The Loom

Set Your Watch

This image came out a couple months ago in Nature, but I just came across it today. I quite like the way it sums up the history of life–something that’s maddening hard to do, since the time scales are so vast. It shows how life’s diversity has been accumulating for billions of years. This chart shows the timing of the earliest paeolontological evidence for different kinds of life, ranging from fossils to chemical markers. A few definitions may help. Phototrophic bacteria can harness sunlight to grow. Cyanobacteria are also known as blue-green algae (aka pond scum). Eukaryotes are species such as amoebae, plants, fungi, and animals. Algal kindoms include red algae and green algae (closely related to land plants). Some of these bars may need to be pushed back in time when earlier evidence is discovered. Some studies on DNA suggests that a number of such “ghost lineages” remain to be discovered.

life%20scale%20400.jpg

Comments

  1. #1 Scott Belyea
    February 27, 2006

    I like this diagram a great deal, and it was well worth the few minutes I’ve just spent contemplating it. Time measured in “billions of years” is one item for which the descriptor “mind-boggling” is valid. Tough to grasp.

    It’s a variant on the “clock-face” representation of life on earth telescoped into a 24-hour day.

    Yes, yes, I know … the whole thing actually took **6** 24-hour days, right?? :-)

  2. #2 Apikoros
    February 27, 2006

    I agree that this figure is a neat and useful summary, but two things bother me just a little. I’m concerned that it might be too easily mis-understood, especially by schoolchildren. First, it places Humans at the top, the zero hour, as if the whole thing leads up to Us rather than to Now.

    Secondly, the picture of the Earth is placed such that the line radiating from the center toward the pinnacle of Human-ness leads right through the east coast of North America. Again, reinforcing smug Northeastern triumphalism. The illustrator wouldn’t be from Harvard, by any chance?

  3. #3 Robert Isaacs
    February 27, 2006

    What strikes me from this image is that the complexity of organisms seems to increase exponentially. The period from invertebrates to humans seems to be a very short period of time in the history of life on Earth.

    Ray Kurzweil talks about this at length in his various books.

  4. #4 UndergradChemist
    February 27, 2006

    I agree with the first point by Apikoros, since it also makes the diagram a little less clear, and implies that there is some sort of cycle that is going to occur. What happens, for example, when the bar for “now” hits the bar for “Earth started”? Is that supposed to be the projected end of the solar system? I seem to recall that earth’s lifespan is only 2/3′s done, not 3/4 as the diagram would imply.

    I do remember a biophysics professor drawing us a diagram and saying, “at this scale, it is depressing to see that life is mostly over and done (two thirds of it, at least).” Not that 2 billion more years is that short, but still…

  5. #5 dbpitt
    February 27, 2006

    I read a statistic that said if the Earth is 24 hours old, than humans will have been around for 2 seconds.

    Apikoros, it look more like it goes through the midwest, like from Lousisiana to Minnesota, than the northeast.

  6. #6 Janne
    February 28, 2006

    Isaacs: I’m not all that sure that, for instance, vertebrates really are all that much more complex than having multicellular structures in the first place – which in turn is not clearly more complex than the eucaryotic cell.

    I get the impression the early things took a whole lot of time because they really were very hard, and took some very big advancements to get where they are. Once you had those very complex building blocks, assembling them into macroscopic plants, mammals and so on is probably comparatively easy.

  7. #7 john
    February 28, 2006

    I too am deeply troubled and offended. The line going up to “Shelly Invertebrates” goes right through the West Coast and I live in Los Angeles. So dehumanizing…

  8. #8 rcap
    February 28, 2006

    Carl… The soft blue shell that wraps three-fourths of the planet– “Life” as it is so designated– what is this? The distance from the “origin of Life” to phototropic bacteria implies some fundament not of the Kingdom of Bacteria? Or is Bacteria so robust a presence & so notable a progeniture it merits two shells? (not that I would disagree…)

    As an aside, I look forward to the day when some clever graphic artist can impress upon us the extraordinary “shedding of Life” (populations & individuals) & the resultant depositions (such as the tissue of potent soils) that have contributed to this equivocal determinism evoked by the above wheel’s “advance of Life” (because in 3 dimensions it is a spiral).

  9. #9 Monte Davis
    February 28, 2006

    I lean toward Janne’s position and away from “exponentialism,” which seems to me a product of tunnel vision. We’re still far from consensus on the best metric for complexity, but IMO the difference between, say, a lipid droplet and a eukaryotic cell is greater than that between the cell and a vertebrate.

    From this POV, a question such as “why did the Cambrian explosion come so late?” dissolves: it took 4 billion years to do the hard part of accumulating all those interlocking biochemical hypercycles (including the genetic ones — homeobox etc — and little matters such as pumping O2 into the atmosphere). Once that was done, it was an easy 500-million-year jog to beetles, sequoias, blue whales, thee and me.

  10. #10 Andrés Moreira
    February 28, 2006

    Hum. I would like someone with good knowledge of taxonomy and biomass figures to do something similar. It would be nice, for instance, to set the width of the coloured archs to show the biomass percentage. And it would be also nice to divide the rainbow evenly between the realms and main clades of the tree of life. As it is, the image is quite anthropocentric, defining as “important” the steps that helped us become us (they did remember plants, though). And that may be a reason for its exponential feeling. Nice image anyway (even if my home town in Southamerica marks the amazing invention of cyanobacteria).

  11. #11 Jimmy
    February 28, 2006

    Do the different levels in the diagram correlate to geologic strata?

  12. #12 David B. Benson
    February 28, 2006

    No, the levels in the diagram do not ‘correspond’ to geological strata. Of course, the higher the diagram level, the higher the geological strata with the evidence. But in general there will be many different geological layers before the next jump in this diagram.

  13. #13 Don
    March 1, 2006

    I like the football field analogy. You start across it at one goal line, and every step you take is millions of years. Out at the 25 yard line life begins. Not till you’ve walked farther than 80 yards, inside the other 20 yard line, do the dinosaurs show up. You’re inside the 5 yard line before mammals appear. First hominids well inside the 1 yard line, in fact quite near 1 inch from the goal line. And the entire existence of modern humans is in the mere thickness of the last blade of grass at the goal line.

    If you want to consider the earth has another 4 billion years ahead of it you could compact the whole thing to the first 50 yards, and humans have been around for 1/2 the thickness of the last blade of grass before midfield. 50 more yards to go.

  14. #14 luca
    March 1, 2006

    Pretty concise diagram, so much better of the other I’ve seen on the subject. But I, as from comment #4, am worried about the cyclicity that the round shape of the Earth suggests. I wonder what kind of weird idea could creationist get out of this…

  15. #15 Jeff
    March 1, 2006

    I’m hung up on the colored bands, and what they represent. They certainly don’t repesent major groups of organisms because that would mean vertebrates (dark red bar) aren’t represented until mammals came along.

    Therefore, I’m led to believe that the indicated milestones are great leaps in diversity and the adding of a bar is simply quantitative. However, I would argue that the rise of mammals doesn’t really imply an increase in diversity since it appeared as if mammal diversity was replacing dionsaur diversity.