age of earth and solar system ….4.5-4.6 bya (radioisotopic dating of meteorites)

Age of earth and solar system….4.5-4.6 bya (radioisotopic dating of meteorites)

Early impacts were colossal

A Mars sized chunk hit earth and dislodged a chunk of earth that became the moon

Some solid crust by about 4 bya

(some rocks in Canada are 3.96 billion years old).

Surface water by about 3.8 bya

(sedimentary rocks of that age in Greenland)

How do we define life?

What steps do you need to get evolution of life?

What steps do you need to get evolution of life? P459

1.Small organic molecules (like amino acids)

2.Joining of these into longer macromolecules (like proteins, nucleic acids)

3.A packaging of some sort

4.Origin of self replication

1. Small Organic Molecules like amino acids?

Miller and UreyHydrogen methane and ammonia

2. Assembly of these building blocks into polymers

Now we need to get them together into proteins and nucleic acids

Drip solutions onto hot rocks evaporation borders encourage polymerization (hooking together)

or Ice!

Miller and Bada

As an ice crystal forms, it stays pure: Only molecules of water join the growing crystal, while impurities like salt or cyanide are excluded.

These impurities become crowded in microscopic pockets of liquid within the ice, and this crowding causes the molecules to collide more often.

Chemically speaking, it transforms a tepid seventh-grade school dance into a raging molecular mosh pit.http://discovermagazine.com/2008/feb/

3. Packaging-Acquire cellular form

We know now that membranes often form spontaneously under certain circumstances-vesicles

Hydrophobic molecules in a mixture organize into a bilayer at the surface of droplets like the lipid bilayer of a plasma membranes

This will control entry and exit from the “cell”

4. Origin of self replicating polymers

RNA world

Important in protein synthesis but also can take on enzyme like functions.

DNA probably evolved later as a safe depository for genetic info-more stable

So what evidence do we see for early life?

Oldest fossils of ProkaryotesStromatolites p440

Similar to Cyanobacteria (3.5bya)

Relatives still exist in Western Australia

Chemical fingerprints-Carbon Isotope

(Harrison, Manning and Mojzis)

Remember those sedimentary rocks in Greenland (3.85)..

Those rocks have been heated and squished so unlikely to see fossils but…

Look at carbon isotope ratios and can detect presence of life..

“The carbon aggregates in the rocks have a ratio of about 100-to-one of 12C (the most common isotope form of carbon, containing six protons and six neutrons) to 13C (a rarer isotopic form of carbon, containing six protons and seven neutrons). The light carbon, 12C, is more than 3 percent more abundant than scientists would expect to find if life were not present, and 3 percent is very significant……..”

http://www.sciencedaily.com/releases/2006/07/060721090947.htm

Where??Surface ponds-Primordial soup-Surface dangerous!

Why?

Deep sea vents- Interesting amino acids form there

“The worst impacts would have been 10-100 million years apart and a handful of hardy bacterial souls could have survived at the bottom of the oceans….”

Science News December 2000

Other planets?

Panspermia hypothesis…

Europa (moon of JUPITER) water and active volcanoes -hydrothermal vents in liquid ocean capped by ice??

Mars-today is cold and dry but had liquid water and it may have had an atmosphere that warmed it…

What else do we know?

We do find large spherical organic molecules called fullerenes at meteor impact sites.

Bacteria can survive outer space!

Last fall…. (Time Magazine description of article in PLOS)

That adds up to about 20 billion Earths in our galaxy alone, says lead author Erik Petigura, of the University of California, Berkeley. That in turn means that an Earth-like world is likely to be just 12 light-years away, and that its parent star is visible to the naked eye. “It’s really amazing when you think about it,” Petigura says.

Read more: 20 Billion Earths in the Milky Way Alone? | TIME.com http://science.time.com/2013/11/04/so-much-for-earth-being-special-there-could-be-20-billion-just-like-it/#ixzz2mKVgqMRv

Figure 23.10

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Precambrian before about 500mya

Prokaryotes

Eukaryotes-1.8bya is fossil date for evolution of multicellularity but is some evidence for much earlier

Cambrian explosionPaleozoic

End Permian ExtinctionMesozoic

Cretaceous Extinction Cenozoic

Cambrian explosion about 500mya (550mya)

Nearly all major “styles” or body plans of animals appear!

