Tag Archives: Proterozoic

Snow time

744-704 million years ago

Tweeting was sparse for the past week, because for a billion years Earth was fairly stable. Any biological evolution towards greater complexity that was going on left little fossil evidence.

Then things changed dramatically. Before 720 million years ago, we find thick limestone deposits left by decaying algae. These were sequestering carbon, taking carbon dioxide out of the atmosphere, and cooling the Earth. At some point a positive feedback cycle kicked in, as polar seas froze and reflected more sunlight, cooling the planet further. The result was a succession of extreme Ice Ages. The Ice Age of the last few million years, which merely covered high latitudes with glaciers, off and on, were nothing compared to the Snowball Earth of the Cryogenian: at a minimum, polar seas were frozen, and tropical seas were slushy with icebergs. It’s possible that things were even more extreme: the entire sea may have been covered by a thick layer of ice, with a few photosynthetic algae surviving in the ice, and other organisms hanging on around deep sea hot water vents. For a hundred million years, climate oscillated abruptly between two steady states, frozen and warm.

It’s only in the last two decades we’ve begun to figure out this amazing story. If there’s a lesson here, it’s that Earth over the long run is far from a stable system. We will see again and again that the history of life, like human history, has been punctuated by catastrophes.

Advertisements

Slow weather and the world inside

Inside planet Earth is another planet, the size of Mars. Not quite the way Jules Verne or Edgar Rice Burroughs imagined, but …

We live at the boundary between Earth’s solid surface, its liquid water surface, and its atmosphere. The sun pours energy into this boundary, and drives the circulation of water and air. The altitude of the surface varies. Events on this boundary rule our lives. We live at the mercy of weather, worry about climate change and rising sea levels, and (if we are Tibetans or Andean Indians) have genes adapting us to life at high altitude.

There is an equally dramatic landscape 1800 miles deep in the Earth, at the boundary between the oxygen-rich silicate mantle and the iron core. The core-mantle boundary is as dramatic a transition as the Earth-atmosphere boundary. And the boundary is not smooth or featureless: We know, from measuring the choppy irregular pattern of seismic waves that bounce off it, that there is a complex uneven landscape at the boundary. There is a kind of slow weather in the mantle, driven not by the sun, but by heat from the core. The core-mantle boundary has cool uplands where material falling faintly through the viscous mantle from above lays thickly drifted, in mountains hundreds of miles high. It has torrid lowlands, from which hotter, less viscous plumes of magma rise, to generate hotspots far above. (Two of the major plumes nowadays are under the central Pacific and Africa.) And there may also be lakes and seas of liquid silicates at the boundary.

Long-term geological processes – the movement of tectonic plates, the formation and breakup of continents – are driven by this slow weather in the mantle. One theory is that things changed around the end of the Archaean and beginning of the Proterozoic — that the “weather” inside the Earth grew calmer, the lower and upper mantle grew more separate, and the modern pattern of supercontinent formation and breakup began. If this is true, then changes we see at the surface of the Earth, like the rise of an oxygen atmosphere, may owe something to events where mantle meets core.

Snow time

Tweeting was sparse for the past week, because for a billion years Earth was fairly stable. Any biological evolution towards greater complexity that was going on left little fossil evidence.

Then things changed dramatically. Before 720 million years ago, we find thick limestone deposits left by decaying algae. These were sequestering carbon, taking carbon dioxide out of the atmosphere, and cooling the Earth. At some point a positive feedback cycle kicked in, as polar seas froze and reflected more sunlight, cooling the planet further. The result was a succession of extreme Ice Ages. The Ice Ages of the last few million years, which merely covered high latitudes with glaciers, were nothing compared to the Snowball Earth of the Cryogenian: at a minimum, polar seas were frozen, and tropical seas were slushy with icebergs. It’s possible that things were even more extreme: the entire sea may have been covered by a thick layer of ice, with a few photosynthetic algae surviving in the ice, and other organisms hanging on around deep sea hot water vents. For a hundred million years, climate oscillated abruptly between two steady states, frozen and warm.

It’s only in the last two decades we’ve begun to figure out this amazing story. If there’s a lesson here, it’s that Earth over the long run is far from a stable system. We will see again and again that the history of life, like human history, has been punctuated by catastrophes.

Slow weather and the world inside

Inside planet Earth is another planet. Not quite the way Jules Verne or Edgar Rice Burroughs imagined, but …

We live at the boundary between Earth’s solid surface, its liquid water surface, and its atmosphere. The sun pours energy into this boundary, and drives the circulation of water and air. The altitude of the surface varies. Events on this boundary rule our lives. We live at the mercy of weather, worry about climate change and rising sea levels, and (if we are Tibetans or Andean Indians) have genes adapting us to life at high altitude.

