arrive? What was the environment that allowed life to evolve? Could the same environment allow life to evolve on other planets and moons? Enceladus and Europa for example?
-
- 1874 - Will we likely find life on exoplanets and exomoons? Over 3,000 exoplanets have been discovered. But, moons are the most likely first discoveries for life outside of Earth.
-
- 1809 - Life Beyond Earth? What is the likelihood and what would be the criteria to search for? Life has its dependencies, we can’t live without them.
-
- 1690 - Discovering life? If there is life on other planets we need to come up with ways our spacecraft explorers can detect it. If we find a life form beyond Earth we have new insight into the probability of life be ubiquitous throughout the Universe.
-
- 844 - Life on Other Planets. The early searches for life in our own solar system concentrated on the microbial life similar to what has existed on Earth for 4 billion years. When we go outside our solar system we change the strategy and search for intelligent life as well. Intelligent life on Earth has only been with us for a few million years. But, if we expand our search for intelligent life we may be able to find the signals that other intelligent beings use to communicate with each other.
-
- 813 - Life from Comets. To investigate “life” you need to know physics, chemistry, biology, and astronomy, let alone religion. Self-replicating cells are about the most complex things you can encounter in life. How did it get started? Science has tried to replicate early conditions on Earth in a bottle. They have added the atmosphere, the nutrients, and the electrical and thermal energy that represented early Earth. Sure enough, amino acids formed in the jar all by themselves. Amino acids are the building blocks of proteins essential for life. But, there are a lot of steps between chemistry and biology.
-
- 476 - Gamma Rays and Cosmic Rays
- 541 - Cosmic Rays
- 542 - Neutron Star Flare - Magnetar 1806-20
- 510 - Supernova you can see.
- 508 - You Are Made of Star Dust
- 504 - Accelerating Universe from Unknown Force.
- 455 - Supernovae - A Cosmos, Everything but Quiet. It is violent out there.
- 342 - The whole shebang. The Universe is under no obligation to make sense.
-
- May 23, 2020 2744
----------------------------------------------------------------------------------------
----- Comments appreciated and Pass it on to whomever is interested. ----
--- Some reviews are at: -------------- http://jdetrick.blogspot.com -----
-- email feedback, corrections, request for copies or Index of all reviews
--- to: ------ jamesdetrick@comcast.net ------ “Jim Detrick” -----------
- https://plus.google.com/u/0/ -- www.facebook.com -- www.twitter.com
--------------------- Saturday, May 23, 2020 -------------------------
-----------------------------------------------------------------------------------------
No comments:
Post a Comment