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How Earth began orbiting the Sun

Also: where cells get energy.  Why an EKG is 'EKG' instead of 'ECG'

Q: How did Earth start rotating around the Sun, and how did the Moon begin rotating around the Earth? Will Earth ever escape the Sun's orbit? Was Earth in a different orbit long ago? Will it change in the future? Since the Sun is changing in size slightly, will Earth's orbit about the Sun change? Will Earth ever be pulled into the sun (given enough time)?  Terry, Albuquerque, NM

This view of the rising Earth greeted the Apollo 8 astronauts as they came from behind the Moon during one of their orbits about the Moon. Dec. 24, 1968. Photo courtesy of NASA.

A: Earth started rotating about the Sun — and the Moon about Earth — because the elements that evolved into the Sun, Earth, and Moon were already spinning. Most astronomers believe the same process that forms stars, also creates planets and their moons.

Our solar system started as an interstellar cloud of gas and dust. The cloud (our beginning) was roughly spherical; it revolved around the center of the galaxy, and spun about its own center. All things in the Universe spin in some way, and the nebula cloud was no exception.

Under the force of gravity the nebula collapsed into a spinning disk, which eventually became the Sun and planets. Earth spins about the Sun because the primordial disk that evolved into the planets spun about a central mass, which gradually evolved into the Sun.

The Moon rotates about Earth as a result of its creation. A Mars-sized body slammed into Earth and ejected a plume of matter into orbit around Earth. The plume became a ring of rubble circling Earth, which coalesced into the Moon, which continued orbiting Earth.

Even an impact by a Mars-sized body failed to dislodge Earth from its orbit around the Sun, although the impact probably did change our axis of spin to the present 23.5 degrees to the plane of the solar system. To escape the Sun, Earth would require a speed of 11,000 mph (5  km/s) over its orbital speed of 67,000 mph (30 km/s). It's difficult to envision a force that could accelerate the mass of Earth to such a speed and therefore improbable Earth will ever escape the Sun.

Earth may have been in a slightly different orbit before the Mars-sized body hit it but is unlikely to change much in the future. Earth's orbit has been relatively stable for over four billion years with little sign of change in its predictable orbits for at least the next five billion years. Although the Sun is shrinking slightly, astronomers believe this is a temporary contraction and has negligible effect on Earth's orbit.

No, Earth will not fall into the Sun — not a chance because in five billion years the Sun will expand into a red giant. Instead of Earth falling into the Sun, the Sun will balloon out and perhaps engulf Earth, evaporating our world into a puff of silicate and iron smoke.

Further Surfing:

Space.com: Earth might have been a ringed planet, like Saturn

Q: What are mitochondria? Is that where we get our energy?

McChord AFB, Washington. 1st Lt. Richard Cullen plays goal keeper with the Seattle Sounders. Mitochondria supplies the energy.  Photo courtesy of Master Sgt. Lance Cheung, the US Air Force and Wikipedia.

Q: Are mitochondria present in all plants and animals? What is the current theory on how mitochondria evolved? Are they all the same? Someone, Texas, USA

A: "Biology Department, UNM" a young woman answers the phone.

I ask to speak with an expert on mitochondria (my-toe-KON-dree-a). She pauses.

"What's mitochondria?" I hear her say to a friend.

Mitochondria are tiny sacs—so small you need an electron microscope to see them—elongated, like a sausage. Many bop around in each heart, pancreas, or kidney cell. Few live in a skin cell. All living cells, however, have mitochondria (except bacteria and cyanobacteria, formerly called blue-green algae).

Mitochondria power life. Their job is to burn food and produce power packets (called ATP molecules, whose initials stand for Adenosine Tri Phosphate).

The young woman comes back on the phone and refers me to Don Natvig, a molecular biologist and professor at the University of New Mexico. Unfortunately, he's in a tearing hurry, gives me quick answers, and promises more when I call back at 3.

Back I go to surfing the web. How did mitochondria evolve? A mouse click gives the answer.

Earth formed 4.5 billion years ago. Life began a billion years later as one-celled bacteria so primitive they had no nucleus. Bigger cells with nuclei evolved about 2 billion years after that.

Around then, or in another 700 million years, mitochondria developed. Current theory says a big cell engulfed a little one or a little one infected a big one.

The big cell refrained from digesting or destroying the little fellow. Both profited. The big guy gained extra power packets and the little guy found food and a stable home. The mutual symbiotic relationship persisted and now is so strong that each cannot survive without the other.

It is 3 o'clock and time to call Don, the molecular biologist. I ask my question: do mitochondria differ between plants and animals?

"Yeees," he draws out the answer. "But their function is the same in both. They make ATP (power packets). The difference is like that between a Chevy and a Ford." Not much.

He produces examples. "Plant and animal mitochondria have slightly different genes and differ a bit in how they process them."

Mitochondria have their own genes, separate from the genes inside each cell's nucleus. What's more, mitochondrial genes come only from the mother, not both parents. In fact, the FBI tracks maternal relatives using mitochondrial DNA.

Further Surfing:

On line biology, M. J. Farabee: How a cell is organized

Q: If "EKG" stands for electrocardiogram, why isn't it spelled "ECG"? Sandra, Albuquerque, NM

An EKG image.  Photo courtesy of Charles S. Kirby, MA, Columbia-Presbyterian Hospital.

The term comes from the German spelling of electrocardiogram: Eletrokardiogramm.

The EKG inventor, however, was Dutch —Willem Einthoven. In 1893, Einthoven introduced the Dutch word, electrocardiogramm, at a meeting of the Dutch Medical Association. Thus, Einthoven originally spelled the word with a "C".

It was not until 1900 that Einthoven changed the spelling to 'Eletrokardiogramm' when he published in German. The first abbreviation was EKG. Now both terms are in common usage: ECG and EKG.

(Answered Sep. 27, 2002; updated on Aug. 28, 2007)

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