John, you said, “I've said this before and I'll say it again today. We've been sending out signals substantial enough to escape our solar system for 68 years”

Well, I've said this before and I'll say it again:

The most important and easily detected signals we send are those having to do with atmospheric gases and other signals from the effects of life and of intelligence.

I don’t think the footprint of life is small—it’s been broadcast for about four billion years with an antenna of about 600 million square kilometers. Even we, before the end of the next decade will be able to detect methane or oxygen producing life within 50 light years or so of Earth. By the end of the 21st century, it’s hard to imagine that capability won’t be extended to a distance of many thousands of light years.

I think, almost by definition, advanced ETs will be at least as capable as us, and here are some of the things we know ET can look for (ET, thousands of years more technologically advanced than us, certainly than me, will know a lot more):

1. Oxygen and Ozone at levels higher than possible from non-biological sources of which we are currently aware. More than 20 times higher over the last 600 million years, and more than 12 times higher for more than two billion years.

2. Methane in quantities not possible on a sustained basis from non-biological processes of which we are aware on a planet as hot, as irradiated and with as much oxygen as Earth. With varying strength this signal has been sent out from Earth for about four billion years.

3. One of the human introduced pollutants in our atmosphere is lead, which has been used in metal working for more than 8500 years. The Romans increased the lead identified in Greenland ice cores hundreds of times above normal levels 2500 years ago.

4. Coal has been widely used for more than a thousand years. Burning coal releases radioactive uranium and thorium into the atmosphere.

5. Chemicals which came into widespread use in the 19th century, such as DDT (1870s), kerosene, naphthalene and gasoline (1850s), benzene (1860s), and chloroform (1840s).

6. Widespread use of freon has taken place for the last 75 years. For those 75 years we’ve used a 600 million square kilometer antenna to broadcast 24/7-360 degrees that we use refrigeration, have substantial electrical distribution and freight delivery systems, fractional horsepower electric motors, measures of some kinds of industrial activity, and lots of other implications.

There are lots of other opportunities for advanced ET, such as remote detection of chlorophyll.

And there will be lots of opportunities for us, in the next thousand years, to exploit all of these possibilities and many more I don’t know about; that no human knows about—yet. We’re on the cusp of doing many of these things within most of our lifetimes.

What is ET to think of a world with the right temperature, water vapor, an oxygen atmosphere, and too mcuh methane? All things transmitted from Earth for at least 600 million years. And then add chlorophyll.

How could advanced ET not know we are here? At least, if they’re within a few thousand light years. By 3000 AD we would know.

Bob