Although it seems a long way from interstellar space, the early Earth is a fascinating laboratory for life’s development that should yield clues about how life takes hold elsewhere. Thus new work on the movements of the early continents catches the eye. In this case, the Gondwana supercontinent is found to have undergone a 60-degree rotation across Earth’s surface during a highly interesting period, the Early Cambrian. This is the fecund era when the major groups of complex animals appeared in relatively rapid succession.
Gondwana is what we can call the southern precursor supercontinent, a vast region that would eventually separate from Laurasia roughly 200 million years ago when the Pangaea supercontinent broke into two large areas. This Wikipedia article gives you the basics on Gondwana, noting that it included most of the landmass in today’s southern hemisphere, including Antarctica, South America, Africa, Madagascar, Australia, New Guinea and New Zealand, along with the Indian subcontinent and Arabia (although the latter two have, obviously, moved into the northern hemisphere).
Image: The paleomagnetic record from the Amadeus Basin in Australia (marked by the star) indicates a large shift in some parts of the Gondwana supercontinent relative to the South Pole. Credit: Ross Mitchell/Yale University.
The movement of the entire Gondwana landmass was relatively rapid, with some regions attaining a speed of at least 16 (+12/-8) centimeters per year about 525 million years ago. Compare that with the pace of today’s shifts, which are no higher than 4 centimeters per year. The intriguing question is whether the shift results from plate tectonics — the continental plates in motion with respect to each other — or ‘true polar wander,’ which involves the solid land mass down to the liquid outer core rotating together with respect to the planet’s rotational axis, changing the location of the geographic poles. More in this Yale University news release.
What study author Ross Mitchell (Yale University) found is that true polar wander is the most likely scenario, the rates of Gondwana’s motion exceeding those of plate tectonics of the past few hundred million years. But arguments about polar wander vs. plate tectonics are ongoing and have been for decades. Mitchell can only say “If true polar wander caused the shift, that makes sense. If the shift was due to plate tectonics, we’d have to come up with some pretty novel explanations.”
But back to the main issue, which is the effect such migration would have had on the environment and living creatures. In this model, Brazil shifted from close to the south pole toward the tropics, the kind of movement that would have affected carbon concentrations and ocean levels. Here’s what Mitchell has to say about the results:
“There were dramatic environmental changes taking place during the Early Cambrian, right at the same time as Gondwana was undergoing this massive shift. Apart from our understanding of plate tectonics and true polar wander, this could have had huge implications for the Cambrian explosion of animal life at that time.”
It will be fascinating to see how this work is followed up in other locales as we work to explain the shift’s effects. Mitchell and team did their work studying the magnetization of ancient rock in the Amadeus Basin of central Australia. The paper is Mitchell et al., “Rapid Early Cambrian Rotation of Gondwana,” in Geology Vol. 38, No. 8 (August, 2010), pp. 755-758 (abstract).
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There are a number of youtube etc. animations showing continental drift, but this one also shows associated biological developments:
What an incredible world we live in…
Huh, I hadn’t realised the Gondwana supercontinent existed both before and after Pangaea. Sixty degrees is quite impressive for true polar wander, maybe there are some implications here for the potential habitability of high-obliquity planets?
Water Deep in Earth Key to Survival of Oldest Continents
“Why do we still find rocks from the Archean, one of the earliest geological eons on Earth dating from about 3.8 to 2.5 billion years ago? This is an apt question as our planet is one of the most dynamic in the solar system. Earth’s crust has been constantly destroyed and created throughout its 4.5-billion-year history.”
The Earth Doesn’t Care
About what is done to or for it.
The cover of The American Scholar quarterly carries an impertinent assertion: “The Earth Doesn’t Care if You Drive a Hybrid.” The essay inside is titled “What the Earth Knows.”
What it knows, according to Robert B. Laughlin, co-winner of the 1998 Nobel Prize in Physics, is this: What humans do to, and ostensibly for, the earth does not matter in the long run, and the long run is what matters to the earth. We must, Laughlin says, think about the earth’s past in terms of geologic time.
For example: The world’s total precipitation in a year is about one meter—“the height of a golden retriever.” About 200 meters—the height of the Hoover Dam—have fallen on earth since the Industrial Revolution. Since the Ice Age ended, enough rain has fallen to fill all the oceans four times; since the dinosaurs died, rainfall has been sufficient to fill the oceans 20,000 times. Yet the amount of water on earth probably hasn’t changed significantly over geologic time.
Damaging this old earth is, Laughlin says, “easier to imagine than it is to accomplish.” There have been mass volcanic explosions, meteor impacts, “and all manner of other abuses greater than anything people could inflict, and it’s still here. It’s a survivor.”
Full article here:
The Origins of Life
A mineralogist believes he’s discovered how life’s early building blocks connected four billion years ago.
By Helen Fields
Photographs by Amanda Lucidon
Smithsonian magazine, October 2010
Full article here:
Earth’s continents from 600 million years ago to 100 million years from now:
To tie this into interstellar travel, the Voyager Records have a depiction of our planet’s continents in the past, present, and future:
This was based on the plaque Carl Sagan designed for the LAGEOS satellite that was launched in 1976 and will remain in Earth orbit for 8 million years:
And that design originally came from a diagram in the 1966 Time-Life Science book Planets, which Sagan was editor of.
