Freeze and evolve

01/07/2010

Updating The Chilling Stars and Magic Universe

When cosmic rays freeze the world, you’d better evolve

2100 million year-old multicellular fossil found in Gabon. Image: Kaksonen CNRS

Transforming the story of life on the Earth is a report in Nature today about multicellular creatures more than 2 billion years old, at a time when single-celled bacteria supposedly reigned supreme. Fossils you can pick up with your fingers, found in Gabon, West Africa, are far, far older than the multicellular animals that become detectable about 600 million years ago (Ediacaran period) and conspicuous 542 million years in the “Cambrian explosion”. The age is fixed with remarkable precision at 2070 to 2130 million years.

Exterior and interior of a fossil imaged by micro-tomography. Image: El Albani & Mazurier, CNRS

A team of 21 experts from France, Sweden, Denmark, Canada, Germany and Belgium make the report. The lead author is Abderrazak El Albani, at the University of Poitiers, France. He tells Agence France Press that “More than 250 specimens have been found so far. They have different body shapes, and vary in size from one to 12 centimetres.”

What excites me about the discovery is that here was a far-reaching evolutionary response to the rise of oxygen in the Earth’s atmosphere beginning more than 2000 million years ago. It occurred in the aftermath of a planet-wide freeze for which there is a cosmic explanation.

Chapter 6 in The Chilling Stars includes the story of “Snowball Earth” events. Here are some extracts.

In 1986, George Williams and Brian Embleton in Australia used the magnetism in grains of iron oxide dropped from ancient ice to show that they were released within a few degrees of the Equator. A few years later, Joseph Kirschvink of the California Institute of Technology confirmed this result in magnetism associated with other rock formations in Australia produced by ice action, and well dated as 700 million years old. He called it ‘bullet-proof evidence’.

It now seems clear that these extensive, sea-level deposits … were formed by widespread continental glaciers which were within a few degrees of the equator. The data are difficult to interpret in any fashion other than that of a widespread, equatorial glaciation.”

Kirschvink invented the name Snowball Earth for that dire climatic state. You have to visualise ice sheets, glaciers and frozen seas even at the Equator itself. The degree of ocean freezing is still debated. Some investigators imagine vistas of ice a kilometre thick or more, others prefer a ‘slushball’picture with drifting sea ice and icebergs. Either way the impact on life was severe.

Evidence from all the world’s continents unpacks into about three separate snowball episodes in the interval 750 to 580 million years ago. Worms that survived by scavenging the sea-bed detritus evolved the body-plans that made possible the explosion of animal life mentioned in the previous chapter, when the world became reliably warmer again in the Cambrian Period that started 542 million years ago.

Those cold Neo-Proterozoic times, as geologists call them, were not the only occasion of such radical events involving ice and evolution. By the end of the 20th century, geologists had amassed evidence from South Africa, Canada and Finland that confirmed two Snowball Earth episodes between 2,400 and 2,200 million years ago, in Palaeo-Proterozoic times. Our planet was then only half its present age.

Read the rest of this entry »


Star positions matter

18/06/2010

Updating The Chilling Stars

Why star positions matter for climate physics

The Making of History’s Greatest Star Map is an excellent account of the European Space Agency’s Hipparcos mission by the project scientist, Michael Perryman. It brings back vivid recollections:

  • of dismay after the launch in 1989, when the satellite failed to go into the right orbit and frantic steps were needed to improvise a survivable orbit and re-configure the observing programme.
  • of satisfaction when operations continued despite unplanned exposure to the Earth’s radiation belts, as well as some nasty solar flares, until the radiation damage became fatal in 1993.
  • of the appetizer in 1994, when early results of the Hipparcos star mapping helped in accurate prediction of the impacts of the fragmented Comet Shoemaker-Levy 9 on the planet Jupiter.
  • of joy on Isola di San Giorgo, Venice, in 1997 when the Hipparcos science team announced their first large-scale results, after a huge computational effort.

Hipparcos in an ESA impression

Astrometry took that great leap forward 30 years after Pierre Lacroute of the Strasbourg Observatory first proposed a space mission to measure the positions of stars, 20 years after Erik Høg of the Copenhagen Observatory refined the concept, and 17 years after ESA earmarked it as something to do. Ground-based astrometry had stalled, because of imprecisions due the turbulence of the atmosphere, and its remaining aficionados had little lobbying power. As a result, Hipparcos remained a distinctly European space project – the first in which there was no competition with the US or Soviet space science programmes.

Applications of the Hipparcos Catalogue of 100,000 plus stars and the Tycho 2 Catalogue with 2.5 million stars (to a lesser but still unprecedented accuracy) have ranged from detecting a bend in the Milky Way Galaxy to checking Einstein’s theory of gravity, General Relativity. But wanting to pursue here the relevance of Hipparcos to climate physics, I’m pleased to see that Michael Perryman points the way.

Michael Perryman. Photo by Richard Perryman

In The Making of History’s Greatest Star Map, pp. 236-243, Perryman notes the role of Hipparcos in refining observations the wobbles of the Earth’s axis, which are involved in the pacing of ice ages (the Milankovitch theory). Then he points to the link between solar activity and climate change, as evidenced by the Little Ice Age, the Medieval Warm Period and other variations. As to the mechanism for the solar connection, Perryman singles out the suggestion that cosmic rays, modulated by solar activity, influence cloud cover.

He continues the story with the Sun’s journey through the Galaxy and the icy intervals on Earth that correspond to exposure to intense cosmic rays when passing through spiral arms. That’s a major topic in The Chilling Stars and, as Perryman says, the Hipparcos data have improved our knowledge of motions in the Galaxy.

