There's more to life on earth than its ability to sustain liquid water.
Earth is often referred to as a Goldilocks planet. This has traditionally been connected to Earth's proximity to the sun allowing liquid water to exist on its surface. In fact, that assumption and some others led to something called the Drake Equation developed in Greenbank, West Virginia in 1961. It was a complex equation that calculated the number of planets in orbit around a star at the ideal distance for the sustained existence of intelligent life. The number of planets postulated based from the Drake Equation were 1000 to 100,000,000 in the Milky Way galaxy. More recent data from Kepler has put the estimate to around 12-17 billion Earth like planets in the Milky Way.
It may be true that billions of planets or more are in this "Goldilocks" orbit but what kind of life are we talking about and how are we defining intelligence? Bacterial, single-celled organisms or complex and diverse organisms with cognitive intelligence? In order for an advanced species to evolve and emerge as an intelligent, cognitive being such as humans - numerous other Goldilocks factors need to occur. It's not just about the water. Fortunately for us, we have that advantage. Here are the top 15 Goldilocks factors that make life on Earth as we know it possible.
Image by Nasa.gov
1. Proximity to the Sun allowing liquid water.
This is essentially the greens-fee for any form of life in the universe. Yes, it's possible that life can exist without water but those ideas are purely theoretical and no empirical evidence exists to support the assumption.
2. The size and composition of Earth as a Rocky Planet
Given some recent studies of distant stars and the on-going discovery of exoplanets, many planets in the universe appear to be gas-giants similar to Saturn, Jupiter, Uranus and Neptune. While there are also theories to imagine life on gas planets, the current science indicates that a rocky planet offers the best foundation for life and especially the diversity of life.
3. Stability of Earth's atmosphere and chemical composition.
An atmosphere appears to be critical to life whether it be a gaseous atmosphere on the surface of the planet, or a saturated atmosphere such as the Earth's oceans, seas, lakes and rivers. The chemical composition and density is also important. Mars has a very thin atmosphere and the ability of an organism to derive sustenance from the scant molecules is one of the factors that makes abundant life on Mars problematic. Not so on earth. Our atmosphere is rich in Nitrogen, Carbon Dioxide, Oxygen and other compounds that create a benign atmospheric combination.
4. The Magnetosphere.
Image by NASA
The fact that Earth has a metallic, molten core creates a magnetic field around the planet called the Magnetosphere. This invisible "gravity shield" deflects radiation from the sun and space and protects organisms on the planet from the solar wind. Mars was once a highly volcanic planet (an indication of a molten core), but its volcanoes have long-since become dormant and it appears to have a very weak and fluctuating Magnetosphere. This may be why its atmosphere is virtually non-existent. The solar wind simply stripped it away without the protection of a strong and steady Magnetosphere.
5. Consistency of temperatures on Earth.
The average temperature on Venus is 462°C (864°F). On Mars it’s -60°C. (-80°F). Earth's temperature average is 15°C. (59°F). The average temperature on Earth not only allows liquid water to exist, but also provides a relatively stable environment for organisms. Temperature extremes limit diversity of biological life forms, and while some bacteria can survive extremes, advanced organisms typically are too complex to endure the extremes.
6. Diversity of Life.
Copyright (c) 2004 Richard Ling
The Diversity of life on Earth has two unique advantages. For one it creates a food-chain that can sustain a variety of species allowing for greater evolutionary development. This is important given the statistical inevitability of catastrophic events on any planet. In fact, the diversity of life on Earth may be the only reason life on Earth has continued after the extinction of 65% of all species including the dinosaurs 65 million years ago due to an asteroid impact, and nearly 95% of all species 250 million years ago due to a massive series of volcanic eruptions across what is now Siberia.