Faint Young Sun Paradox Not Solved, Says NASA
Last year, scientists claimed to have solved the faint young Sun paradox. They were wrong. Now the paradox is back and more puzzling than ever.
Liquid water has flowed on Earth for some 3.8 billion years, since not long after the planet formed. The evidence comes from rocks that date from that period which seem to have formed under the action of water.
But this presents palaeontologists and geologists with a problem. At that time, the Sun was some 30 per cent dimmer than it is today and would not have provided enough heat to keep water liquid on the surface.
This is known as the faint young Sun paradox and it has puzzled scientists since the 1970s when astronomers first pointed it out. But it didn’t really worry anybody. The obvious solutions are that the Earth was warmer because it reflected less heat from the Sun, it had a lower albedo, or that it was victim of a runaway greenhouse effect. One of these must be right but nobody was sure which.
But last year, a group of researchers claimed to have solved the paradox. They said that the make up of rocks from that time exclude the possibility that the atmosphere was rich in a greenhouse gas such as methane or carbon dioxide.
Instead, the Earth must have had a lower albedo and therefore must have absorbed more heat from the Sun than it does today. The lower albedo, they argued, was the result of fewer biological particles in the atmosphere. These nucleate water droplet formation. So without them there would be fewer clouds and less sunlight reflected into space.
These guys published their solution in Nature and the problem was thought to have been solved. (We looked at another mechanism that may have prevented cloud formation in the early atmosphere about a year ago.)
But today Colin Goldlatt and Kevin Zahnle at NASA’s Ames Research Center in Moffett Field re-ignite the controversy.
They’ve looked at this problem again and studied the effect of fewer clouds. They say that however you do the numbers, this could not have made the Earth hot enough to allow the existence of liquid water.
Clouds have two effects. In general, high clouds trap heat while low clouds reflect it. “Therefore the absolute upper bound on warming by decreasing cloud reﬂectivity would be found by removing low clouds entirely,” they say.
When you do that in a computer model of the Earth’s early climate, you get no more than half the heating necessary to maintain liquid water on the surface.
“We show that, even with the strongest plausible assumptions, reducing cloud and surface albedos falls short by a factor of two of resolving the paradox,” say Goldlatt and Zahnle.
So the paradox is alive and well; and more puzzling than ever. Last year we discovered that a greenhouse effect can’t explain the paradox. Now we know that a lower albedo wouldn’t have done the trick either.
So the race is back on to nail this problem once and for all. Get your thinking caps on.
Ref: http://arxiv.org/abs/1105.5425: Faint Young Sun Paradox Remains
Tiny Tracks of First Complex Animal Life Discovered
Jeanna Bryner, LiveScience Managing Editor
Date: 28 June 2012 Time: 02:14 PM ET
A teensy sluglike animal that wriggled around the sediment in search of food at least 585 million years ago didn’t die in vain. The tiny mover left behind tracks that researchers now say represent evidence of the earliest known bilateral animal, or multicellular life with bilateral symmetry.
The finding, detailed in the June 29 issue of the journal Science, pushes back the date for the existence of advanced multicellular animal life by at least 30 million years. The oldest evidence before this discovery came from Russia and dated to 555 million years ago.
Geologists Ernesto Pecoits and Natalie Aubet of the University of Alberta in Canada were studying the rocks at a site in Uruguay in 2007 when they discovered the tracks. They saw that the tracks had been made by a bilaterian, or an animal with bilateral symmetry, with a front and back as well as a top and bottom, unlike corals and sponges. (Tiny sea sponges date back at least 635 million years.)
Full article here:
Life Before Earth
Alexei A. Sharov, Richard Gordon
(Submitted on 28 Mar 2013)
An extrapolation of the genetic complexity of organisms to earlier times suggests that life began before the Earth was formed. Life may have started from systems with single heritable elements that are functionally equivalent to a nucleotide.
The genetic complexity, roughly measured by the number of non-redundant functional nucleotides, is expected to have grown exponentially due to several positive feedback factors: gene cooperation, duplication of genes with their subsequent specialization, and emergence of novel functional niches associated with existing genes. Linear regression of genetic complexity on a log scale extrapolated back to just one base pair suggests the time of the origin of life 9.7 billion years ago.
This cosmic time scale for the evolution of life has important consequences: life took ca. 5 billion years to reach the complexity of bacteria; the environments in which life originated and evolved to the prokaryote stage may have been quite different from those envisaged on Earth; there was no intelligent life in our universe prior to the origin of Earth, thus Earth could not have been deliberately seeded with life by intelligent aliens; Earth was seeded by panspermia; experimental replication of the origin of life from scratch may have to emulate many cumulative rare events; and the Drake equation for guesstimating the number of civilizations in the universe is likely wrong, as intelligent life has just begun appearing in our universe.
Evolution of advanced organisms has accelerated via development of additional information-processing systems: epigenetic memory, primitive mind, multicellular brain, language, books, computers, and Internet. As a result the doubling time of complexity has reached ca. 20 years. Finally, we discuss the issue of the predicted technological singularity and give a biosemiotics perspective on the increase of complexity.
Comments: 26 pages, 3 figures
Subjects: General Physics (physics.gen-ph)
Cite as: arXiv:1304.3381 [physics.gen-ph]
(or arXiv:1304.3381v1 [physics.gen-ph] for this version)
From: Alexei Sharov [view email]
[v1] Thu, 28 Mar 2013 17:00:11 GMT (287kb)