There is an equally dramatic landscape 1800 miles deep in the Earth, at the boundary between the silicate mantle and the iron core. The core-mantle boundary is as dramatic a transition as the Earth-atmosphere boundary. And the boundary is not smooth or featureless: We know from measuring the speeds of seismic waves that there is a complex uneven landscape at the boundary. There is a kind of slow weather in the mantle, driven not by the sun, but by heat from the core. The core-mantle boundary has cool uplands where material falling slowly through the viscous mantle from above has piled up. It has hot lowlands, from which hotter, less viscous plumes of magma rise, to generate hotspots far above. (Two of the major plumes nowadays are under the central Pacific and Africa.) And there may also be lakes and seas of liquid minerals at the boundary.

Long-term geological processes – the movement of tectonic plates, the formation and breakup of continents – are driven by this slow weather in the mantle. One theory is that things changed around the end of the Archaean and beginning of the Proterozoic — that the “weather” inside the Earth grew calmer, the lower and upper mantle grew more separate, and the modern pattern of supercontinent formation and breakup began. If this is true, then changes we see at the surface of the Earth, like the rise of an oxygen atmosphere, may owe something to events where mantle meets core.

Snow time

Tweeting was sparse for the past week, because for a billion years Earth was fairly stable. Any biological evolution towards greater complexity that was going on left little fossil evidence.

Then things changed dramatically. Before 720 million years ago, we find thick limestone deposits left by decaying algae. These were sequestering carbon, taking carbon dioxide out of the atmosphere, and cooling the Earth. At some point a positive feedback cycle kicked in, as polar seas froze and reflected more sunlight, cooling the planet further. The result was a succession of extreme Ice Ages. The Ice Ages of the last few million years, which merely covered high latitudes with glaciers, were nothing compared to the Snowball Earth of the Cryogenian: at a minimum, polar seas were frozen, and tropical seas were slushy with icebergs. It’s possible that things were even more extreme: the entire sea may have been covered by a thick layer of ice, with a few photosynthetic algae surviving in the ice, and other organisms hanging on around deep sea hot water vents. For a hundred million years, climate oscillated abruptly between two steady states, frozen and warm.

It’s only in the last two decades we’ve begun to figure out this amazing story. If there’s a lesson here, it’s that Earth over the long run is far from a stable system. We will see again and again that the history of life, like human history, has been punctuated by catastrophes.

Nuclear life and sulfurous seas

A week of tweets, beyond bacteria and the “Canfield Ocean” (in the sea, little oxygen and life living on sulfates)

Sunday, February 8. 1.634 – 1.544 Bya

Saturday, February 7. 1.728 – 1.634 Bya

Friday, February 6. 1.828- 1.728 Bya

Thursday, February 5. 1.933 – 1.828Bya

Wednesday, February 4. 2.045 – 1.933 Bya

Tuesday, February 3. 2.163 – 2.045 Bya

Monday, February 2. 2.288 – 2.163 Bya

Slow weather and the world inside

Inside planet Earth is another planet. Not quite the way Jules Verne or Edgar Rice Burroughs imagined, but …

We live at the boundary between Earth’s solid surface, its liquid water surface, and its atmosphere. The sun pours energy into this boundary, and drives the circulation of water and air. The altitude of the surface varies. This rules our lives. We live at the mercy of weather, worry about climate change and rising sea levels, and (if we are Tibetans or Andean Indians) have genes adapting us to life at high altitude.

There is an equally dramatic landscape 1800 miles deep in the Earth, at the boundary between the silicate mantle and the iron core. The core mantle boundary is as big a transition as the Earth atmosphere boundary. It is not smooth or featureless: We know from measuring the speeds of seismic waves that there is a complex uneven landscape at the boundary. There is a kind of slow weather in the mantle, driven by heat from the core. The core mantle boundary has cool uplands where material falling slowly through the viscous mantle from above has accumulated. It has hot lowlands, from which hotter, less viscous plumes of magma rise, to generate hotspots above. (Two of the major plumes nowadays are under the central Pacific and Africa.) And there may be lakes and seas of liquid minerals at the boundary.

Long-term geological processes – the movement of tectonic plates, the formation and breakup of continents – are driven by this slow weather in the mantle. One theory is that things changed around the end of the Archaean and beginning of the Proterozoic — that the “weather” inside the Earth grew calmer, the lower and upper mantle grew more separate, and the modern pattern of supercontintent formation and breakup began. If this is true, then changes we see at the surface of the Earth, like the rise of an oxygen atmosphere, may owe something to changes where mantle meets core.