7. Earth's moon.
Our moon has a remarkable, stabilizing affect on our planet. Without the moon, the rotation of the Earth would result in a day that averages about 4 hours. The moon has slowed us down to a comfortable 24 hours and has also stabilized Earth's rotation on its axis. The moon also creates tides which is believed to have created an evolution machine in the tide-pools and tidal-zone between land and sea. This repeated tidal action is thought to have encouraged evolution as animals on the shore slowly became accustomed to a daily land and sea environment allowing them ultimately emerge onto the land.
8. Stability of the Sun as a star.
Our sun is actually a very average star in terms of size and activity. That's a good thing. That means the radiant heat and radiation is typically consistent although occasional solar flares do show up to send out bursts of radiation. Fortunately we have survived those rare bursts for thousands of years. Our sun is also a solitary star. It's believed that 85% of stars in the Milky Way are binary stars. It's interesting to think about two stars orbiting each other, but for planets in a solar system the gravitational forces would wreck havoc on the planets and probably cast asteroids and comets around like shot from a shotgun.
9. The Ozone Layer.
Image by NASA
We hear about the Ozone layer all the time. In fact, we now know there are recurring holes in the Ozone at the north and south poles. Ozone is much like the Magnetosphere. It's another buffer against solar radiation especially Ultra-violet (UV) radiation and is another result of our dense and complex atmosphere. Even though many planets may have a robust and dense atmosphere, the existence of an Ozone layer and the function it performs as a radiation shield is most likely rare and unique.
10. The amount of water on earth.
Water on a planet is a great way to give life a head start. But you need more than a puddle. Some theories postulate that the water on earth was largely due to icy, comet collisions during the late heavy-bombardment 3.3 to 4.5 million years ago. The result was essentially a water planet with less land than sea. If water is the wellspring of life, Earth has more than enough.
11. Jupiter as a Solar System vacuum cleaner for asteroids, comets, and meteors.
Astronomers watched in amazement as the comet Shoemaker-Levy broke into 9 pieces and slammed into Jupiter in 1994. The impact on the planet was frightening and a reminder of Jupiter's value in our Solar System. In many respects, its immense gravitational field acts like a system wide vacuum cleaner attracting rogue asteroids, comets and meteors to its surface and away from other planets including Earth.
12. The stability of the solar system.
3.3 to 4.5 millions years ago, our Solar System was a highly unstable environment. The orbits of the gas giants on the outer rim of our Solar System were closer and not as concentric resulting in a maelstrom of rocky debris and icy comets in constant collision across the planets. Any life at that time didn't stand a chance beyond the most resilient and buried bacteria. No doubt, there are millions and millions of solar systems enduring the same. Fortunately, our Solar System is relatively stabilized in terms of planetary orbits.
13. Our location in the Milky Way Galaxy
The galactic habitable zone. Image by NASA
Our location in the Galaxy is at the edge of a spiral arm called the Orion Arm, and is about two-thirds of the way from the center of our galaxy to the edge of the starlight. That's a very good place to be. Stars and systems closer to the center of the Milky Way are in a very crowded neighbourhood where collisions with celestial bodies and high radiation exposure is statistically higher. There's also the affect of that super-massive black hole at the center of our galaxy. Our location is a very good one that once again provides relative stability and safety.
14. The Stability of the Galaxy.
Yes, galaxies matter too. Many galaxies are in collision. In fact, the Milky Way galaxy is on a collision course with the much larger Andromeda galaxy in about 3 billion years. The Milky Way galaxy is also rather small compared to some of the giants that occupy the universe. This too could decrease the odds of dramatic and cataclysmic events that might take place in a dense, massive galaxy.
15. The Stability of our Quantum Universe
No one thinks about this much, but there is a theory that parallel universes exist. There are 4 levels of parallel universe and some of them would result in very strange places indeed. Our quantum universe seems apparently stable with firm laws of motion, energy, matter and gravity consistently applied across the universe. It may seem far-fetched but in addition to every other factor we may also be living in a Goldilocks universe.
Now have a look at what happens when things aren’t so serene. Here is the Top 5 Best and Most Interesting Exoplanets.
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