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.

Mars

Today begin several lectures on Mars. Mars is a terrestrial planet we know a lot about, and it has always been associated with the question of life elsewhere in the universe. Today that connection is closer and more compelling than ever. I would bet that in the next twenty years we will know fairly definitively whether life has ever existed on Mars, or if it even exists at the present time.

Orientation

First let’s start with some basic orientation information.

View of the solar system
Right now, Mars is 0.87 astronomical units from us.
The celestial coordinates of Mars are RA=18h55m, Dec=-25degrees43min. Plot it up on your SC1 chart.

Just the facts, Maam

Diameter: 6378 kilometers versus 12756 for Earth (53%). >>>> famous transparency. Mars is a significantly smaller “ball in space” than Earth.
Mass 6.44 ‰ 10²³ kilograms (11 % that of Earth).
Density 3.9 grams/cc (Hey! What does this mean?)
Major axis of orbit 1.52 au.
Period of orbit 1.88 years.
Eccentricity of orbit 0.093 (rather high for a major planet).

Basic Observations and History of Study of Mars

With telescopes on Earth you can make out surface features on Mars. A good illustration is in Figure 9.2 of the book. Some of the features you can see are

Recurrent features such as Syrtis Major. With these you can tell the rotational period of Mars is almost exactly that of Earth, 24.6 hours.
Polar caps, seemingly like Earth.
Seasonal variations in the prominence of the surface features.
All of these observations were available between 100 and 150 years ago, and led to the idea that Mars was an Earthlike planet.

Percival Lowell and the Martians

At the end of the last century and the beginning of this one, Percival Lowell set up an observatory in Arizona and began careful observations of Mars. He thought he saw the famous Martian Canals (excellent illustration is Figure 9.3). These were believed to be the construction of intelligent Martians (see the 1960 movie Mars, the Angry Red Planet).

Mid Twentieth Century Physics and the Inhabitability of Mars

A number of discoveries were made with the improved knowledge of physics that we could bring to astronomical observations in the twentieth century. These made it clear that Mars could not really host intelligent life forms

The atmospheric pressure is about 8-9 millibars, far too low to support liquid water. The atmospheric pressure here on Earth is about 1013 millibars at sea level. At the cruise altitude of commercial aircraft it is about 300 to 350. To reach

8-9 you have to go 20 miles up.

The chemical composition of the atmosphere of Mars is quite different . Check Table 9.2 of the text. Note that the chemical composition of the atmosphere of Mars is almost identical to that of Venus. Notice also that the abundance of Argon is 1.6 % rather than 0.006%. It turns out that this (apparently stultifyingly) dull detail is actually an extremely important clue to the ancient history of Mars.
Because of the lack of an atmosphere, there are extreme variations in the surface temperature.