Distribution of landmasses of the Paleo-Earth
Post date: Jul 06, 2011 3:35:40 PM
Our planet shows different features as it rotates along its axis, sometimes dominated by land and others by ocean. Land areas are distributed predominantly in the Northern Hemisphere (68%) relative to the Southern Hemisphere (32%) as divided by the equator. Coincidentally, the same can be say about the East-West distribution with most in the Eastern Hemisphere (68%) relative to the Western Hemisphere (32%). These hemispheres are divided by an imaginary circle crossing -20° longitude (20°W), which makes the Eastern Hemisphere center at 73° longitude (73°E). As Earth evolved through time these numbers changed dramatically.
If we focus on East-West areas, two distinctive interpretations can be defined: the side associated with more continental area, the Maximum Facing Area (MFA), and the side associated with more apparent (normal) area, the Maximum Normal Area (MNA). The MFA is sort of East-West hemisphere area division while the MNA is based on the apparent viewable area as a disk. In practice, the longitudinal location of the MFA and MNA are close, but not necessarily the same.
The MFA is normalized based of the total continental area available in the planet while the MNA is normalized to the total area of the disk (without prior knowledge of the global land area). For example, a MFA of 68% means that 68% of the land area is in one side of the planet, while a MNA of 42% means that up to 42% of the planet's disk area is covered by land at any moment. Therefore, the MNA is somewhat related to the maximum diurnal albedo of the planet as land areas are usually brighter than ocean areas, although clouds tent to minimize the effect.
Table 1 shows the North-South and East-West analysis of the land areas of Earth's past derived from our Visible Paleo-Earth project datasets. Figure 1 shows the hemisphere of Earth with more apparent area (MNA) in the last 750 million years (the actual longitude value of this side is show in the last column of Table 1). Figure 2 shows the full analysis for current Earth, other periods and further analysis of Table 1 results are available here (some of the previous values were slightly corrected in Table 1). We are using the curves of the Normal Area (i.e. Figure 1, c) to correlate Earth's albedo with land areas, a procedure that will be important to interpret future light curves from Earth-like exoplanets.
Table 1. Distribution of land areas of Earth in the last 750 million years. The global land coverage varied little within 10 to 30%, however, there where large transitions from South to North (Late Triassic, 220 Mya) and from East to West (Early Devonian, 400 Mya). Also, note the extreme clustering of over 95% of the land areas in one side of the planet (MFA) during Pangea (Middle Triassic, 240 Mya) and Rodinia (Precambrian, 750 Mya).
Figure 1. Earth showing the side with more continental area (MNA) in the last 750 million years.
Figure 2. Distribution of land areas of Earth today. The figures are divided in four frames, a context paleomap in an equirectangular projection with annotated percent coverage of ocean and lands areas, including how the land is divided between the northern and southern hemisphere (a), the latitudinal distribution of land areas every 15 degrees (b), the viewable land Facing Area (top curve) and Normal Area (bottom curve) as a function of longitude (c), and the longitudinal distribution of land areas every 30 degrees (d).