Saturday, May 30, 2015

Oxygen and Mcrobes and Algae and the Early Earth

Q: Hi!
Oxygen in our atmosphere was created by small creatures who had just invented a new process:  photosynthesis.
The waste product of photosynthesis is oxygen.
After an unfathomable number of  years, too much O2 built up in the atmosphere, changing the greenhouse gas, methane, into carbon dioxide, which isn’t such a strong greenhouse gas.  This caused the earth to cool off to the point where the first known ice age began, the huronic, I think.  It lasted for millions of years and enveloped the entire earth with ice.
Question 1: how did these photosynthetic creatures survive in an iced-over earth?
Question 2: what caused the end of this very long ice age?
 Just curious - Thank you!
 - Susan K

A: Your question suggests you are well along in studying this topic. I've stored a number of closely related questions and answers on this blog, and by way of a long answer, some of these may help:

The medium-length answer: Our atmosphere passed through the oxygenation transition around 2.5 billion years ago, and it certainly involved photosynthesis - stromatolites (fossil algal clumps) have been found dating as far back as 3.3 billion years. However, there are also suggestions that mantle outgassing, tectonics, and oceanic current-shifts may have contributed. There really was a Snowball Earth episode, and there have been a series of cold-warm cycles since then. Scientists have been exploring - with limited data - what could have caused these events, and suggestions range from the fairly mundane to the exotic: asteroid impact, tectonic change that interrupted oceanic current flows, etc. The Chicxulub asteroid event 65 million years ago certainly knocked the oxygen levels in the atmosphere down dramatically, requiring millions of years to recover. This is almost certainly why bar-headed geese can easily fly over Mount Everest: birds have evolved a truly advanced respiratory system since that event. Evolution is well-documented to speed up under environmental stress.

Some short answers:
1. If there is one thing certain about microbial life, it is that it can survive almost anything. Microbes have been found kilometers deep in the Earth, and temperatures steadily increase with depth due to radio-isotope decay in the Mantle and Core of the Earth (the temperature rises to typically 60 C at 4,000 meters depth).

2. There are a lot of variables that may have been involved in the recurring cool-warming cycles, including the fact that the Sun has steadily grown in luminosity during its lifetime, as well as tectonics, and methane-emitting life forms. Likely a combination of these - and probably other factors - led to out-of-control feedback loops that dead-ended in climate extremes before the atmosphere eventually  recovered. 

Saturday, May 23, 2015

Damage Earthquakes Cause

Q: What kind of damage can a(n) earthquake do?
- Carrera K

A: Earthquake damage can be very wide-ranging. In increasing order of destructiveness (roughly following magnitudes from M ~4 to M ~ 8) :

1. Small cracks form in drywall, stucco, and concrete walls of buildings.

2. Fragments of building fall into the surrounding streets - glass, or bricks from the corners of windows, etc.

3. Topographic settling, leading to serious internal structural damage in buildings, making them uninhabitable (San Francisco, Loma Prieta earthquake, 1979).

4. Large fractures form in soils and rocks. Water towers fail. Electric power is cut and gas lines rupture (White Wolf Fault, Bakersfield, CA, 1952).

5. Major fires start that are difficult or impossible to control (San Francisco, 1906 AD).

6. Collapse of concrete floors in buildings, crushing most of what lies within (Izmir, Turkey, 1999 and 2013).

7. Major infrastructure collapse, leading to water-borne diseases, and starvation happens on a wide scale (Haiti, 2010).

8. Tsunamis wreak broad damage to coastlines, killing most people within reach of the water (Aceh, Indonesia, 2004).

9. Allocthons and major landslides cover or sweep inhabited regions. Segments of coastline drop below sea level (Puget Sound, 1700 AD), and rivers temporarily reverse direction (Mississippi River, 1811).

10. Entire civilizations collapse and do not recover (the Minoan civilization, 1,500 BC, though how much was explosive volcanism and how much was caused by earthquake damage is unclear).