Last of the Dinosaurs and the Crater of Doom

The Cretaceous-Tertiary Extinctions

Big kill-off 65 million years ago.
60 % of plant and animal species went extinct.
All large land animals.
What happened?

The Crater of Doom

Tell-tale hint was world-wide layer of clay laid down about this time. There was an enhanced abundance of the element Iridium.
Iridium is of enhanced abundance (relative to Earth) in meteorites.
Physicist Luis Alvarez of the University of California suggested that the aftermath of a giant impact had caused these extinctions.

Chicxulub Crater

Probable “killer crater” identified only in last few years.
Chicxulub on coast of Yucutan. Covered at present time. >>>>>>> picture from Web page.
Crater is about 200 kilometers in diameter, therefore produced by impactor about 20 kilometers in diameter. Artist’s conception in Figure 7.18 of text.
Impact dated to 65 Myr ago.
Huge effect; glass beads from rock melt found all over the Caribbean basin.
Probable mechanism of extinction: world-wide blanket of cloud caused by smoke and ash that took years to settle out. See Figure 7.20 for computer simulation of event in progress.

Other Big Extinctions

Recommended book, “The Sixth Extinction” by Richard Leakey.
There have been 5 major extinction episodes since complex life arose on Earth about 580 million years ago. The Cretaceous-Tertiary (K-T) was the last of them. >>>>> Diagram from Leakey’s book.
Most extreme was the “End Permian”, or Permian-Triassic, 250 million years ago.
Quote from Science magazine, September 8 issue: “There was no hiding from the greatest mass extinction of all time. Two hundred and fifty million years ago, at the end of the Permian period and the beginning of the Triassic, 85 % of the species in the sea and 70 % of the vertebrate genera living on the land vanished”.
>>>>>>> Figure from Science magazine showing abruptness of extinctions.
Did an impact cause this too? “For the moment, an impact is just one of several contenders to explain the P-T extinctions”.
It is certainly possible that a big impact, or some other astronomical agent, was responsible for this event. But for now it remains a speculation.
Recommended reading to you: p162, section “Impacts and the Evolution of Life”. This is a suggestion that big impacts, and not natural selection, are the main steering wheel of evolution.

“Laying on of Hands”, a tactile experience.

The Origin of the Moon

VENUS

Now let’s talk about another planet. I will have a bit of departure from the syllabus, since Venus is so prominent in the evening sky. It is (quite appropriately) lumped together with Mars in your textbook under the chapter heading of “Earth-like planets”.

“Just the Facts, Maam”

Look at Table 9.1 of the textbook. Nice comparison of Earth, Venus, and Mars. Physical characteristics of Venus and Earth are astonishingly similar.

Semimajor axis: 0.72 au
Orbital period: 0.61 years
Mass: 82 % that of Earth
Diameter: 12,102 kilometers (versus 12756 for Earth!)
>>>>>> Second unveiling of the “Famous Picture”

The Basic Reality of Venus

The planet is eternally covered by a cloud layer. You cannot see the surface (at visible wavelengths) from outer space.

Nasty Surprises about Venus

Discoveries date from late 1950’s (about time of the movie “The Queen of Outer Space”, with Zsa Zsa Gabor).
Atmospheric pressure at surface = 90 atmospheres!
Surface temperature = 730 Kelvins (850 degrees Fahrenheit).
Quote from textbook: “One of the major challenges presented by Venus is to understand why the atmosphere and surface environment of this twin have diverged so sharply from those of our own planet”.
Most fundamental reason given in Table 9.2 of book. Atmosphere of Venus is nearly all carbon dioxide (CO₂ ) 96 percent rather than 0.03 percent here on Earth. Nitrogen is about 3.5 % on Venus.
Venus has a powerful Greenhouse Effect. It is not reassuring that we are increasing the carbon dioxide content of the Earth’s atmosphere.
Interesting description of runaway Greenhouse effect on p198. It is, however, quite speculative.