Major evidence is from Burgess Shale in B.C. CANADA (also from China and Greenland)

Are earlier fossils of animals but are soft and squishy (see Fig 25.2 p483 bottom right Ediacaran)

Paleozoic Period about 500-250myaClimate-Moist SwampyPlants-ferns, mosses, horsetailGiant insects

Many diverse amphibians were large! 9ft

Science DailyTiktaalik roseae, an early tetrapodomorph (late Devonian period, ~380 M. y. ago) (Credit: Arthur Weasley, GNU Free Documentation licence)

And scary fish

nationalgeographic.com

Many Diverse Synapsids (p 441 mentioned)

A dicynodont

Thrinaxodon-cynodont

More Synapsids

Figure 23.4a

OTHERTETRAPODS

Reptiles(includingdinosaurs and birds)

Mammals

†Very late (non-mammalian)cynodonts

†Dimetrodon

Cyn

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Figure 23.10

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End Permian-250myaEffect 90-96% of all species

Who Extinct? Synapsids, many Amphibians!Giant insects-dragonflies, cockroachesHorsetail trees, Tree ferns (some)

Why?Huge amounts of lava oozing out of the earth SiberiaFormation of PangaeaMixing of oceans slows-anoxic

http://www.nationalgeographic.com/ngm/0009/feature4/

Mesozoic about 250-65mya•Since Pangaea had formed===DRY•Plants-conifers…•Dinos super diverse! Mammals around..•Flying and pollinating insects begin to diversify with flowering plants

PterosaursPlesiosaursIchthyosaurs Dinosaurs

Figure 23.10

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Cretaceous Extinction event (K/T)!

7 miles across…

Cretaceous (K/T)

Effect 50% of all species

Who? Dinosaurs, Pterosaurs, Plesiosaurs, many small marine species

On land nothing bigger than 25 kgs survived-all survivors were small

Why? Impact

There is debate about the precise role of the impact on Dinosaur Extinctions..

Opinions range from….

•Impact was the cause

•Impact was one of the causes

•Impact was the straw that broke the camel’s back (dinos were in decline before the impact)

Cenozoic -65mya to present

Spreading apart of continents..

Flowering plant diversity accelerates

Insects continue dramatic diversification

Mammals diversify

More Mass Extinction…

Catastrophism

So.. Although classic “Darwinian” slow adaptive evolution is important….

we now appreciate the role of catastrophic events (chance events) in the evolution of the diverse forms of life on the planet!

Remember…there is a creative side.. Extinctions open up new space for “adaptive radiations”

•Ex. Mammals after Cretaceous extinction event

•Ex. Dinos diversified after End-permian extinction when Synapsids extinct

The species alive today are only a tiny fraction of all those that have ever lived.

•The vast majority of all species in the history of the planet have gone extinct.

•So extinction is normal

•Average lifespan of a species from its origin to its extinction is between 1 and 5 million years

Species Average Lifespan years (MYA)

All Invertebrates Raup (1978) 11Marine Invertebrates Valentine (1970) 5–10Marine Animals Raup (1991) 4Marine Animals Sepkoski (1992) 5All Fossil Groups Simpson (1952) .5–5Mammals Martin (1993) 1Cenozoic Mammals Raup and Stanley (1978) 1–2Diatoms Van Valen 8Dinoflagellates Van Valen (1973) 13Planktonic Foraminifera Van Valen (1973) 7Cenozoic Bivalves Raup and Stanley (1978) 10Echinoderms Durham (1970) 6Silurian Graptolites Rickards (1977) 2

Adapted from the book “extinction rates”, edited by Lawton, J, and May, R.[8] Wikipedia!!

Figure 23.10

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How long did it take for diversity to recover after Permian extinction event? ESTIMATE!!!

www.geol.umd.edu/.../lectures/natresources.html