Such “hyperthermal” events periodically come and go throughout Earth’s history, but this one was particularly intense for unclear reasons. Crocodiles basked on Arctic beaches lined with palm trees, and steamy swamps and jungles stretched across much of the midlatitudes. In a span of scarcely 20,000 years-not even a rounding error in most measures of geologic time-massive amounts of carbon dioxide flowed into the atmosphere, and average temperatures rose by five to eight degrees Celsius. The torque is then this multipled by $a$ and if assumed constant over billions of years would decrease the angular momentum of the Earth's orbit by 1 part in a billion - so this can safely be neglected.Some 56 million years ago, during the transition between the Paleocene and Eocene epochs, Earth caught a fever. The drag force is about $0.5 \rho v^2 \pi R^2$, where $v$ is the velocity of Earth's orbit and $\pi R^2$ is the cross-sectional area presented by the Earth. A review by Guedel (2007) suggests a mass loss rate over the last 4.5 billion years that increases as $t^$. It seems, from observations of younger solar analogues, that the mass loss from the early Sun was much greater than the modest rate at which it loses mass now via the solar wind (or by solar radiation). Given that (a) probably happened sometime in the first tens of millions of years and likely did not alter the Earth's angular momentum greatly - it depends on the speed, mass and direction of the impactor and the amount of mass lost from the Earth-Moon system - I will ignore it. Of these I think only (a) (in the early lifetime of the Earth) and (b) (again, mainly in the first hundred million years or so, but with some effect afterwards) are important. Further possibilities are: (c) Tidal torques from the Sun have increased the angular momentum of the Earth (d) Radiation pressure from the Sun changes the orbit (e) drag from the interplanetary medium slows the Earth. Two events have certainly changed the Earth's orbital period (a) whatever collision formed the Moon and (b) the continuous process of mass loss from the Sun. What governs the Earth's orbital period is its orbital angular momentum and the mass of the Sun. I also found this article, but it seems more theoretical than evidence based. footnote, I've still not been able to find that article but it occurs to me, it could have been counting shorter days, not longer years - so, take that part with a grain of salt.Īre there any good studies out there on how many 24 hour days were in a year, 100, 300, 500, 800 million years ago? or 1 or 2 billion years ago? Either geological or orbital modeling? Preferably something a layman can read, not something written by and for PHDs? I remember reading some geological evidence that a year used to be longer, implying that the Earth used to be farther form the Sun, but I've since been unable to find that article, and for purposes of this question, lets count a day as 24 hours even though a day used to be quite a bit shorter hundreds of millions or billions of years ago. Is there any pretty good evidence on how the Earth's orbit has changed over time. ArticleĪnd Uranus and Neptune may have switched spots Article First, I know that modeling orbital mechanics of 8 planets is hard, but there are some theories out there, for example, Jupiter is thought to have moved in towards the sun then started moving away.
0 Comments
Leave a Reply. |