Constraining astronomical models with geological data

就像树木的年轮可以用来计算过去的天文年数，古老的珊瑚生长年轮可以用来估计过去一年的天数一样，未受干扰的沉积岩层可以潜在地记录地球和其他行星轨道结构的周期性变化。这些天文变化影响到通过气候系统（如冰期）过滤的大气顶部接收到的阳光量，这最终影响到沉积在深海等地的沉积物的数量和类型。这些天文参数的变化：地球的偏心率、倾角（倾斜）和气候岁差（自转轴类似于陀螺旋转的摆动），发生在数千年到数十万年的时间尺度上。通过国际海洋钻探项目（Ocean Drilling Program），深海中必要的地质记录直到最近才得以获得，该项目从海底数百米深的几公里深的水域中恢复沉积物岩心。然而，尽管我们预计每年的季节变化非常有规律，但以内行星为主的太阳系结构在数百万年的时间尺度上就不那么规律了——它已经被证明是“混乱的”。这意味着不可能无限期地计算诸如地轴倾斜的变化等方面。这阻碍了地质学家利用这些变化作为“节拍器”或节拍器来估计时间的努力。本研究的目的是利用沉积记录中的特征模式来提取天文参数，这些参数可用于延长模型计算有效的时间尺度。这是很重要的，因为它可以约束基本的物理参数，否则天文学家无法获得这些参数。更具体地说，我们希望从过去3000万到5000万年间的深海沉积物数据中找到几个不同的混沌行为，在极端情况下，甚至可以让天文学家非常准确地检验爱因斯坦广义相对论的预言。这里提出的研究将通过天文学家和地球科学家之间的新颖合作来完成。我们提出的研究的另一个目的是限制天文地球模型的演变：由于海洋中的耗散潮汐，地球的固体部分，月球和太阳，以及地球上质量的重新分配，例如冰河时代和地幔对流，地球的自转正在改变，并且通常随着时间的推移而减慢。由于能量守恒，这一过程也导致地球和月球之间的距离增加，目前每年几厘米。为了准确地计算太阳系，特别是地球的轨道结构和变化，限制地球过去自转变化的强度是很重要的。同样，正如树木年轮可以提供有关干旱和潮湿年份的信息一样，沉积物中记录的气候指标的详细模式可以用来提取过去地球模型的参数。我们现在可以使用新获得的沉积物岩心和额外的测量，为天文学家获得重要的信息。

Just as tree rings can be used to count astronomical years back into the past, and ancient coral growth rings can be used to estimate the number of days per year in the past, layers of undisturbed sedimentary rocks can potentially record cyclical variations in the orbital configuration of Earth and other planets. These astronomical variations affect the amount of sunshine received at the top of the atmosphere, filtered through the climate system (e.g. ice ages), which finally influences the amount and type of sediment deposited in, e.g., the deep sea. Changes of these astronomical parameters: the Earth's eccentricity, obliquity (tilt), and climatic precession (wobble of the spin axis similar to a spinning top), occur on time scales of thousands to hundreds of thousands of years. The necessary geological records from the deep sea have only recently become available through the international Ocean Drilling Program, which recovers sediment cores from hundreds of metres below the sea bed in waters several kilometers deep. However, although we expect seasons to change very regularly every year, the solar system configuration of predominantly the inner planets is less regular on time scales of millions of years - it has been shown that it is 'chaotic'. This means that it is not possible to calculate aspects such as the changing tilt of the Earth's axis back in time indefinitely. This hinders geologist's efforts to use these changes as 'metronome' or pace-maker to estimate time. The aim of this research is to use characteristic patterns in the sedimentary record to extract astronomical parameters that can be used to extend the time scale over which model calculations are valid. This is important in order to constrain basic physical parameters that cannot be obtained otherwise by astronomers. More specifically, we hope to find several distinct occurrences of chaotic behaviour from deep sea sediment data during the past 30-50 million years that, in the extreme case, would even allow astronomers to very accurately test the predictions of Einstein's general relativity. The research proposed here would be accomplished through a novel collaboration between astronomers and Earth scientists. One additional aim of our proposed research is to constrain the evolution of the astronomical Earth model: due to the dissipative tides in the oceans, the solid parts of the Earth, Moon and Sun, as well as redistribution of mass on Earth due to, e.g. ice-ages and mantle convection, the rotation of the Earth is changing, and generally slowing down with time. Due to conservation of energy, this process also results in an increasing distance between the Earth and Moon, currently a few centimetres per year. In order to accurately calculate the orbital configuration and variations of the solar system, and the Earth in particular, it is important to constrain how strong this change in the Earth's rotation has been in the past. Again, just as tree rings can give information about dry and humid years, the detailed pattern of climate indicators recorded in sediments can be used to extract parameters of the Earth model in the past. We can now use newly available sediment cores, and additional measurements, to obtain important information for astronomers.