It’s reassuring when a professor of astronomy with no scientific or political axe to grind gives serious attention to the cosmic-ray/climate link (the Svensmark hypothesis). Let me reciprocate by reviewing what’s said about the climate-related significance of Hipparcos and its successor Gaia in The Chilling Stars and see if it needs updating or extending.

Read the rest of this entry »


2.75 million years ago

16/05/2010

Climate Change – News and Comments and Updating The Chilling Stars

Why the big freeze 2.75 million years ago?

The CO2 folk are flummoxed. In the current issue of Science (14 May) William F. Ruddiman of the University of Virginia wrings his hands over the mismatch between unchanging carbon dioxide levels and the drastically cooling climate over the past 20 million years. “Major glaciations began in the Northern Hemisphere around 2.75 million years ago, after a long prior interval of climatic cooling,” Ruddiman says, “… but our understanding of the driving forces behind the cooling remains incomplete.”

For Henrik Svensmark and me, an explanation for that big freeze of 2.75 million years ago is the “jewel in the crown” of climate history, because of its importance for the subsequent origin of the first human beings.Here’s a picture from The Chilling Stars of one of the earliest known stone tools, which were made less than 200,000 years after the big freeze began.

But if you want CO2 to be the big driver of climate change, as Ruddiman evidently does, the commonly used data are disobedient. Here are his graphs.

(A) Oxygen-18 index of deep-ocean temperature and ice volume (after Miller & Fairbanks1987 and Zachos et al. 2001). (B) Estimates of past CO2 concentrations from alkenones (after Pagani et al. 2005). Source: W.F. Ruddiman, Science, 14 May 2010, p.839.

Ruddiman thinks that the data must be wrong. He suggests pushing the CO2 up a little, 20 to 10 million years ago (using boron/calcium ratios) and finding a decline between 5 and 2 million years ago in new alkenone data. He concludes, “Geochemists still have work to do in refining the CO2 proxies.”

But that would be wasted effort if CO2 were not the driver. In The Chilling Stars Henrik Svensmark and I tell a completely different story about what was happening 2.75 million years ago. In Postscript 2008 we relate how the Sun and Earth, wandering through the Galaxy, blundered into a region of space packed with extra cosmic rays – just what was required to chill the world by making more low clouds, in accordance with the Svensmark hypothesis.

Read the rest of this entry »


Puzzling Sun

12/05/2010

Climate Change – Updating The Chilling Stars

The deeply puzzling Sun

We can’t predict the climate on Earth until we understand these changes on the Sun.” So says Jeff Kuhn, who runs the Haleakala Observatories of Hawaii’s Institute for Astronomy, and his sentiment will be shared by anyone who thinks that the Sun plays a major part in climate change.

Impression of the long-lived SOHO. ESA & NASA

He makes the comment in a press release (11 May 2010) about a remarkably small change in the Sun’s diameter in the course of the most recent sunspot cycle, Cycle 23. With colleagues from Universidade Estadual de Ponta Grossa (Brazil) and Stanford University, Kuhn reports in an International Astronomical Union paper:

“… the method and results of precise solar astrometry made with the Michelson Doppler Imager (MDI), on board the Solar and Heliospheric Observatory (SOHO), during one complete solar cycle. We measured an upper limit to the solar radius variation, the absolute solar radius value and the solar shape. Our results are 22 [milli-arcseconds] peak-to-peak upper limit for the solar radius variation over the solar cycle, the absolute radius was measured as 959.28 ± 0.15 [arcseconds] at 1 [astronomical unit], and the difference between polar and equatorial solar radii in 1997 was 5 km and about three times larger in 2001.”

In plain language, the visible Sun’s diameter changed by less than one millionth during 12 years of observation. That’s despite the daily frenzy of solar activity and the great contrasts in behaviour during the maxima and minima of the sunspot counts. Kuhn hopes for even more precise measurements with NASA’s newly launched Solar Dynamics Observatory, but to see long-term changes you must obviously watch for a long time. It’s the durability of the ESA/NASA SOHO spacecraft and its MDI instrument, since the launch in December 1995, that makes the present results possible.

MDI is widely known for its daily images showing us where the sunspots are. At the time of this posting on12 May the Sun’s face is spotless, and the extraordinary wait continues for our lazy star to get going in earnest with its new Cycle 24.

MDI also peers into the solar interior by “helioseismology” and can even detect the presence of sunspots on the Sun’s far side. What’s more, MDI measures the line-of-sight magnetic field at the visible surface, thanks to which David Hathaway of NASA Huntsville and Lisa Rightmire of the University of Memphis can describe another change during Cycle 23.

Read the rest of this entry »


Monsoons and the Sun

01/05/2010

Climate Change: Updating The Chilling Stars

Monsoons and the Sun

Late rains saved most of the 2009 harvest of India, despite a shortfall of 21% in the summer’s rainfall that led to a ban on rice exports, after a 17% loss of production in West Bengal. But 2009 saw the worst deficit in India’s summer monsoon since 1972, while Burma (Myanmar) had its the shortest monsoon season since 1979.

It is chastening to recall that, in April 2009, Reuters reported the Indian Meteorological Department as saying, “IMD’s long range forecast for the 2009 south-west monsoon season (June to September) is that the rainfall for the country as a whole is likely to be near normal.” Even an updated forecast in June expected only a small rainfall deficit. Clearly, the unpredictable monsoons remain a problem for meteorology and climate physics.

Is there a link between reduced monsoon rains and the Sun’s recent sluggish behaviour, shown by the scarcity of sunspots? Probably. But to clarify the solar link well enough to make better regional forecasts, for even a few months ahead, remains an urgent task. Read the rest of this entry »


Follow

Get every new post delivered to your Inbox.

Join 151 other followers