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12th April 2005, 07:35 AM
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Anyone that has done any gardening knows that a plant needs between 5 and 8 hours of sunlight a day. Depending on the plant. Also we know that every billion years we gain 4 hours per day. So three billion years ago, the day would be about 12 hours long and there would be only 6 hours of sunlight. I am wondering though, would there not still be the same amount of sunlight in a 24 hour period of time? Is not the length of the day compared to the lenght of night based more on the tilt of the planet compared to the spinrate? |
12th April 2005, 07:40 AM
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Reps: 5,749 (power: 18) | | Originally Posted by JohnR7 Anyone that has done any gardening knows that a plant needs between 5 and 8 hours of sunlight a day. Depending on the plant. Also we know that every billion years we gain 4 hours per day. So three billion years ago, the day would be about 12 hours long and there would be only 6 hours of sunlight. I am wondering though, would there not still be the same amount of sunlight in a 24 hour period of time?
Yes, on average 12 hours. Is not the length of the day compared to the lenght of night based more on the tilt of the planet compared to the spinrate?
Relative amounts of day and night in a given season depend upon the tilt. Actual lengths of each period depend on the spin rate. It'll still average 50% of the time over the year though.
But plants are a bit more complicated than that. They know not just how much light they're getting, but how long the photoperiod is. This tells them when to flower, seed and when to lay down bulbs or tubers for the winter. Obviously, plants' photoperiod responses have evolved over time to cope with the slow, gradual increase in average photoperiod over billions of years.
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12th April 2005, 10:05 AM
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12th April 2005, 10:13 AM
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Reps: 295,212,687,427,838,720 (power: 0) | | Originally Posted by JohnR7 Anyone that has done any gardening knows that a plant needs between 5 and 8 hours of sunlight a day. Depending on the plant. Also we know that every billion years we gain 4 hours per day. So three billion years ago, the day would be about 12 hours long and there would be only 6 hours of sunlight. I am wondering though, would there not still be the same amount of sunlight in a 24 hour period of time? Is not the length of the day compared to the lenght of night based more on the tilt of the planet compared to the spinrate?
Exactly. The day gets shorter, but so does the night. No matter how much faster the Earth was spinning, there's still 12 hours of each in a 24-hour cycle |
12th April 2005, 10:59 AM
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Reps: 4,042 (power: 12) | | Originally Posted by JohnR7 Anyone that has done any gardening knows that a plant needs between 5 and 8 hours of sunlight a day. Depending on the plant.
Modern plants require 5-8 hours a day, yes. In temperate areas. Then again, there are arctic plants that survive on a much leaner diet of light, including several species of lichen, moss, and tundra willows. Evolution has allowed plants to adapt to a whole range of environments. I imagine plants on early earth were hardier, and capable, like modern Arctic plants, of subsisting on less steady sunlight.
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12th April 2005, 11:56 AM
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12th April 2005, 01:04 PM
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12th April 2005, 02:28 PM
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Reps: 97 (power: 0) | | Originally Posted by Blackmarch If the earth did spin faster way back in the dino's day, that would help explain why animals were able to reach the sizes they did.
how so? |
12th April 2005, 02:59 PM
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The G-forces would probably stretch their bodies skyward  |
12th April 2005, 03:26 PM
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Reps: 97 (power: 0) | | | but surely that would make them long and thin... not big and bulky like dinosaurs.. | | |
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